This session focusses on hydrological response to changes in climatic forcing at multi-annual to multi-decadal timescales. Catchments are immensely complex and unique systems responding to external factors (e.g. changes in climate) on a variety of timescales due to complex interactions and feedbacks between their components. Recent evidence suggests a tendency for existing models and methods to downplay the impact of a given climatic change on streamflow with major implications for the reliability of such methods for future planning. The poor performance of models suggests they potentially misrepresent (or omit) important catchment processes, process timescales, or interactions between processes. The multitude of responses and feedbacks developing in the critical zone need to be disentangled and understood to improve our ability to make hydrological predictions under different and continuously changing climatic conditions.
We invite submissions on themes such as (but not limited to):
1. Better understanding of hydrological and/or biophysical processes related to long-timescale climate shifts potentially contributing to apparent shifts in hydrologic response;
2. Understanding and quantifying catchment multi-annual “memory”
3. Modelling studies aiming to evaluate and/or improve hydrologic simulations under historic climatic variability and change;
4. Efforts to improve the realism of runoff projections under future climate scenarios;
5. Studies that explore implications of long term-hydrologic change for water availability, risk, or environmental outcomes including interactions with human factors such as landuse changes, evolving water policy, and management intervention.
Mon, 23 May, 08:30–10:00
Chairpersons: Margarita Saft, Sina Khatami, Keirnan Fowler
It is common to test hydrologic models under contrasting historical periods as an indicator of likely performance under climate change. For example, a model calibrated under average conditions may be tested under increasingly dry subsets of the observational record. Any decline in performance as the testing conditions deviate further from the calibration conditions is then assumed to represent likely performance degradation under climate change scenarios with comparable rainfall decreases. Many studies have inherently applied the assumption that past rainfall variability can be used as a proxy for future climate change, but the analogy may be flawed for three main reasons:
- Due to lagged hydrologic response to meteorological shifts, catchment behaviour under long-term wetting or drying may not be fully represented over shorter wet or dry periods.
- Subsets of the past record selected based on rainfall are unlikely to reflect future temperature increases.
- Past observations do not include expected increases in carbon dioxide levels.
If any of these factors substantially impacts catchment response, subsets of the historical record with equivalent rainfall will not be accurate proxies for future climate scenarios. We tested the impact of each factor using the ecohydrologic model RHESSys. RHESSys dynamically simulates vegetation growth, subsurface flow and nutrient cycling and is thus able to capture the key processes that could drive nonstationary catchment response in the future. We found that all three future climate factors (rainfall change persistence, temperature, and carbon dioxide) altered catchment response substantially, especially for drier future scenarios. For our study catchment, persistence of dry conditions over many decades led to different subsurface water storage levels than the same rainfall experienced over shorter timeframes, leading to different streamflow. The impacts of increased temperature and carbon dioxide concentrations on vegetation further altered runoff behaviour. This means that long-term climate change effects will not necessarily emerge over short historical periods with equivalent rainfall. In our example, ignoring persistence in rainfall changes, rising temperatures, and higher carbon dioxide levels could lead us to underestimate model performance degradation in terms of Nash-Sutcliffe efficiency by as much as 0.41. Therefore, the uncertainty introduced in hydrologic models by future climate change has probably been underestimated in the current literature.
How to cite: Stephens, C., Marshall, L., Johnson, F., Lin, L., Band, L., and Ajami, H.: Can examining past variability help us understand catchment response to future climate change?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3319, https://doi.org/10.5194/egusphere-egu22-3319, 2022.
The widely-used Budyko framework synthesizes the competition between water and energy availability simply using climatological mean precipitation (P) and potential evaporation (PE). While PE within the Budyko framework is often regarded as the atmospheric evaporative demand (AED), AED can substantially differ from PE assuming ample water availability due to its responsive behavior to soil moisture. This could violate the independence assumption between P and PE underpinning the Budyko framework, potentially leading to ill-posed parameterization of land-surface properties. Here, we showed that the use of AED as PE in a Budyko equation could significantly disturb a global runoff sensitivity assessment to climatic and land-property changes. By linking a two-parameter Budyko equation and the complementary evaporation principle (CEP), we found that climatic changes play a more important role in altering runoff than a prior assessment would suggest. This study also suggests that linking the Budyko equation with CEP can isolate the responsiveness of AED to soil moisture, allowing more proper consideration of surface energy balance.
How to cite: Kim, D. and Chun, J. A.: Linking the Budyko framework with the complementary evaporation principle for proper consideration of surface energy availability, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10695, https://doi.org/10.5194/egusphere-egu22-10695, 2022.
Heavy rainfall in East Africa between late 2019 and mid 2020 caused devastating floods and landslides throughout the region. These rains drove the level of Lake Victoria to a record-breaking maximum in the second half of May 2020, when the lake reached its highest level since measurements began in 1948. The high lake levels and consequent shoreline flooding triggered international attention, with media sources proposing a causal link with climate change. However, a formal attribution study identifying the possible role of anthropogenic climate change in increasing the likelihood of such record-breaking water levels has not been carried out so far.
We present an attribution study that estimates how anthropogenic climate change influenced the likelihood of observing the rate of change in Lake Victoria’s level that was recorded in 2020. To this end, we reconstruct the record-high lake level using an observational water balance model for Lake Victoria. We first investigate the influence of the different water balance terms on the resulting lake level. Then, we apply the water balance model in a probabilistic event attribution framework by forcing it with historical and natural forcing only (hist-nat) bias-adjusted precipitation from six Earth system models from the Coupled Model Intercomparison Project phase 6 (CMIP6) ensemble, as made available through the Inter-Sectoral Impact Model Intercomparison Project phase 3b (ISIMIP3b). The study contributes to a better understanding of impacts caused by climate and weather extremes in the Greater Horn of Africa by disentangling the role of anthropogenic climate change and natural internal variability in a high-impact flood event.
How to cite: Pietroiusti, R., Vanderkelen, I., and Thiery, W.: Was the 2020 Lake Victoria flooding linked to anthropogenic climate change? An event attribution study, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2300, https://doi.org/10.5194/egusphere-egu22-2300, 2022.
Climate drives the hydrological response in a more complex way that would result from a water balance analysis. I this study such a complex, spatiotemporal behaviour of flooding a wetland catchment is presented over 200 years. The study site is the Biebrza River catchment located in north-eastern Poland. This medium size catchment, especially its floodplain, was preserved in a relatively unchanged state in the last centuries. The yearly floods in the wetland floodplain are driven by complex contribution water from precipitation, snowmelt, groundwater, and upstream river. The hydrological simulations were conducted using a fully-integrated groundwater-surface water hydrological model (HydroGeoSphere). The historical simulations were driven by the NOAA Twentieth Century Reanalysis, whereas the future climate simulation was driven by an ensemble of EURO-CORDEX downscaling datasets for rcp26, rcp45, and rcp85 pathways. The contribution of different water sources to the floods was analysed using the hydraulic mixing-cell method. The results show spatiotemporal trends and year-to-year variation of the flooding water composition, depth and extent in the analysed period. This complex response stresses the importance of taking into account full hydrologic system interactions, such as climate, timing and hydraulic feedbacks for climate change analysis.
How to cite: Berezowski, T.: Changes in groundwater, rainfall, snowmelt and river water contribution to floods in the 1900-2100 period for a wetland catchment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3810, https://doi.org/10.5194/egusphere-egu22-3810, 2022.
Around 60 percent of terrestrial precipitation on the global average transforms into evapotranspiration. However, reliable estimation of actual evapotranspiration (AET) is challenging as it depends on multiple climatic and biophysical factors. Despite developments such as remotely sensed AET products, AET responses to prolonged drought is still poorly understood. Therefore, this study focuses on understanding long-term changes and variability of AET prior to and during the Millennium Drought in Victoria, Australia. We also investigate the capability of commonly used rainfall-runoff models to simulate AET under multiyear droughts. Therefore, we employ simple sensitivity analysis to examine four different water balance approaches between pre-drought and drought periods in six different study catchments in Victoria. The first water balance approach is the simplest long-term water balance approach, partitioning long-term precipitation into evapotranspiration and runoff. The second water balance approach adopts a long-term change in storage to the water balance during the Millennium Drought by employing regional-scale change in GRACE estimates derived from Fowler et al. (2020). The third and fourth water balances are based on simulations from SIMHYD and SACRAMENTO. Surprisingly, the adoption of long-term change in storage during the Millennium Drought indicates that the annual rates of pre-drought AET were largely maintained throughout the drought; i.e. the rate was relatively constant with time. This suggests that AET gets priority over streamflow following a drying shift in precipitation partitioning; resulting in a relatively constant AET under multiyear drought. In contrast, the rainfall-runoff models underestimated AET during the drought compared to both water balance approaches. These results broadly acknowledge the need for model improvements to provide more realistic AET estimates under future drying climates and provide a new perspective on recent hydrological phenomena such as changing rainfall-runoff relationships in these regions. Furthermore, this sensitivity analysis was augmented and confirmed by a regional-scale water balance approach.
Keywords: Catchment water balance, Evapotranspiration, Change in storage, Rainfall-runoff models
References: Fowler, K., Knoben, W., Peel, M., Peterson, T., Ryu, D., Saft, M., Seo, K.W., Western, A., 2020. Many Commonly Used Rainfall-Runoff Models Lack Long, Slow Dynamics: Implications for Runoff Projections. Water Resour. Res. 56. https://doi.org/10.1029/2019WR025286
How to cite: Gardiya Weligamage, H., Fowler, K., Peterson, T., Saft, M., Ryu, D., and Peel, M.: Towards Understanding Evapotranspiration Shifts Under a Drying Climate, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13013, https://doi.org/10.5194/egusphere-egu22-13013, 2022.
Australia's Millennium Drought (1997-2010) was a multi-year event notable for causing persistent shifts in the relationship between rainfall and runoff in many catchments. Here, we describe a multi-disciplinary eWorkshop held in late 2020 to discuss the hydrology of the Millennium Drought and explore the hydrological processes leading to the hydrological shifts. Research to date has successfully characterised where and when shifts occurred, explored which catchment attributes are statistically related to the shifts, and noted changes in rainfall partitioning. However, a physical explanation for the changes in catchment behaviour is still lacking, hence the need for this workshop.
Integrating perspectives from hydrogeology, ecohydrology, remote sensing, hydroclimatology, experimental hydrology and hydrological modelling, the workshop aimed to share and discuss “perceptual models” of flow response that could explain the Millennium Drought streamflow observations, considering both the spatial and temporal patterns of hydrological shifts. We considered a range of perceptual models of flow response, and then evaluated the models against available evidence. The models consider climatic forcing, vegetation, soil moisture dynamics, groundwater, and anthropogenic influence. Perceptual models were assessed both temporally (e.g. why was the Millennium Drought different to previous droughts?) and spatially (e.g. why did rainfall-runoff relationships shift in some catchments but not in others?).
The results point to the unprecedented length of the drought (10+ years) as the primary climatic driver, paired with interrelated groundwater processes: declines in groundwater storage, reduced recharge associated with vadose zone expansion/drying, and reduced connection between subsurface and surface water processes. An additional contributor is increased evaporative demand, and minor contributors may include farm dams, salinity recovery, and drainage via regional groundwater systems. The roles of deep-rooted vegetation, wildfire, rainfall patterns, and land use change, among others, were discounted on various grounds.
There is a need to confirm these landscape-scale evaluations with local long-term field monitoring, particularly of subsurface dynamics, faced with a lack of such monitoring during the drought itself. A decline in monitoring meant that many variables went unmeasured that could have aided diagnosis. Thus, the drought provides an example to other countries of the value of continued investment, particularly to build up and retain multi-decadal records in as many sites and variables as possible. We strongly recommend investment in understanding of hydrological shifts through such monitoring, which is particularly important given the relevance of hydrological shifts to water planning under climate variability and change.
How to cite: Fowler, K., Peel, M., Peterson, T., Saft, M., and Nathan, R. and the additional coauthors listed below: Explaining rainfall runoff changes associated with the Millennium Drought, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12742, https://doi.org/10.5194/egusphere-egu22-12742, 2022.
Global change has different effects on inland water bodies. In the case of lakes, the water level is a variable frequently affected. Lakes in semi-arid zones are susceptible to climatic and anthropic forcing. Understanding how these factors modulate changes in lakes is essential to develop forecasts and generate management and conservation programs. However, lakes evolution under external forcing may differ despite belonging to the same system. The differences highlight the importance of developing particular management plans for each lake. Therefore, it is necessary to understand the factors that modulate these peculiarities. An example in central Mexico is the six maar lakes found in the easternmost basin of the Mexican Plateau, the Serdán Oriental Basin: Alchichica, Quechulac, La Preciosa, Atexcac, Tecuitlapa, and Aljojuca. Groundwater flow is essential in the water balances of these lakes. However, intensive groundwater exploitation for agriculture has occurred since the '80s in this semi-arid basin. Several studies have revealed that these lakes' trophic states, biota, and chemical compositions differ remarkably. Both locals and researchers have noted water-level declines in all lakes in recent decades. Water level evolution also seems to be particular in each lake. Data on the lakes water levels from 1960 to 1992 and subsequent changes are analyzed. We assessed physical (e.g., climatic, geological, hydrogeological, vegetation) and anthropic (land-use changes and groundwater exploitation) factors that could modulate the water level evolution differences. Time series analysis, remote sensing, and statistical methods were applied. This work represents a conceptual framework for further studies oriented to the numerical modeling of the lake system and the exploration of future change scenarios.
How to cite: Silva Aguilera, R. A., Escolero, O., and Alcocer, J.: Long-term differential water level responses of a group of tropical maar lakes in a semi-arid basin (Cuenca Serdán Oriental, México), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11088, https://doi.org/10.5194/egusphere-egu22-11088, 2022.
With great changes, such as climate and land use/cover, occurring in hydrological processes over the last decades, runoff sensitivity, here defined as proportional changes in runoff caused by a given proportional change in its driving factors, has also been changing over time. However, few studies have focused on this sensitivity change, and runoff sensitivity is always considered to be constant in runoff attribution analysis with an elasticity-based method. In this study, we attempt to examine the temporal variation of runoff sensitivity in the middle reaches of the Yellow River basin, China, and quantify its effects on the changes in runoff so that the existing attribution method can be improved. We found that runoff sensitivity showed statistically significant trend, and runoff became more sensitive to changes in climate and catchment characteristics (CC). CC, largely affected by land use/cover change resulting from large scale ecological projects, was the major contributor to change in runoff sensitivity, followed by precipitation, and lastly potential evapotranspiration. Runoff sensitivity variation contributed approximately 20% to the proportional runoff change, and by allowing runoff sensitivity to change over time, relative contributions of climate and CC to runoff would range from − 5.05% to 9.94%. Our study supplements research focusing on hydrological changes and interactions, and we suggest that temporal variation in runoff sensitivity should be considered when quantifying the impacts of driving factors on changes in hydrological processes.
How to cite: Wang, Y.: Runoff sensitivity variation should be incorporated in hydrological analysis, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1295, https://doi.org/10.5194/egusphere-egu22-1295, 2022.
Since the middle of the last century extreme rainfall events have intensified in many parts of the world (Martel et al., 2021), and increasing temperature is considered to let this development continue in the next decades. The Clausius-Clapeyron relationship, i.e. an about 7% increase per additional degree centigrade, yields an order of magnitude of what to expect, with convective rainfalls being likely to grow in a still more pronounced manner (Martel et al., op.cit.). Convective cells are, typically, associated with rainfalls of short duration and small spatial extent, which makes them particularly important for microcatchments.
Combining Green-Ampt type infiltration with kinematic overland flow, the relationship between a square-topped hyetograph and runoff is modelled. Frequently, design rainfall duration is chosen equal to the time of concentration. In case of an infiltrating surface, however, maximum peak runoff may result from shorter rainfall. There may, thus, be partial area runoff only, in which case the Schmid (1997) design storm equation yields the critical rainfall duration needed to determine maximum peak flow.
The study started from a chosen present-day IDF relationship of 20 years' return interval in Austria and a (rectangular) grass plot (hillslope) of 50 m length, 10% slope and an initial loss of 0.5 mm. Simulations were made using soil data from Columbia sandy loam, Guelph loam and Ida silt loam, in turn. Rainfall was assumed to be subject to Clausius-Clapeyron scaling and variable warming between 0.0 and 2.0 K.
In the case of the most pervious soil of the three (Columbia sandy loam, vertical saturated permeability Ksv = 0.0139 mm/s) flow was laminar and described by the Dary-Weisbach friction law (K = 4000). Contributing area remained small throughout (length 0.9 m for 0 K and 8.3 m for 2 K temperature increase). Corresponding peak flow showed above-linear growth and increased strongly from 0.013 L/(s.m) for 0 K to 0.17 L/(s.m) for 2 K.
The 'medium' soil, Guelph loam (Ksv = 0.00367 mm/s), was associated with contributing hillslope length growing from 35 m to the full 50 m as temperature increase varied from 0 to 2 K. Corresponding peak flows increased from 0.69 to 1.16 L/(s.m), i.e. by 68%. Flows over Guelph loam and Ida solt loam were turbulent (Manning's n = 0.4).
In case of the finest soil, Ida silt loam (Ksv = 0.000292 mm/s), all of the microcatchment contributed to overland flow from the start (DT = 0 K). Peak flow increased almost linearly with temperature from 2.31 to 2.77 L/(s.m), i.e. by 20%.
Consequently, it may be concluded that a future rise in temperature up to 2 K is likely to trigger strong increases in peak flows from infiltrating microcatchments. The present study indicates that Clausius-Clapeyron rainfall scaling may result in peak flows increasing much in excess of the 7% / K.
Martel, J.-L. et al.: Climate change and rainfall intensity-duration-frequency curves: overview of science and guidelines for adaption. J. Hydrol. Eng. 26(10), DOI: 10.1061/(ASCE)HE.1943-5584.0002122, 2021.
Schmid, B.H.: Critical rainfall duration for overland flow from an infiltrating plane surface. J. Hydrol. 193, 45-60, 1997.
How to cite: Schmid, B.: On climate change affecting the dynamics of overland flow from infiltrating microcatchments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2033, https://doi.org/10.5194/egusphere-egu22-2033, 2022.
This study tends to attribute the spatial patterns of hydrologic alteration in mid-latitude montane basins to the key driving forces being the climate and land use change. Physically-based distributed modeling system MIKE SHE was used for the analysis of changing spatiotemporal patterns of extreme runoff processes in montane catchments by using time series of hydrometeorological observations, and spatially distributed MODIS data for evapotranspiration (ET) and leaf area index (LAI) as key resources for the model setup.
Czech Republic is surrounded by mountain ranges from all sides but the southeastern border, which is drained towards the Danube. Due to this concentric orientation of topography each mountain range has different aspect and exposition due to atmospheric processes. Does the basin hydrological reaction on changing the environment depend on the aspect or is there an overall trend present in all basins? In order to answer such a question, it is necessary to understand the main drivers of changes and to quantify the effect of each separately.
8 headwater basins were analyzed of average size of 73 km2 where significant trends of hydrologic processes were detected from long-termed time series (1952 to 2018). Some of the trends are common for all basins such as seasonal shift of snowmelt period but other trends are rather site specific such as frequency of peak flows. Previous studies show that the hydrologic reaction on climate signal is the most dominant driver of the hydrologic alterations however there are other drivers such as forest disturbances that can mislead the interpretation of trend behavior.
The aim of the study was to separate the effects of those main drivers by a detailed distributed physically-based modeling system MIKE SHE. Input data originated from official and publicly available sources in order to design a methodology that could be reproduced in other basins of comparable properties. Models are bent together thus results of similar spatial-temporal quality were obtained for further analysis. Stational data but also remote sensed data in the grid format were gathered in a comprehensive database.
Two groups of scenarios were applied. First group was focused on climate signals (namely trends in precipitation, mean daily temperature and potential evapotranspiration) and the second group included land use changes such as bark beetle outbreak. Effect of both groups was quantified and compared with baseline simulation across all basins.
The model proved the long-term shifts in runoff seasonality, driven by the air temperature rise, and apparent across the mountain ranges. The seasonal runoff changes are marked by the shift of spring snowmelt toward an earlier season and a decline in spring flows. The second aspect of the changing seasonality is an earlier and prolonged period of summer low flows.
The results proved the dominancy of climate change as a main factor of runoff alteration, acting in large scale patterns, despite the local variations in physiography and land use.
How to cite: Bernsteinová, J. and Langhammer, J.: Attributing the spatial patterns of hydrological change to the effects of climate and land use change by distributed modelling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7753, https://doi.org/10.5194/egusphere-egu22-7753, 2022.
The land use and land cover (LULC) change induces hydrologic variability in a catchment and studying this variability is central to efficient water management practice in a catchment. The assessment of the alteration in hydrological processes due to LULC change and its influence on overall river ecosystem functioning is even more pertinent to developing nations that face the issue of water scarcity and pollution. In this work, we investigate the influence of the LULC change over a period of ~40 years (1970-2013) on the variability of natural or virgin flow in the Ramganga river, a major tributary of the Ganga river, India. For LULC change data, object-based image classification was performed on high-resolution satellite imageries acquired for the Ramganga river basin – CORONA (1970) and LISS IV (2013) images. The natural or virgin flows (i.e., the flow in the river without regulation practices such as construction of dams or barrages) were estimated by performing hydrological modeling using the Soil and Water Assessment Tool (SWAT). Initially, the SWAT model was set up, calibrated, and validated for the present flow scenario (i.e. with all management practices present) using LULC data of the year 2013. Natural flows were derived by removing all interventions and keeping agricultural practices only rain-fed. Next, keeping all parameters unchanged, the LULC data of the year 2013 was replaced by the LULC data of the year 1970. This enabled us to study the effects of LULC change on river hydrology between the period 1970-2013. The model showed good agreement between the observed and simulated flows with R2 values of 0.82 for the calibration period (2002-2014) and 0.68 for the validation period (1990-1999). The Nash-Sutcliffe efficiency values were 0.81 and 0.66 for calibration and validation periods respectively. The comparison of LULC data between the study period (1970 and 2013) reveals that land cover classes of agriculture, built-up, mixed forest, barren land, shrubs and bushes, and water areas were altered by nearly 6%, 102%, -7%, -59%, -75%, and -2% respectively (‘-’ sign indicates decrement in the land cover area). The influence of this LULC change was evident in the results from the hydrological model. For the years 2002-2013 (calibration period), the natural flows estimated using the LULC map of 2013 at the basin outlet were observed to be higher by 3-12% compared to flows estimated using the LULC input of 1970. The estimates of mean monthly flows for the years 2002-2013 at the basin outlet reveal that while the natural flows estimated using the LULC map of 2013 were higher compared to flow estimates using the LULC map of 1970 for most of the months, the flows during the dry months (May-July) were observed to be lower for the former compared to the latter. Our work provides valuable insights into hydrological variability in a major sub-basin of the Ganga river induced due to LULC changes and we advocate that alterations associated with LULC must be incorporated into water management strategies.
How to cite: Shrivastava, S., Gurjar, S., Suryavanshi, S., and Tare, V.: Influence of land use and land cover change on natural flow variability: a case study of river Ramganga, India, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11952, https://doi.org/10.5194/egusphere-egu22-11952, 2022.
Accelerated climate and land use land cover (LULC) changes are anticipated to have large impacts on water resources in the Colorado River Basin (CRB). Since land use is a result of complex socio-ecological factors, accurately predicting future patterns of LULC is challenging. In addition, substantial differences among a large number of climate models necessitate a screening process for impact and adaptation studies. As a result, limitations of conventional ‘top-down’ approaches are becoming increasingly apparent. More recently, ‘bottom-up’ assessments are gaining popularity for exploring climate and LULC conditions using a few selected cases that consider a range of possibilities. Here, we improved and employed the Variable Infiltration Capacity (VIC) model to generate streamflow projections across the CRB under multiple cases of climate and LULC changes. We integrated advances in the model using Landsat- and MODIS- based products to produce more realistic land surface conditions. Meteorological datasets were drawn from statistically downscaled projections (2006-2099) to represent ‘hot and dry’ and ‘warm and wet’ futures. Vegetation parameters were modified by using regional projections of a LULC model upon which more drastic disturbances were applied to forest cover types. Water managers in the CRB were consulted to ensure that a range of views were captured in the modeled storylines and to maximize the legitimacy and credibility of the research for decision-makers. Analyses were conducted to identify system vulnerabilities and unexpected outcomes that pose the greatest consequences to long-term water supplies in the CRB. Results indicated that forest disturbances partially offset warming effects to streamflow (basin-wide mean annual streamflow was up to 9% larger than the case without disturbance by end of century), allowing more neutral impacts under warming.
How to cite: Whitney, K., Vivoni, E., Wang, Z., and Mascaro, G.: Assessing Future Climate and Land Use Impacts to the Colorado River using a Bottom-up Modelling Approach Informed by Water Managers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5757, https://doi.org/10.5194/egusphere-egu22-5757, 2022.
The Valencia Anchor Station (VAS) is an Earth Observation super site run by the University of Valencia, where a fair number of satellite remote sensing missions are validated. Within the framework of the Joint ESA-EUMETSAT “OLCI Land Validation (OLCI-Land-Val)” project, and of the Joint Research Center Ground-Based Observations for Validation (GBOV) of Copernicus Global Land Products, the Climatology from Satellites Group (GCS) has installed a total of 16 FAPAR (Fraction of Absorbed Photosynthetic Active Radiation) stations over a large vineyard area, where the GCS has carried out an extended number of field campaigns following the vine phenological cycle to validate the relevant parameters related to chlorophyll and N2 content, LAI (Leaf Area Index), surface temperature and soil moisture together with the Sentinel-3-A and -B more OLCI-specific products OLCI FAPAR and OTCI (OLCI Terrestrial Chlorophyll Index).
This presentation shows the work carried out from the design and assembly of the FAPAR fixed stations, and the data series processed for the entire study period (2016-2021), to the different observations and validations carried out during the intensive observation campaigns. carried out in the area. Specifically, the data collection carried out consists of measurements using the SPAD 502 Plus Chlorophyll Meter which instantly measures the chlorophyll content or “greenness” of the plants, and whose calibration is carried out by means of cold extraction in the laboratory. These measurements are also used for the validation of the OTCI product obtained from Sentinel-3, as well as for its correlation with the continuously measured FAPAR and with the corresponding Sentinel-3 OLCI FAPAR product. Additionally, LAI data are included to establish the vegetation cover as well as soil moisture content and radiative surface temperature as a reference for the hydric stress conditions suffered by the vegetation.
At the same time, a study of the vegetation cover has been carried out on the study area using the products MCD15A3H, MCD12Q1-2 and MOD-MYD13, to establish a soil correction of the data collected at the plant level.
This leads to results where FAPAR and chlorophyll can be observed at three different levels, namely, in-situ plant, in-situ 300m x 300m with correction for the influence of the soil and satellite data. This research is important as a starting point in the validation of new indices with greater physical foundation and as confirmation of the robustness of the sensors on board the Sentinel 3-A, -B satellites for the continuity of the programme.
How to cite: Albero-Peralta, E., Lidón, A., Bautista, I., Lull, C., Asensi, V., and López-Baeza, E.: Validation of Vegetation Biophysical Parameters at the Valencia Anchor Station in the Framework of Copernicus Sentinel-3 OLCI, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12188, https://doi.org/10.5194/egusphere-egu22-12188, 2022.
The landscape of south-central Chile, originally a mosaic of pristine native forests and crops, has been converted into tree plantations and agroindustry. Farmlands and native forests have undergone a rapid conversion to fast-growing non-native pine and eucalyptus plantations, as well as irrigated fruits production for international exports. These two drivers have severely transformed the socio-ecological system, resulting in less biodiversity, more erosion, emigration and work depence, less drinking water, and a fire-prone landscape. A participatory approach helps not only to visualise tensions in the territory, but it is also useful for stakeholders to explore the possible environmental futures. However, frequently the development of land-use scenarios is mostly based on the views of experts and policymakers, missing out a wealth of local knowledge about the environment which experts seek to comprehend.
This work aims at quantifying the impacts of the aforementioned land cover changes in water provision for the population and ecosystems, by incorporating the views of the people that still live in a drought-prone rural area in the construction of different narratives representing future land management scenarios. The study area is the Cauquenes River Basin, a mediterranean catchment located in central Chile, historically known for wine production and rainfed agriculture. To develop the narratives, we conducted semi-structured interviews to collect and analyse qualitative information using a coding system systematised in the Atlas.ti software. Using 2050 as the simulation target year, narratives gave us the guidelines to develop the spatial scenarios. Then, using an open-source land use change model- called CLUE-s we constructed scenarios of future land use change. The CLUE-s algorithm allocates land uses based on the suitability of each land use as well as spatial regulations. To assess the impact on water provision of each scenario, they were evaluated using a hydrological model (SWAT+).
Our results identified two different narratives: i) rural development: where water availability could increase, if a protection strip is established near water courses, that is, scrublands and native forest are assigned in these areas and, rainfed agriculture is strengthened and reach the extension it had in 1990 and ii) agro-industrial development, in which the central government promotes irrigated agriculture for international export markets, at the same time, passive preservation plans for protect native forest are applied according to the current forestry regulation. We expect that this participatory approach will enrich and strengthen adaptive management capacity at the local level, to be able to face the challenges ahead presented by a drier future.
How to cite: Grau-Neira, A., Manuschevich, D., Galleguillos, M., Zambrano-Bigiarini, M., and Marinao, R.: Assessment of water provision under different future land use scenarios in the Cauquenes Catchment, Chile. , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8141, https://doi.org/10.5194/egusphere-egu22-8141, 2022.
Mon, 23 May, 10:20–11:50
Chairpersons: Sina Khatami, Margarita Saft, Keirnan Fowler
Among the properties that a wise modeler would desire for his or her own model is the capacity of extrapolation beyond known hydroclimatic conditions. Extrapolation capacity seems essential when a model is to be used to predict the impact of future conditions, which may not have occurred in the past (at least not during the calibration period). Hydrological good sense would let us imagine that the more complete the model, the better it should do in extrapolation. But because the wise should doubt even one’s good sense, we wish to test this hypothesis, starting with a series of extremely simple models, working at the annual time step:
- the simplest of all annual models is a linear one, using only annual precipitation Pn as explanatory variable: Qn = a.Pn +b (Qn being streamflow for year n, a and b being calibrated parameters);
- slightly more complex is a three-parameter linear model using both precipitation Pn and potential evaporation En as input: Qn = a.Pn +bEn + c;
- slightly more complex is a non-linear model based on the Turc-Mezentsev formula (Andréassian & Sari, 2019);
- again, more complex is a non-linear model based on the Catchment Forgetting Curves (CFC) accounting for the pluriannual catchment memory (de Lavenne et al., in review);
- last, we use a much more complex daily time step hydrological model as reference.
To answer our title question, we test the robustness of these models of increasing complexity using a dataset of 555 French catchments, a specific metric (PMR - Royer-Gaspard et al., 2021) and the robustness assessment test (RAT - Nicolle et al., 2021).
Andréassian, V. and Sari, T.: Technical Note: On the puzzling similarity of two water balance formulas – Turc-Mezentsev vs Tixeront-Fu. Hydrol. Earth Syst. Sci., 23, 2339-2350, 2019.
de Lavenne, A., Andréassian, V., Crochemore, L., Lindström, G., and Arheimer, B.: Quantifying pluriannual hydrological memory with Catchment Forgetting Curves, Hydrol. Earth Syst. Sci. Discuss. [preprint], in review, 2021.
Nicolle, P., Andréassian, V., Royer-Gaspard, P., Perrin, C., Thirel, G., Coron, L., and Santos, L.: Technical note: RAT – a robustness assessment test for calibrated and uncalibrated hydrological models, Hydrol. Earth Syst. Sci., 25, 5013–5027, 2021.
Royer-Gaspard, P., Andréassian, V., and Thirel, G.: Technical note: PMR – a proxy metric to assess hydrological model robustness in a changing climate, Hydrol. Earth Syst. Sci., 25, 5703–5716, 2021.
How to cite: Santos, L., Royer-Gaspard, P., de Lavenne, A., and Andréassian, V.: Are simpler models less robust?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8434, https://doi.org/10.5194/egusphere-egu22-8434, 2022.
We studied the effect of a 13-year long dry period on the performance of five conceptual rainfall-runoff models in 155 catchments in the Australian state of Victoria in order to identify (1) which aspects of the flow regime are harder for models to reproduce during and after the drought; and (2) how model performance during this persistent drought compares to that during similarly dry individual years in the historical record. Persistent dry conditions in recent decades have affected hydrological processes and water partitioning in several regions globally; given the increased risk of drought posed by climate change, studying these historical long-lasting droughts and their effects on model reliability can inform climate adaptation strategies in many drought-prone regions worldwide.
The Millennium drought (MD), which affected more than 1×106 km2 of south-eastern Australia between 1997-2009, is one of such events and arguably the most reported on in literature. Research to date identifies significant shifts in catchment-level annual rainfall-runoff relationships in most catchments affected by the MD, many of which have failed to recover several years after the end of the meteorological anomaly. These shifts affect the reliability of models’ projections; however, by focusing on a handful of performance metrics only, currently published research falls short on identifying which specific aspects of model performance are affected and how.
Here, we focused on a wider range of performance metrics to assess models’ ability to represent a variety of aspects of the hydrograph and the flow-duration curve during and after the MD. For objective (1), we used a statistical metric derived from Wilcoxon signed-rank test (known as matched-pairs rank-biserial correlation coefficient) to compare changes in model performance during and after the drought from a pre-drought benchmark across metrics and catchments. For objective (2), we analysed changes in the relationship between annual model performance and annual rainfall using a regression technique.
We observed extensive degradation of model performance during the drought across most of the metrics studied. Overestimation of flow volumes drives the decline, while representation of shape and variability of the hydrograph and the flow-duration curve are more resilient to prolonged drought. This means that volumes’ overestimation is not associated to specific flow regimes, but results from flow declining proportionally throughout the hydrograph, suggesting that multiple catchment processes interact to cause the observed changes across high and low flows as well as through faster and slower routes. We obtained very similar results in the decade after the drought, indicating that model performance, similarly to rainfall-runoff relationships, often does not recover after the dry spell ends. Additionally, regression analysis of annual performance and rainfall showed disproportional decline of model reliability during the multi-year event compared to single dry years before the drought, suggesting that the persistency of the drought is likely responsible for exacerbated performance decline due to accumulation and aggravation of errors over subsequent dry years.
How to cite: Trotter, L., Saft, M., Peel, M., and Fowler, K.: How does the performance of rainfall-runoff models degrade due to multi-annual drought? A large-sample, multi-model study., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6866, https://doi.org/10.5194/egusphere-egu22-6866, 2022.
The H2020 project DRYvER (https://doi.org/10.3897/rio.7.e77750) on drying river networks and climate change aims at understanding the impact of climate change on intermittent rivers and ephemeral streams in six mesoscale river basins between 200~km² and 350~km² in different European countries (Croatia, Czech Republic, Finland, France, Hungary, Spain).
One of the objectives of the DRYvER project is to compare the evolution of streamflow intermittence under climate change in the six study areas.
To do so we are developing a common modelling framework, using the distributed and physically based hydrological model J2000 (Krause et al., 2006), which is able to represent processes at the reach scale, and therefore, simulate flow intermittence at a high spatio-temporal resolution.
A challenge here is to use a climate forcing dataset (precipitation and temperature) that has a sufficiently large coverage to cover all the catchment case studies, but that also accurately represents the spatial and temporal variability of the meteorological variables in order to accurately simulate the local hydrological response.
In this study, we analyze the impact of using datasets with global or European coverage (ERA5-land, WFDE5, UERRA-MESCAN, E-obs) versus using local observed data or local gridded datasets (e.g. SAFRAN reanalysis for France, Nordic Gridded Climate Dataset for Finland).
First, we compare the climate datasets at the catchment scale, and then analyze the impact of using them on the simulated runoff.
Results show variable differences between the datasets for the six catchment case studies, with larger gaps in mountain basins with a larger range of elevations.
This work has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 869226.
How to cite: Mimeau, L., Künne, A., Kralisch, S., Branger, F., and Vidal, J.-P.: Inter-comparison of climatological datasets for the hydrological modelling of six european catchments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9782, https://doi.org/10.5194/egusphere-egu22-9782, 2022.
Evaluating likely hydrological consequences of predicted and current actual climatic change is a complex challenge, not only because of uncertainties about societal, land-use and vegetational responses and feedbacks, but also because lack of information on some climatic variables that influence hydrological processes. With a focus on the humid tropics, this paper addresses the influence of changes in rainstorm size-frequency on the interception component of evapotranspiration - and how this can in turn influences the nature and magnitude of impact of rainfall change on catchment water budgets. This is critical for two reasons. First, both climatic modelling predictions and current trends for annual rainfall in the humid tropics vary greatly between regions from significant increases to major declines. Second, because of the ability of a warmer atmosphere to hold more water vapour, IPCC confidently predicts that extreme rainstorms worldwide will increase regardless of annual rainfall trends and it is also arguable that rainstorms in general will increase in intensity and storm total. Thus changes in rainstorm size-frequency distribution are to be expected.
This paper focuses on the primary and disturbed equatorial rainforest environment of Sabah, Malaysian Borneo. The paper (1) uses long-term daily rainfall series at four stations in Sabah (from 1906 for Sandakan, Tawau and Kota Kinabalu; and from 1985 for Danum) to assess the magnitude of recent changes in rainstorm size-frequency distribution in Sabah and (2) presents and uses a simple Excel-based model to translate these data into estimated changes in interception (and also total evapotranspiration and river flow). The underlying principle of the model is that Interception (as a percentage of storm rainfall) falls with increasing storm size, as interception storage capacity is filled. Results of previous rainforest interception studies (including by one of the authors at Danum in Sabah) are used to calibrate the model, whereby percentage interception reduces in steps from 100 % for storms of < 1 mm and 80 % for storms of 1-2 mm, to 13.6 % for storms of 10-14.9 mm and the interception capacity of 2.2 mm (5.5 % or less) for storms of >40 mm. It follows that annual interception, both in mm and as a percentage of annual rainfall, will be much greater if most rainstorms are small, but progressively lower as the percentage of rain falling in big storms increases. Differences in rainstorm size-frequency distribution help to account for the big range (7-27 % of annual rainfall) in annual interception found between different rainforest locations. The Pico presentation first presents the model and demonstrates the magnitude by which simulated annual interception values vary between individual years of contrasting annual rainfall and rainstorm size-frequency distribution at the four locations. Then the temporal changes in daily rainfall size-frequency at the four stations are presented and compared and (using model outputs) changes in seasonal and annual interception and other water budget variables are assessed. Finally, problems with, possible improvements to, and the wider applicability of the approach adopted are discussed.
How to cite: Walsh, R., Bidin, K., Safjankova, A., and Nainar, A.: Modelling effects of changing rainstorm size-frequency on annual interception and catchment water budgets in Sabah, Malaysian Borneo, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12824, https://doi.org/10.5194/egusphere-egu22-12824, 2022.
Abstract: With its highly variable climate, Australia is naturally susceptible to multi-year droughts. Previous studies have shown that Australia will, in future, experience longer and more severe droughts, especially across southern Australia. Extended periods of drought have been associated with hydrological changes, in particular streamflow regimes including changes to the magnitude, frequency, duration, predictability or flashiness of streamflow (Kiem et al. 2016). Despite significantly impacting water availability across the world, links between multi-year drought effects on the hydrological responses of catchments and changing flow regimes are not well understood. This is an important issue since regime shifts from e.g., perennial to non-perennial, could be correlated to the variability in rainfall intensity and frequency, leading to changes in infiltration, excess overland flow and surface-subsurface connectivity.
Our study aims to assess the effect of multi-year droughts on the streamflow regimes to inform future water resource management. We classify historical and current dominant streamflow regimes across Australia and explore whether the susceptibility of stream networks to perennialism under multi-year drought periods is likely to increase in the future. We first use Victoria as a case study region to improve collective knowledge on non-perennial rivers; their drivers, flow regime patterns and frequency of occurrence using the Australian Bureau of Meteorology (BoM)'s long-term hydrologic reference stations and a range of streamflow-based indicators. We analyse pre-drought states of streamflow regimes and explore whether they have shifted after the Millennium multi-year drought. We also investigate the major climatological and hydrological drivers that affect streamflow regime shifts, with a particular focus on those catchments which have shown to have shifted rainfall-runoff relationships resulting from the Millennium drought.
Kiem, A. S., and Coauthors, 2016: Natural hazards in Australia: droughts. Clim. Change, 139, 37–54.
How to cite: Azarnivand, A., Bende-Michl, U., Sharples, W., and Bahramian, K.: Multi-year drought impacts on streamflow regimes , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9042, https://doi.org/10.5194/egusphere-egu22-9042, 2022.
As one of the world’s driest continents, Australia’s water resources need to be carefully managed to ensure sustainable access to water for livelihoods, human well-being, and ecosystem health. Australia is also a land of extremes from floods to droughts and catastrophic wildfires which are all becoming more frequent and destructive. It is essential to understand future changes in water availability and hydrologic extremes to support the development of mitigation strategies and the planning for water infrastructure and policies. To build this understanding, the Bureau of Meteorology has released the Australian Water Outlook (AWO), a seamless national landscape water service. The AWO includes National Hydrological Projections, as well as seasonal forecast and historical products, all using the Bureau’s Australian Water Landscape Water Balance model (awo.bom.gov.au).
Projection results feature many sources of uncertainty, including how future greenhouse gas emissions will develop, how a changing climate will lead to changes to hydrological features and feedback loops, and the climate and hydrological models used to simulate those changes. Acknowledging these uncertainties, the Bureau's National Hydrological Projections ensemble provides a unique opportunity to examine impacts of future changes on Australia’s hydroclimate and its water resources. It allows nationally consistent impact assessments across multiple spatial and temporal scales. To produce these projections, three bias-correction approaches were used as well as a regional downscaling model. These methods were in turn applied to four global climate models in an operational framework resulting in a nationally consistent future change dataset for climate (rainfall, solar radiation, temperature, and wind) and hydrological (soil moisture, evapotranspiration, and runoff) variables.
An overview of the National Hydrological Projections methods and results, including a series of 8 regional water resource assessment reports, will be presented. The reports were created to facilitate understanding and use of the data and describe future changes in regional hydrology using a novel storyline approach. The storyline approach is used to improve the communication of plausible impacts to Australia's future water availability. Plausible futures portend a drier climate for large parts of Australia which could pose challenges for future water resource management.
How to cite: Bende-Michl, U., Wilson, L., Sharples, W., Oke, A., Hope, P., Matic, V., Turner, M., Khan, Z., Kociuba, G., and Carrara, E.: Assessing patterns of future hydrological change for Australia: insights from the National Hydrological projections , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6710, https://doi.org/10.5194/egusphere-egu22-6710, 2022.
In this study we investigated the impacts of climate change on a large nivo-glacial river basin (Naryn Basin) in Central Asia (Kyrgyzstan) using two different families of General Circulation Models (GCMs). Hence, we use the widely used ISIMIP2 (Inter-Sectoral Impact Model Intercomparison Project) data which is based on the GCMs of the 5th stage of the Coupled Model Intercomparison Project (CMIP5), as well as the newly derived ISIMIP3 data, which uses the latest GCM data from phase 6 of CMIP (CMIP6) to drive a hydrological model (Soil Water Assessment Tool - SWAT). As both sources of forcing (ISIMIP2 & ISIMIP3) show considerable differences in multiple aspects such as used GCM family, projections, bias-adjustment technique and reference dataset, we evaluate and compare the individual projected changes of both generations on different variables of the hydrological cycle, such as snowmelt, evapotranspiration and soil moisture. In order to quantify the uncertainty contribution of different components along the modelling chain we perform a sensitivity analysis using an ANOVA (Analysis of Variance) approach. Hereby, it is intended to reveal which source (CMIP phase, GCMs, scenario) can be attributed the largest contribution. Results show that significant differences in the impact assessment can occur depending on the
CMIP generation. It is also shown that the CMIP phase has a high contribution to the total uncertainty estimates. However, in a next step special ephasize is put on the improvement of nivo-glacial processes, which will be performed by an improvement of the hydrological model SWAT, by integrating a glacier module which accounts for not only for glacier mass balance changes but also considers glacier recession and to a limited degree potential advance.
How to cite: Schaffhauser, T., Lange, S., Tuo, Y., and Disse, M.: Change in Climate Impact Assessment from CMIP5 to CMIP6 in a High-Mountaineous Catchment of Central Asia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12551, https://doi.org/10.5194/egusphere-egu22-12551, 2022.
Climate change effects on the hydrologic cycle are a main concern for the evaluation of water management strategies. Climate models project important precipitation changes for the future, considering greenhouse emission scenarios. In this study, the EURO-CORDEX (European COordinated Regional Downscaling Experiment) climate models were first evaluated in a Mediterranean island (Sardinia), against observed precipitation for a historical reference period (1976-2005). A weighted Multi-Model Ensemble (ENS) was built, weighting the individual models based on their ability to reproduce observed rainfall. Future projections (2071-2100) were carried out, following the RCP-8.5 emissions scenario, to evaluate future changes in precipitations. ENS was then used as climate forcing for the SWAT model (Soil and Water Assessment Tool), with the aim to assess the consequences of such projected changes on streamflow and runoff of two small catchments located in the South-West Sardinia. Results showed that a decrease of mean rainfall values, up to -25 % at yearly scale, is expected for the future, along with an increase of extreme precipitation events. Particularly, in the eastern and southern areas, extreme events are projected to increase by 30%. Such changes reflect on the hydrologic cycle with a decrease of mean streamflow (-18% to -25%) and runoff (-12% to -18%), except in spring, when runoff is projected to increase by 20-30%. These results stress that Mediterranean is a hotspot for the climate change and the use of model tools can provide useful information to adopt water and land management strategies to deal with such changes.
How to cite: Marras, P. A., Lima, D. C. A., Soares, P. M. M., Cardoso, R. M., Daniela, M., Elisabetta, D., and Giovanni, D. G.: Climate change effects in a Mediterranean island and streamflow changes for a small area using EURO-CORDEX simulations combined with the SWAT model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-756, https://doi.org/10.5194/egusphere-egu22-756, 2022.
High and low flows are hydrological flow extremes threatening human being by causing floods and droughts. They are caused by meteorological extremes and human activities. Changes in meteorological conditions will inevitably impact the frequency of hydrological extremes and exacerbate their associated hydrological impacts.
This study focuses on modelling projected change in both frequency and magnitude of flow extremes as consequence to change in climate condition in the Siliana catchment in Tunisia. The SWAT and HBV hydrological models were calibrated using historical data and fed with an ensemble of high resolution CORDEX climate models. Results project a warmer and drier hydrometeorological conditions in the Siliana catchment. The precipitation is expected to decrease in the future by an average of 10% in dry season and 12% in wet season. In contrast, temperature is expected to increase by an average of +2°C in dry season and 1.8°C in wet period.
The two models show that while magnitude and frequency of high flows are expected to decrease, low flows frequency is expected to increase which affirms that the Siliana catchment is likely to experience severe hydrological conditions with reduction in water availability and increase in drought frequency.
How to cite: EL Ghoul, I., Tliha, F., Sellami, H., Mounir, K., Khlifi, S., and Vanclooster, M.: Climate change induced impacts on hydrological extremes at the catchment scale: case of Wadi Siliana (North western Tunisia), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8676, https://doi.org/10.5194/egusphere-egu22-8676, 2022.
Mediterranean ecosystems are commonly heterogeneous savanna-like ecosystems, with contrasting plant functional types (PFTs, e.g., grass and woody vegetation) competing for the water use. At the same time the structure and function of the vegetation regulates the exchange of mass, energy and momentum across the biosphere-atmosphere interface, influencing strongly the soil water budget. Mediterranean regions suffer water scarcity due to (in part) natural influences, i.e., climate changes. Future climate scenarios are predicting further warmer conditions, increasing the uncertainty on the future of the water resources system of these regions.
The objective is to investigate the role of the PFT vegetation dynamics on the soil water budget of a typical water-limited Mediterranean ecosystem in Sardinia, Italy, for both past and future climate conditions. The Sardinian site is characterized by strong heterogeneity, with wild olive trees coexisting dynamically with grass and bare soil, and a long database of land surface data is available from 2003, when an eddy covariance based tower was installed for estimating evapotranspiration, CO2 exchanges and energy fluxes. Sap flow of the wild olives (both in the trunk and in the roots), soil moisture, and leaf area index (LAI) are also measured. In water-limited conditions trees survive absorbing water from underlying fractured bedrocks through roots (hydraulic redistribution, HR). An ecohydrological model, based on the coupling of a land surface model (LSM) and a vegetation dynamic model (VDM) predicted the soil water balance, the tree and grass LAI, HR, and the dynamics of this sensitive ecosystem. The model was successfully tested for the case study, demonstrating model high performance for the wide range of eco-hydrologic conditions.
Interestingly, from 2003 tree cover increased reaching an almost constant LAI (around 4) after six years, but the tree cover dramatically decreased in the last 4 years due to a dramatic drought in 2017, which significantly affected the tree sustainability. Indeed, the winter precipitation decreased in Sardinia, with a concomitant increase of air temperature during the spring and summer seasons. Future climate scenarios predicted a further increase of air temperature and, therefore, of vapor pressure deficit (VPD), and a decrease of winter precipitation with a concurrent increase of rain extremes. We used the future climate scenarios predicted by Global climate models (GCM) in the Fifth Assessment report of the Intergovernmental Panel on Climate Change (IPCC). Hydro-meteorological scenarios are generated using a weather stochastic generator that allows simulation of hydrometeorological variables from GCM future scenarios. The use of the calibrated VDM-LSM allow to predict soil water balance and vegetation dynamics for the generated hydrometeorological scenarios. Results demonstrate that tree dynamics are strongly influenced by the inter-annual variability of atmospheric forcing, with tree density changing according to seasonal rainfall. At the same time the tree dynamics affected the soil water balance. We demonstrated that future warmer scenarios will impact wild olive trees, which could be not able to adapt to the increasing droughts. The decrease of tree cover will affect water resources and carbon balance of the heterogenous Mediterranean ecosystem.
How to cite: Chessa, C., Corona, R., and Montaldo, N.: Past and Future Climate Change Impacts on the Sustainability of a Wild Olive–based Heterogenous Ecosystem in Sardinia , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11233, https://doi.org/10.5194/egusphere-egu22-11233, 2022.
Changes in climatic forcing will change regional hydrological responses, both long-term seasonal dynamics and extreme events. Impact assessments are urgently needed by decision makers for climate adaptation planning, despite the uncertainties in the impact model chain. Therefore, uncertainties in impact assessments need to be evaluated and communicated along with the actual results in a transparent and user-friendly way.
Here, we show results from a hydrological climate impact study for Sweden, which is communicated to regional planners through a web-based assessment tool (smhi.se/en/climate/future-climate/advanced-climate-change-scenario-service/hyd). Climate change impacts are expected to alter seasonal hydrological dynamics as well as hydrological extremes in the region. We use a modelling framework based on a calibrated national hydrological model, S-HYPE, which divides the domain into ~ 35000 computational sub-basins, for which hydrological states and fluxes are computed using a conceptual process model including lake and river management routines. S-HYPE is forced with an ensemble of Euro-CORDEX regional climate forcing for a 1971 to 2100 assessment period and representative concentration pathways 2.6, 4.5, and 8.5. All forcing is bias-corrected to a gridded reference forcing data set using quantile mapping. Results are communicated in a spatially aggregated form for ~ 250 river basins using climate impact indicators (CII), which highlight expected change patterns for specific parts of the hydrolgical cycle, e.g. change in maximum annual snow water equivalent or summer discharges. Uncertainties are communicated through ensemble spread and robustness measures, allowing users to directly assess at least parts of the uncertainty in the model results.
We also use the modelled results for a comparative analysis of change impacts across river basins in Sweden, taking advantage of the north-south climate gradient across the domain. This allows for a direct comparison of modelled today and future behaviour of similar river basins across that gradient to evaluate the uncertainty in future impacts which orginate in the model representation of interactions and feedbacks between climate and hydrological system within the S-HYPE model framework.
How to cite: Capell, R., Musuuza, J., Berg, P., Bosshard, T., and Lindström, G.: Regional hydrological response to climate change across Sweden - impact modelling and communication, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8143, https://doi.org/10.5194/egusphere-egu22-8143, 2022.
Typically, the future hydrological behavior of a river basin, for example as a result of climate change, is predicted using hydrological models calibrated with historical observations. In reality, hydrological systems, and hence model parameters, experience almost continuous change in time and space. More specifically, there is growing evidence that vegetation adapts to changing conditions by adjusting its root-zone storage capacity, i.e. the amount of water in the unsaturated subsurface which is available to the roots of vegetation for transpiration. Additionally, other species may become dominant under natural and anthropogenic influence. In this study, we test the sensitivity of hydrological model predictions to changes in vegetation parameters that reflect ecosystem adaptation to climate and potential land-use changes. In other words, if the climate changes, how should our models change and what is the effect on the hydrological response? Our methodology directly uses projected climate data to estimate how vegetation adapts its root-zone storage capacity at the catchment scale to changes in hydro-climatic variables and potential land-use change. We test the hypothesis that changes in the hydrological response under global warming are more pronounced when explicitly considering changes reflecting adaptation of the root-zone storage capacity of vegetation. We compare a stationary benchmark model with several non-stationary model scenarios reflecting climate and potential land-use changes in the Meuse basin. We found that the larger root-zone storage capacities (+34%) in response to warmer summers under projected +2K global warming result in up to -15% less streamflow in autumn due to up to +14% higher summer evaporation in the non-stationary scenarios compared to the stationary benchmark scenario. By integrating a time-dynamic representation of changing vegetation properties in hydrological models, we make a potential step towards more reliable hydrological predictions under change.
How to cite: Bouaziz, L. J. E., Aalbers, E. E., Weerts, A. H., Hegnauer, M., Buiteveld, H., Lammersen, R., Stam, J., Sprokkereef, E., Savenije, H. H. G., and Hrachowitz, M.: Sensitivity of hydrological predictions to ecosystem adaptation in response to climate change: the effect of time-dynamic model parameters, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4613, https://doi.org/10.5194/egusphere-egu22-4613, 2022.
Climate change impact on floods and water resources is crucial for planning adaptation strategies. This is especially true in Mediterranean regions where a decrease in precipitation and an increase in extreme rain rates are projected. Global climate models and common hydrological models are often too coarse to represent rainfall properties and hydrological processes in these regions due to their scale. Therefore, the current understanding of climate change's impact on hydrological properties and processes in Mediterranean catchments is missing. To resolve this, we utilize the high-resolution (1 km2) weather research and forecasting (WRF) model (abstract #EGU22-1996). Rainfall simulations were input to a distributed hydrological model (<60 s, 100 m2 GB-HYDRA). Explicitly, we apply spatially-shifted ensemble results for 41 couples of heavy precipitation events in historic (end of 20th century) and future (end of 21st century; RCP 8.5 scenario) climate conditions to 4 small-medium-size basins (18–69 km2) in the eastern Mediterranean. Ensemble average total precipitation decreased by 24% between historic and future events. This resulted in an average decrease in outlet peak discharge (-20%, non-significant), and a significant drop in the total flood volume (-27%) in future events. This change can be attributed to a significant (-25%) decrease in runoff contributing area (RCA); hillslope sections from which water flows, reaches the stream network, and consequently, the basin outlet and significant decrease of the averaged rainfall rates over them (-22%). The results of this study suggest that ongoing climate change in Mediterranean regions is expected to have a considerable impact on the flow regime, and thus, practical actions should be taken.
How to cite: Rinat, Y., Armon, M., and Morin, E.: The effects of global warming on flood properties in small-medium Mediterranean catchments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4777, https://doi.org/10.5194/egusphere-egu22-4777, 2022.
Global bias-adjusted daily climate projections have been recently set up as part of the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP) phase 3 based on CMIP6 projections (Lange et Büchner., 2021). This dataset is aimed at being used as input to global hydrological models, and their coarse resolution however prevents them to be used for catchment-scale and reach-scale applications.
This work proposes to downscale these global climate projections through a pragmatic delta change approach and to derive catchment-scale streamflow time series through a fully-distributed hydrological model. The final objective is to produce future daily streamflow series over a high-resolution hydrographic network of 6 European catchment case studies for the DRYvER project (Datry et al., 2021). The advanced delta change approach (van Pelt et al., 2012) is selected here as it allows to create differential change factor according to distribution quantiles. The method is applied on precipitation, temperature, and potential evapotranspiration serving as input to the distributed JAMS-J2K model (Krause et al., 2006).
This setup is first applied to the Ain catchment case study (France) that includes the intermittent Albarine river, considering a control period (1985-2014) and two future periods (2021-2050 and 2071-2100). These experiments are conducted using one run from 5 different global climate models and 2 emission/socio-economic scenarios (SSP1-RCP2.6 and SSP5-RCP8.5) from the CMIP6 experiments. This methodology allows to grasp the range of future changes in daily streamflow over the entire catchment. The comparison between the control period and the two future periods is used to describe possible changes over seasonal discharge and low flow characteristics.
This approach is a preliminary step providing first and rapid insights into plausible futures for European intermittent rivers in terms of hydrology, biodiversity, ecosystem functioning and services, and adaptive management. Future steps will refine such futures using an innovative downscaling approach combining global and catchment-scale transient projections way to better grasp the joint influence of climate change and climate variability on reach-scale intermittence.
This work has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 869226
Datry et al. (2021) Securing Biodiversity, Functional Integrity, and Ecosystem Services in Drying River Networks (DRYvER). Research Ideas and Outcomes. https://doi.org/10.3897/rio.7.e77750.
Krause et al. (2006) Multiscale investigations in a mesoscale catchment: hydrological modelling in the Gera catchment. Advances in Geosciences. doi:10.5194/adgeo-9-53-2006.
Lange et Büchner (2021) ISIMIP3b bias-adjusted atmospheric climate input data (v1.1), ISIMIP Repository. doi:10.48364/ISIMIP.842396.1.
van Pelt et al., (2012) Future changes in extreme precipitation in the Rhine basin based on global and regional climate model simulations. Hydrology and Earth System Sciences. doi:10.5194/hess-16-4517-2012.
How to cite: Devers, A., Lauvernet, C., and Vidal, J.-P.: Using the advanced delta change approach and a distributed model for a rapid assessment of reach-scale streamflow projections in intermittent rivers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3950, https://doi.org/10.5194/egusphere-egu22-3950, 2022.
UN Sustainable Development Goal (SDG) 6.1 aims to achieve universal and equitable access to safe and affordable drinking water for all by 2030. However, even in a developed nation such as Scotland, climate change, and the water systems resilience to it, is putting achieving this goal at risk. Despite being abundantly blessed in terms of water resources, Scotland is facing an accelerated increase in the frequency of extreme weather events. The UK Climate Projections 2018 indicate that Scotland’s climate will become warmer, with drier summers, and increased occurrence of drought events. Recent water scarcity events prove the surge and are evidence for the projected weather patterns. Unlike drought indicators which are parameters describing meteorological, hydrological or agricultural drought conditions, like precipitation amounts, streamflow levels, soil moisture information, drought indices derive value based on statistical calculations. Once such meteorological drought index is the Standardised Precipitation and Evapotranspiration Index (SPEI) which is similar to the Standardised Precipitation Index (SPI). Unlike SPI, SPEI incorporates changes in evapotranspiration as it includes both precipitation and temperature as input data for calculation. Hence, SPEI makes a good choice for projecting future changes in a warming world and allows us to see the impact of climate change in inducing drought. Regional-scale analysis of SPEI across 36 sites using a 50 km grid generated drought scenarios for the longer term 2041-2080 using all 12 model members the UKCP18 dataset using 1981-2020 as the baseline period. These UKCP 18 projections were bias-corrected and downscaled to a 1km grid across Scotland before we acquired the data for analysis, thus enabling the calculation of SPEI at a finer scale. SPEI was then calculated at a 6-month timestep across the 36 sites in Scotland. The number of extreme drought months was computed for the baseline and the future periods. The drought month was defined as any month which has SPEI ≤ -2. After calculating the extreme drought months for baseline and future periods, the metrics from 1981-2020 were subtracted from the future period for each model member to demonstrate the amount of change in the number of drought months from the baseline period. Results were calculated separately for the individual member and not averaged to avoid incorporating uncertainty associated with projections. The majority of the sites across the spatial extent showed projected increases in the number of drought months for the future period for each of the model members. Sites in the southwest and western Scottish islands showed a greater increase compared to other sites where extreme drought months were observed with little or no change. Results highlighted the need for better preparedness for water scarcity situations which are going to be exacerbated by climate change.
How to cite: Pawar, S., Halliday, S., Glendell, M., and Ovando Pol, P.: What does the future hold? Using Standardised Precipitation and Evapotranspiration Index (SPEI) to project drought in Scotland. , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3707, https://doi.org/10.5194/egusphere-egu22-3707, 2022.
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