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Hydrological change: regional hydrological behaviour under transient climate and land use conditions

Estimates of water availability and flooding risks remain one of the central scientific and societal challenges of the 21st century. The complexity of this challenge arises particularly from transient boundary conditions: Increasing atmospheric greenhouse gas concentrations lead to global warming and an intensification of the water cycle and finally to shifts in the temporal and spatial distribution of precipitation and terrestrial water availability. Likewise, large-scale land use changes impact and alter regional atmospheric circulation, thereby local precipitation characteristics and again terrestrial water availability. Also the feedbacks between the interlinked terrestrial and atmospheric processes on different spatial and temporal scales are still poorly understood.
This session therefore invites contributions addressing past, present and prospective changes in regional hydrological behaviour due to either (or joint) climate- and/or land use changes. We especially welcome contributions on the development of novel methods and methodologies to quantify hydrological change. Further aspects of this topic comprise particularly:

- Robustness of hydrological impact assessments based on scenarios using downscaled climate model – hydrology model modelling chains.
- Quantification of regional land use change predictions and impact of past, present and future land use changes on water and energy fluxes in meso- to large-scale catchments.
- Joint or coupled modelling of water and energy fluxes between the atmosphere and the land surface/subsurface and analyses of feedback mechanisms.
- Climate change/land use change signal separation techniques and quantification of future land use change vs. climate change induced hydrological change.
- Adequate handling of climate change and land use change data and their uncertainty for the forcing of hydrological models.
- Case studies of regional hydrological behaviour in climate sensitive and flood or drought prone regions worldwide.

Convener: Stefan Hagemann | Co-conveners: Axel Bronstert, Harald Kunstmann, Rajib Maity
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Fri, 30 Apr, 11:00–12:30

Chairpersons: Stefan Hagemann, Axel Bronstert, Harald Kunstmann

Christoph Sauer et al.

Projections of the 21st century potential future climate evolution, especially for precipitation, are associated with high uncertainty and variability. Knowledge of the variability of the projected precipitation and resulting run-offs and the sources of uncertainties form the basis for analysis and assessment of future water-management options as well as potential risks related to droughts and flood events. The variabilities related to climate modelling can only be assessed by using a comparatively large number of climate projections.

In our research, we apply a large ensemble of regional climate model projections from the regional climate model REMO, driven by different global climate model simulations, at high temporal (hourly timestep) and high spatial (0.11 degree, or about 12.5 km) resolutions. Although the analysis of such big datasets involves considerable computational and storage capacities, this potentially helps to improve the simulation of future hydrological quantities in river catchments. For the analysis of the behaviour of small river catchments, we apply a semi-distributive hydrological model. Annual and winter average precipitation conditions show a robust and statistically significant increase especially for the RCP8.5 scenario. Precipitation ranges are compared with the ranges of runoff based on hydrological impact model runs driven by a set of simulated parameters from the regional climate model ensemble. The analyses are performed for a sub-catchment of the Lower Elbe system (Krückau catchment), which is a typical small basin (area < 200km2) close to the city of Hamburg in northern Germany. The model runs cover a long simulation period of 150 years (1950-2100) with a temporal resolution of 1 day. Short term model runs with a temporal resolution of 1 hour were carried out for annual and seasonal (summer/winter) maximum runoff derived from the long-term simulations.

Average annual runoff shows an increase of 0 to 10 % for the RCP2.6 ensemble and an increase of 0 to 20 % for the RCP8.5 ensemble at the end of the 21st century. Annual and winter average conditions (precipitation sums and average runoff) of the RCP8.5 ensemble show a robust increase across different ensemble simulations. Extreme events however show high variability and no conclusive and robust trend. Analysis shows a good relation between average values of precipitation and average runoff (MQ). Future development of simulated annual maximum runoffs shows only a weak relation with future simulated precipitation extremes. However, summer maximum runoffs tend to show a relation with summer precipitation extremes. The behaviour of winter runoffs might be explained by altered future conditions of snow aggregation and melt in combination with high soil moisture. With increasing average and extreme temperatures, snow fall, snow accumulation and concentrated runoff caused by snow melt in spring are less likely to occur.

One of the conclusions drawn is that especially for assessing extreme precipitation and its impacts on small hydrological catchments it is necessary to apply regional climate model projections with high spatial and temporal resolution where further improvement is expected by making use of the upcoming generation of climate simulations on convection permitting scale.

How to cite: Sauer, C., Fröhle, P., Nehlsen, E., Rechid, D., Bouwer, L., and Nam, C.: Analysing the bandwidths of hydrological change in small river catchments using an ensemble of high-resolution regional climate model projections, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8611, https://doi.org/10.5194/egusphere-egu21-8611, 2021.

Jens Kiesel et al.

Production of a large ensemble of climate simulations suitable for impact assessments is an attempt to enhance our knowledge about the associated uncertainties in future projections. However, the actual quantification of the change in the climate and its impact relies on the ensemble of models selected, particularly given the wide availability of climatic simulations from various initiatives, i.e. CMIP5, CORDEX.

Here, we hypothesize that historical streamflow observations contain valuable information to investigate practices for the selection of climate model ensembles. We apply eight selection methods (based on democracy, diversity of GCM, diversity of RCM, maximum information minimum redundancy, best performing hindcasted climate depiction, best performing hydrological model, simple climate model averaging and reliable ensemble average) to subset an ensemble available from 16 combinations of Euro-CORDEX GCM-RCM by comparing observed to simulated streamflow shift of the Danube from a reference period (1960–1989) to an evaluation period (1990–2014). Simulations are carried out with the well-performing Upper Danube COSERO hydrological model, spanning a calibration and evaluation period of more than 100 years. Comparison against no selection shows that an informed selection of ensemble members improves the quantification of climate change impacts where methods that maintain the diversity and information content of the full ensemble are favourable. In addition, the method followed allows the assessment which individual climate models perform best, where only three of 16 models were able to correctly reproduce the direction of streamflow change in each season.

Prior to carrying out climate impact assessments, we propose splitting the long-term historical data and using it to test climate model performance, sub-selection methods, and their agreement in reproducing the indicator of interest, which further provide the expectable benchmark of near- and far-future impact assessments. This test can further be applied in multi-basin experiments to obtain a better understanding of uncertainty propagation and uncertainty reduction in hydrological impact studies.

How to cite: Kiesel, J., Stanzel, P., Kling, H., Fohrer, N., Jähnig, S. C., and Pechlivanidis, I.: The more is not the merrier – an informed selection of climate model ensembles can enhance the quantification of hydrological change, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7108, https://doi.org/10.5194/egusphere-egu21-7108, 2021.

Mayank Suman and Rajib Maity

Indian Summer Monsoon is vulnerable to climate change. Analysis of precipitation over India suggests more increase in extreme precipitation over south India as compared to north and central India during post-1970 (1971-2017) as compared to pre-1970 (1930-1970) (Suman and Maity, 2020). This contrast in the characteristics of extreme precipitation over south and north India is expected to continue as revealed by the analysis of precipitation from the Coordinated Regional Downscaling Experiment (CORDEX) simulations. Additionally, precipitation extreme are expected to shift southward over South Asia in the future (2006-2100 as compared to 1961-2005). For instance, the Arabian Sea, south India, Myanmar, Thailand, and Malaysia are expected to have the maximum increase (~18.5 mm/day for RCP8.5 scenario) in mean extreme precipitation (average precipitation for the days with more than 99th percentile of daily precipitation). However, north and central India and Tibetan Plateau show relatively less increase (~2.7 mm/day for RCP8.5 scenario). The increase in extreme precipitation over most part of South Asia can be attributed to stronger monsoon due to increase in air temperature over Tibetan Platue and Himalayas, stronger positive Indian Ocean Dipole events, and high precipitatible water over land areas in the future. However, while analysis of moisture flux and moisture convergence at 850mb, an intense eastward shift is noticed for moisture flux (over Indian Ocean region). This shift in moisture flux along with associated changes in moisture convergence over landmass are found to intensify during days with extreme precipitation. These changes are expected to intensify the observed contrast in extreme precipitation over south and north India and shift the extreme precipitation southward over south Asia, causing more extreme precipitation events in the countries like Myanmar, Thailand, Malaysia, etc.

Keywords: Extreme Precipitation; Indian Summer Monsoon; Climate Change; Indian Ocean Dipole.



Suman, M., Maity, R. (2020), Southward shift of precipitation extremes over south Asia: Evidences from CORDEX data. Sci Rep 10, 6452 (2020). https://doi.org/10.1038/s41598-020-63571-x.

How to cite: Suman, M. and Maity, R.: Future Changes in extreme precipitation over South Asia and its causes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1736, https://doi.org/10.5194/egusphere-egu21-1736, 2021.

Valeriy Osypov et al.

A river basin management plan has to consider climate change impact because global warming influences the water cycle explicitly. For Ukraine, only continental-scale studies or(and) global hydrological models reflect the climate change impact on water resources. Such resolution is insufficient to develop confident adaptation strategies.

This study aims to assess changes in the river runoff, water flow formation, and soil water of the Desna river basin under future climate. The Desna supply Kyiv, Ukraine’s capital, with fresh water. Moreover, soil water capacity across the basin is critical for crop production, the leading sector of the region.

The framework consists of the process-based ecohydrological SWAT (Soil and Water Assessment Tool) model and eight high-resolution (~12 km) regional climate models from the EURO-CORDEX project forced by RCP4.5 and RCP8.5 scenarios till the end of the XXI century. The SWAT model was successfully calibrated on water discharge from 12 gauges across the basin, then it was driven by each climate model to achieve a range of possible future scenarios. This approach better represents the hydrological processes and achieves more confident results than in previous studies.

Seven of eight models project warmer and wetter climate in the near future (2021-2050), and all models project the same in the far future (2071-2100). According to the ensemble mean, the air temperature will increase by 1.1°C under RCP4.5 and 1.2°C under RCP8.5 in the near future, and by 2.2°C under RCP4.5 and 4.2°C under RCP8.5 in the far future. Precipitation surplus will reach 5% (range from -6% to 16%) under RCP4.5 and RCP8.5 in the near future, and 8% (from 2% to 17%) under RCP4.5 and 14% (from 3% to 23%) under RCP8.5 in the far future. The discharge will likely increase (mean signal 6-8% in the near future and 10-14% in the far future) mostly due to higher groundwater inflow.

Intra-annual changes could be very unfavorable for plant growth because of lower soil water content and higher temperature stress during the vegetation period. The models agree about precipitation surplus during the cold period but, in summer, all directions of change are almost equally possible.

We consider that, among other vulnerabilities of the Desna basin, the water stress for crops will be the main issue because of the high dependence of the economy on crop production. Attention should also be paid to forest fires, eutrophication, and the concentration of organic substances in the stream

How to cite: Osypov, V., Osadcha, N., Osadchyi, V., and Speka, O.: Climate change impact on water resources of the Desna river basin, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6327, https://doi.org/10.5194/egusphere-egu21-6327, 2021.

Jing Zhao

The elevated atmospheric carbon dioxide concentration (CO2), as a key variable linking human activities and climate change, seriously affects the watershed hydrological processes. However, whether and how atmospheric CO2 influences the watershed water-energy balance dynamics at multiple time scales have not been revealed. Based on long-term hydrometeorological data, the variation of non-stationary parameter n series in the Choudhury's equation in the mainstream of the Wei River Basin (WRB), the Jing River Basin (JRB) and Beiluo River Basin (BLRB), three typical Loess Plateau regions in China, was examined. Subsequently, the Empirical Mode Decomposition method was applied to explore the impact of CO2 on watershed water-energy balance dynamics at multiple time scales. Results indicate that (1) in the context of warming and drying condition, annual n series in the WRB displays a significantly increasing trend, while that in the JRB and BLRB presents non-significantly decreasing trends; (2) the non-stationary n series was divided into 3-, 7-, 18-, exceeding 18-year time scale oscillations and a trend residual. In the WRB and BLRB, the overall variation of n was dominated by the residual, whereas in the JRB it was dominated by the 7-year time scale oscillation; (3) the relationship between COconcentration and n series was significant in the WRB except for 3-year time scale. In the JRB, COconcentration and n series were significantly correlated on the 7- and exceeding 7-year time scales, while in the BLRB, such a significant relationship existed only on the 18- and exceeding 18-year time scales. (4) CO2-driven temperature rise and vegetation greening elevated the aridity index and evaporation ratio, thus impacting watershed water-energy balance dynamics. This study provided a deeper explanation for the possible impact of CO2 concentration on the watershed hydrological processes.

How to cite: Zhao, J.: Time-scale dependent mechanism of atmospheric CO2 concentration drivers of watershed water-energy balance, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8128, https://doi.org/10.5194/egusphere-egu21-8128, 2021.

Alexander Ivanov and Maria Kireeva

In the past two decades we see many signs of changing behaviour in hydrological regimes of Russian Plain rivers. River regimes classification was done in the early 1990s and it's possible that some rivers (especially in Don and Oka river basins) have already changed their behaviour. We believe that's the first time this was done by objective analysis and without reliance on experts opinion.

In this work we make an attempt at automatic and objective classification of water regime types for 220 rivers of Russian Plain and propose a method for automatic assesment of changes in hydrological behaviour of local rivers. We use monthly data and k-means clustering algorithm to classify each river water regime for every year with available data. Unlike most of other approaches we do not divide data by year but create clusters from all datapoints simultaniously. This allows us to use more datapoints and establish a more robust result. Next, when we have annual clusters for every datapoint we can assess the stability of water regime for each catchment over several decades and identify catchments with unstable and changing behaviour. 

By using this method we're able to automatically identify 5 distinct water regimes for the rivers of Russian Plain: three with dominant peaks caused by spring freshets in March, April and Februaty with most discharge happening over the course of a single month and two types of water regimes with maximal discharges in April and June, but lacking a pronounced peak in these months. Unlike previous calssifications we can identify the closest water regime for every year and therefore make an attempt at quantifying stability of these regimes and changes over time. By using a very naive approach and calculating a standard deviation over a moving window of 10 years it's possible to detect unstable regions and therefore select periods of stability and shifts for each subregion of Russian Plain.

We're able to identify Don and Oka basins as regions with the most changes in water regimes and it corresponds with research data. In addition rivers in Kola peninsula and Ural regions peninsula demonstrate a slight shift in stability. In terms of hydrological behaviour we see siginificant changes in Don and Oka river basins that shifted from spring freshet peak in April into water regime type with a peak in March or a more southern water regime with less pronounced April peak having precedenig winter thaws.

We believe that this simple approach at identifying water regimes and changes in them can be successfuly used for other regions than Russian Plane.

The study was supported by the Russian Science Foundation (grant No.19-77-10032) in methods and Russian Foundation for Basic Research (grant No.18-05-60021) for analyses in Arctic region 

How to cite: Ivanov, A. and Kireeva, M.: Identifying changes in hydrological behaviour of Russian Plain rivers over the last 70 years by using clustering analysis, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8327, https://doi.org/10.5194/egusphere-egu21-8327, 2021.

Gerrit H. de Rooij and Thomas Mueller

Occasionally, there is an interest in groundwater flows over many millennia. The input parameter requirement of numerical groundwater flow models and their calculation times limit their usefulness for such studies.

Analytical models require considerable simplifications of the properties and geometry of aquifers and of the forcings. On the other hand, they do not appear to have an inherent limitation on the duration of the simulated period. The simplest models have explicit solutions, meaning that the hydraulic head at a given time and location can be calculated directly, without the need to incrementally iterate through the entire preceding time period like their numerical counterparts.

We developed an analytical solution for a simple aquifer geometry: a strip aquifer between a no flow boundary and a body of surface water with a prescribed water level. This simplicity permitted flexible forcings: The non-uniform initial hydraulic head in the aquifer is arbitrary and the surface water level can vary arbitrarily with time. Aquifer recharge must be uniform in space but can also vary arbitrarily with time.

We also developed a modification that verifies after prescribed and constant time intervals if the hydraulic head is such that the land surface is covered with water. This excess water then infiltrates in areas where the groundwater level is below the surface and the remainder is discharged into the surface water. The hydraulic head across the aquifer is modified accordingly and used as the initial condition for the next time interval. This modification models the development of a river network during dry periods. The increased flexibility of the model comes at the price of the need to go through the entire simulation period one time step at a time. For very long time records, these intervals will typically be one year.

Given the uncertainty of the aquifer parameters and the forcings, the models are expected to be used in a stochastic framework. We are therefore working on a shell that accepts multiple values for each parameter as well as multiple scenarios of surface water levels and groundwater recharge rates, along with an estimate of their probabilities. The shell will generate all possible resulting combinations, the number of which can easily exceed 10000, then runs the model for each combination, and computes statistics of the average hydraulic head and the aquifer discharge into the surface water at user-specified times.

A case study will tell if this endeavor is viable. We will model the aquifer below the mountain range north of Salalah in Oman, which separates the desert of the Arabian Peninsula from the coastal plain at its southern shore. Rainfall estimates from the isotopic composition of stalactites in the area indicate distinct dry and wet periods in the past 300 000 years. In combination with estimated sea level fluctuations over that period, this provides an interesting combination of forcings. We examine the dynamics of the total amount of water stored in the aquifer, and of the outflow of water from the aquifer into the coastal plain.

How to cite: de Rooij, G. H. and Mueller, T.: Groundwater modelling for time periods of up to 105 years, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7948, https://doi.org/10.5194/egusphere-egu21-7948, 2021.

Hanieh Seyedhashemi et al.

Air temperature has been increasing all around the world over the past decades. Owing to its sensitivity to air temperature, it is consequently expected that stream temperature experiences an increase as well. However, due to paucity of long-term stream temperature data, assessments of the magnitude of such trends in relation with landscape and hydrological changes have remained scarce.

The present study used a physically-based thermal model (T-NET: Temperature-NETwork), coupled with a semi-distributed hydrological model (EROS) to reconstruct past daily stream temperatures and discharges at the scale of the Loire River basin in France (105 km2 with 52278 reaches). The ability of both models to reconstruct long-term trends was assessed at 44 gauging stations and 11 stream temperature stations.  

T-NET simulations over the 1963-2017 period show that there has been a significant increasing trend in stream temperatures for at least 70% of reaches in all seasons (median=0.36 °C/decade). Significantly increasing trends are more prominent in spring (Mar-May) and summer (Jun-Aug) with a median increase of 0.37 °C (0.11 to 0.8°C) and 0.42°C (0.14 to 1 °C) per decade, respectively. For 81 % of reaches, annual stream temperature trends are greater than annual air temperature trends (median ratio=1.21; interquartile ranges: 1.06-1.44). Greater increases in stream temperature in spring and summer are found in the south of the basin, mostly in the Massif Central (up to 1°C/decade) where greater increase in air temperature (up to 0.67 °C/decade) and greater decrease in discharge (up to -16%/decade) occur jointly. The increase of stream temperature is also higher in large rivers compared to small rivers where riparian vegetation shading mitigate the increase in temperature. For the majority of reaches, changes in stream temperature, air temperature, and discharge significantly intensified in the late 1980s.

These climate-induced changes in the annual and seasonal stream temperature could help us to explain shifts in the phenology and geographical distribution of cold-water fish especially in the south of the basin where trends are more pronounced.

How to cite: Seyedhashemi, H., Moatar, F., Vidal, J.-P., Thiery, D., Monteil, C., and Hendrickx, F.: Trend of stream temperature and its drivers over the past 55 years in a large European River basin, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9529, https://doi.org/10.5194/egusphere-egu21-9529, 2021.

Thibault Lemaitre-Basset et al.

Climate change might cause regional modifications of precipitation regimes and increase of air temperature and evaporative demand. As a consequence, the potential increase in evapotranspiration has been determined as a key risk, which could lead to a decrease in runoff and water resources. In many hydrological models, evapotranspiration is determined by a preliminary computation of the evaporative demand, potential evapotranspiration (PET). Estimating PET for future climate is still subject to extensive research, due to the multiplicity of PET formulations and the uncertainties associated with the climatic variables used within these formulations. Physically-based PET formulations use several climatic variables whose simulations come with large uncertainties, while more simple empirical PET formulations rely on limited climatic variables. However, their empiric development questions their robustness for transient climatic conditions.

In this work, we examined the evolution of PET under future climate conditions. We also investigated to what extent seven different classical PET formulations could modify the partitioning of uncertainty associated with climate projections.

The importance of PET formulation on the total uncertainty of the potential evapotranspiration changes was evaluated within a multiscenario multimodel ensemble (Euro-CORDEX climate projections from CMIP5 experiment) over the whole France. This approach was used to account for the uncertainty on the unknown future greenhouse gas emissions trajectories, and differences coming from climate models (GCMs and RCMs). An analysis of the variance (ANOVA), allowed us to determine the contribution of each modelling step to the total uncertainty of PET estimates over entire France. The ANOVA was applied on an ensemble completed by a Bayesian process, to have a balance set of projections to analyze.

The results showed that the relative importance of PET formulations was found to be minor compared with other uncertainty sources (GCMs and RCMs) in the future. We also found that divergences of PET among the different formulations were highly dependent on the temperature anomaly. Based on our experimental design, we concluded that the choice of PET formulation might not constitute a major element of uncertainty reduction for hydrological projections.

How to cite: Lemaitre-Basset, T., Oudin, L., Thirel, G., and Collet, L.: Uncertainty on evapotranspiration formulation and its hydrological implication under climate change over France, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9946, https://doi.org/10.5194/egusphere-egu21-9946, 2021.

Artemis Roodari and Markus Hrachowitz

The transboundary Helmand River basin is the main drainage system for large parts of Afghanistan and the Sistan region of Iran. Due to the reliance of this arid region on water from the Helmand River, a better understanding of hydrological drought pattern and the underlying drivers in the region are critically required for an effective management of the available water. The objective of this paper is therefore to analyse and quantify spatio-temporal pattern of drought and the underlying processes in the study region. More specifically we test for the Helmand River Basin the following hypotheses for the 1970-2006 period: (1) drought characteristics, including frequency and severity systematically changed over the study period, (2) the spatial pattern and processes of drought propagation through the Helmand River Basin also changed and (3) the relative roles of climate variability and human influence on changes in hydrological droughts can be quantified. It was found that drought characteristics varied throughout the study period, but did largely show no systematic trends. The same was observed for the time series of drought indices SPI and SPEI, which exhibited considerable spatial coherence and synchronicity throughout the basin indicating that, overall, droughts similarly affect the entire HRB with little regional or local differences. In contrast, analysis of SDI exhibited significant negative trends in the lower parts of the basin, indicating an intensification of hydrological droughts. It could be shown that with a mean annual precipitation of ~250 mm y-1, streamflow deficits and thus hydrological drought throughout the HRB are largely controlled by precipitation deficits, whose annual anomalies on average account for ±50 mm y-1 or ~20% of the water balance of the HRB, while anomalies of total evaporative fluxes on average only account for ±20mm y-1. The two reservoirs in the HRB only played a minor role for the downstream propagation of streamflow deficits. Irrigation water abstraction had a similarly limited effect on the magnitude of streamflow deficits, accounting for ~10% of the water balance of the HRB. However, the downstream parts of the HRB moderated the further propagation of streamflow deficits and associated droughts in the early decades of the study period. This drought moderation function of the lower basin was gradually and systematically inverted by the end of the study period, when the lower basin eventually amplified the downstream propagation of flow deficits and droughts. This shift from drought moderation to drought amplification in the lower basin is likely a consequence of increased agricultural activity and the associated increases in irrigation water demand from ~13 mm y-1 at the beginning of the study period to ~23 mm y-1 at the end and thus in spite of being only a minor fraction of the water balance. Overall the results of this study illustrate that flow deficits and the associated droughts in the HRB clearly reflect the dynamic interplay between temporally varying regional differences in hydro-meteorological variables together with subtle and temporally varying effects linked to direct human intervention.

How to cite: Roodari, A. and Hrachowitz, M.: Signatures of human intervention – or not? Downstream intensification of hydrological drought along a large Central Asian River: the individual roles of climate variability and land use change, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-481, https://doi.org/10.5194/egusphere-egu21-481, 2021.

Julie Collignan et al.

In a context of climate change, the stakes surrounding water availability and use are getting higher, especially in semi-arid climates. Human activities such as irrigation and land cover changes impact the water cycle, raising questions around the effects it could have on regional atmospheric circulation and how to separate the impact of climate change from the impact of anthropogenic activities to better understand their role in the historical records. The ORCHIDEE Land Surface Model from Institut Pierre Simon Laplace (IPSL) simulates global carbon cycle and aims at quantifying terrestrial water and energy balance. It is being developed at regional scale but does not include satisfying hypothesis to account for human activities such as irrigation at such scale so far.

We propose a methodology to semi-empirically separate the effect of climate from the impact of the changing catchment characteristics on river discharge. It is based on the Budyko framework and allows to characterise the annual river discharge of over 363 river monitoring stations in Spain. The Budyko parameter is estimated for each basin and represents its hydrological characteristics. Precipitations and potential evapotranspiration are derived from the forcing dataset GSWP3 (Global Soil Wetness Project Phase 3) – from 1901 to 2010 –. Two methods are used to estimate evapotranspiration : the first uses evapotranspiration from the ORCHIDEE LSM outputs while the second deduced evapotranspiration from river discharge observations and the water balance equation. The first method only accounts for the effects of atmospheric forcing while the other combines, through the observations, climatic and non-climatic processes over the watersheds. We then study the evolution over the Budyko parameter fitted with these two estimates of evaporation. Studying the watershed parameter allows us to free ourselves from some of the climate interannual variability compared to directly looking at changes in the river discharge and better separate anthropogenic changes from the effect of climatic forcing.

Our results show that for most basins tested over Spain, there is an increasing trend in the Budyko parameter representing increasing evaporation efficiency of the watershed which can not be explained by the climate forcing. This trend is consistent with changes in irrigation equipment and land cover changes over the studied period. However changes of the basin characteristics can not be fully quantified by this variables. Other factors as glaciers melting which derails the water balance over our time of study.

The methodology needs to be extended to other areas such as Northern Europe to see if the differences in response of the catchments to anthropogenic changes quantified by our methodology corresponds to known contrasts. Balance between climatic and anthropogenic changes of basin characteristics are different in semi-arid climate than in northern more humid regions.

How to cite: Collignan, J., Polcher, J., and Quintana Seguí, P.: Identifying and quantifying the impact of non-climatic effects on the water cycle in a semi-arid environment , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7302, https://doi.org/10.5194/egusphere-egu21-7302, 2021.

Sandra Pool et al.

Irrigated agriculture is the major water consumer in the Mediterranean region. Improved irrigation techniques have been widely promoted to reduce water withdrawals and increase resilience to climate change impacts. In this study, we assess the impact of the ongoing transition from flood to drip irrigation on future hydroclimatic regimes in the agricultural areas of Valencia (Spain). The impact assessment is conducted for a control period (1971-2000), a near-term future (2020-2049) and a mid-term future (2045-2074) using a chain of models that includes five GCM-RCM combinations, two emission scenarios (RCP 4.5 and RCP 8.5), two irrigation scenarios (flood and drip irrigation), and twelve parameterizations of the hydrological model Tetis. Results of this modelling chain suggest considerable uncertainties regarding the magnitude and sign of future hydroclimatic changes. Yet, climate change could lead to a statistically significant decrease in future groundwater recharge of up -6.6% in flood irrigation and -9.3% in drip irrigation. Projected changes in actual evapotranspiration are as well statistically significant, but in the order of +1% in flood irrigation and -2.1% in drip irrigation under the assumption of business as usual irrigation schedules. The projected changes and the related uncertainties will pose a challenging context for future water management. However, our findings further indicate that the effect of the choice of irrigation technique may have a greater impact on hydroclimate than climate change alone. Explicitly considering irrigation techniques in climate change impact assessment might therefore be a way towards better informed decision-making.

This study has been supported by the IRRIWAM research project funded by the Coop Research Program of the ETH Zurich World Food System Center and the ETH Zurich Foundation, and by the ADAPTAMED (RTI2018-101483-B-I00) and TETISCHANGE (RTI2018-093717-B-I00) research projects funded by the Ministerio de Economia y Competitividad (MINECO) of Spain including EU FEDER funds.

How to cite: Pool, S., Francés, F., Garcia-Prats, A., Pulido-Velazquez, M., Sanichs-Ibor, C., Schirmer, M., Yang, H., and Jiménez-Martínez, J.: Relative impact of irrigation techniques and climate change on hydroclimatic regimes in the Mediterranean region, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2242, https://doi.org/10.5194/egusphere-egu21-2242, 2021.

Mokrane Kadir and Marnik Vanclooster

The water resources of Mediterranean countries are strongly affected by climate change and anthropogenic activities, which exert considerable pressure on the overall water security.  Understanding the relative contributions of each of the possible causal factors to the hydrological alteration is pivotal to design sustainable water resources management strategies. In this study, the hydrological alteration of the Isser catchment in Algeria is assessed and explained in terms of possible explanatory factors. A long term hydro-meteorological dataset was reconstructed and the nonparametric Mann-Kendall test was used to detect the alteration of streamflow and the possible causal factors. To identify the role of causal factors in the hydrologic alterations, two techniques were used.  First, Convergent Cross Mapping (CCM), which is an advanced data-based nonlinear time-series analysis tool, was used to identify causality in time-series. Second, a Fuzzy Analytical Hierarchical Process (FAHP) expert-based model was applied to assess the possible underlying causes for hydrologic alterations and to quantify the potential influences of human activities and climate change. The results of the trend analysis show a significant downward trend for streamflow (pvalue< 0.05) for the period 1971-2010. The CCM method shows that the streamflow alteration is unidirectionally caused by changes in precipitation, temperature, irrigation, evapotranspiration, and NDVI patterns and that there is little feedback from streamflow alteration to these causing factors.  The FAHP suggests that climate change is dominating the decreasing trend in streamflow, being responsible for 60 % of the alterations as compared to 40 % of the alterations caused by changes in the land use patterns and intensive water extraction.

How to cite: Kadir, M. and Vanclooster, M.: Exploring causes of hydrological alterations and the relative contributions of climate change and human activities in the Isser catchment, Algeria, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16500, https://doi.org/10.5194/egusphere-egu21-16500, 2021.

Shasha Han and Louise Slater

Changes in precipitation and land cover are important drivers of change in catchment streamflow, yet quantifying their influence remains a major challenge. This work aims to understand how streamflow may evolve under different scenarios of future precipitation and urbanization across the UK. A collection of catchments from the National River Flow Archive (NRFA) that have experienced significant changes in flows and urbanization were selected. Both historical observations and future projections of precipitation and urban land cover were extracted within each study catchment, for different emissions and socio-economic scenarios including Representative Concentration Pathways (RCPs) and Shared Socio-Economic Pathways (SSPs). Distributional regression models – Generalised Additive Models for Location Scale and Shape (GAMLSS) – were developed using historical precipitation, land cover, and streamflow, and employed to project future streamflow using bias-corrected projections of precipitation and land cover. The results improve our understanding of streamflow response to climate and land cover changes and provide further insights for water resources management and land use development.

How to cite: Han, S. and Slater, L.: Projecting future streamflow under changing climate and urban land cover across the UK, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3084, https://doi.org/10.5194/egusphere-egu21-3084, 2021.

Shilei Peng et al.

Hydrological processes at basin scale are driven by climate and land-use changes. Hiso River watershed (HRW) is within a radiocesium contaminated area caused by the disaster in Fukushima Daiichi nuclear power plant (FDNPP). It’s urgently needed to make evaluations on how changes of climate and land-use bring impacts on hydrological processes, which control pollutants transport in watershed. This study applied a combination method of Statistical DownScaling Model (SDSM) and Soil and Water Assessment Tool (SWAT) to generate future climatic and hydrologic variables. Future climate data was obtained from three Representative Concentration Pathway (RCP2.6, 4.5 and 8.5) scenarios of a single General Circulation Models (GCMs) in three future periods of 2030s, 2060s and 2090s (2010-2039, 2040-2069, 2070-2099), with a baseline period (1980-2009). Furthermore, according to land-use change in HRW during 2013-2017, three land-use change scenarios under the three future climate scenarios were established. Results suggested that SDSM showed good capabilities in capturing daily maximum/minimum temperature and precipitation. The SWAT model presented good performances in simulating monthly and yearly streamflow. Results also suggested projected higher temperatures and lower rainfall led to decreased annual water yield and evapotranspiration (ET). The annual water yield and ET decreased in most seasons while had a slight increase in spring. RCP8.5 scenario always generated larger magnitudes for climatic variables and water balance components compared with other climate scenarios. Land-use changes had strong impact on surface runoff and groundwater flow. These findings could provide reference for decontamination and revitalization policy-making under complicated land use and climate change conditions.

How to cite: Peng, S., Wang, C., Eguchi, S., Kuramochi, K., Igura, M., Kohyama, K., Ohkoshi, S., and Hatano, R.: Response of hydrological processes to climate and land use changes in Hiso River watershed, Fukushima, Japan, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5316, https://doi.org/10.5194/egusphere-egu21-5316, 2021.

Dario Ruggiu et al.

The assessment of climate change and land use modifications effects on hydrological cycle is challenging. We propose an approach based on Budyko theory to investigate the relative importance of natural and anthropogenic drivers on water resources availability. As an example of application, the proposed approach is implemented in the island of Sardinia (Italy), which is affected by important processes of both climate and land use modifications. In details, the proposed methodology assumes the Fu’s equation to describe the mechanisms of water partitioning at regional scale and uses the probability distributions of annual runoff (Q) in a closed form. The latter is parametrized by considering simple long-term climatic info (namely first orders statistics of annual rainfall and potential evapotranspiration) and land use properties of basins.

In order to investigate the possible near future water availability of Sardinia, several climate and land use scenarios have been considered, referring to 2006-2050 and 2051-2100 periods. Climate scenarios have been generated considering fourteen bias corrected outputs of climatic models from EUROCORDEX’s project (RCP 8.5), while three land use scenarios have been created following the last century tendencies.

Results show that the distribution of annual runoff in Sardinia could be significantly affected by both climate and land use change. The near future distribution of Q generally displayed a decrease in mean and variance compared to the baseline.   

The reduction of  Q is more critical moving from 2006-2050 to 2051-2100 period, according with climatic trends, namely due to the reduction of annual rainfall and the increase of potential evapotranspiration. The effect of LU change on Q distribution is weaker than the climatic one, but not negligible.

How to cite: Ruggiu, D., Urru, S., Deidda, R., and Viola, F.: Climate and land use change impacts on water resources in Sardinia (Italy), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10894, https://doi.org/10.5194/egusphere-egu21-10894, 2021.

Qing He et al.

Disentangling the effects of climate and land use changes on regional hydrological conditions is critical for local water and food security. The water variability over climate transition regions at the midlatitudes is sensitive to changes in regional climate and land use. Gansu, located in northwest China, is a midlatitude climate transition region with sharp climate and vegetation gradients. In this study, the effects of climate and land‑use changes on water balances are investigated over Gansu between 1981 and 2015 using a Budyko framework. Results show that there is reduced runoff generation potential over Gansu during 1981 and 2015, especially in the southern part of the region. Based on statistical scaling relationships, local runoff generation potential over Gansu are related to the El Nino-Southern Oscillation (ENSO). Intensified El Nino conditions weaken the Asian monsoons, leading to precipitation deficits over Gansu. Moreover, the regional evapotranspiration (ET) is increasing due to the warming temperature. The decreasing precipitation and increasing ET cause the decline of runoff generation potential over Gansu. Using the dynamical downscaling model outputs, the Budyko analysis indicates that increasing coverage of forests and croplands may lead to higher ET and may reduce runoff generation potential over Gansu. Moreover, the contributions of climate variability and land‑use changes vary spatially. In the southwest part of Gansu, the impacts of climate variability on water variations are larger (around 80%) than that of land‑use changes (around 20%), while land use changes are the dominant drivers of water variability in the southeast part of the region. The decline of runoff generation potential reveals a potential risk for local water and food security over Gansu. The water‑resource assessment approach developed in this study is applicable for collaborative planning at other climate transition regions at the midlatitudes with complex climate and land types for the Belt and Road Initiative.

How to cite: He, Q., Chun, K. P., Yetemen, O., Dieppois, B., Chen, L., and Pan, X.: Impacts of climate and land use changes on water variability, using a Budyko framework: case study in Gansu, China, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10613, https://doi.org/10.5194/egusphere-egu21-10613, 2021.

Daeha Kim and Jong Ahn Chun

While the Budyko framework has been a simple and convenient tool to assess runoff (Q) responses to climatic and surface changes, it has been unclear how parameters of a Budyko function represent the vertical land-atmosphere interactions. Here, we explicitly derived a two-parameter equation by correcting a boundary condition of the Budyko hypothesis. The correction enabled for the Budyko function to reflect the evaporative demand (Ep) that actively responds to soil moisture deficiency. The derived two-parameter function suggests that four physical variables control surface runoff; namely, precipitation (P), potential evaporation (Ep), wet-environment evaporation (Ew), and the catchment properties (n). We linked the derived Budyko function to a definitive complementary evaporation principle, and assessed the relative elasticities of Q to climatic and land surface changes. Results showed that P is the primary control of runoff changes in most of river basins across the world, but its importance declined with climatological aridity. In arid river basins, the catchment properties play a major role in changing runoff, while changes in Ep and Ew seem to exert minor influences on Q changes. It was also found that the two-parameter Budyko function can capture unusual negative correlation between the mean annual Q and Ep. This work suggests that at least two parameters are required for a Budyko function to properly describe the vertical interactions between the land and the atmosphere.

How to cite: Kim, D. and Chun, J. A.: Two parameters are required for a Budyko function to describe the land-atmosphere interaction, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3554, https://doi.org/10.5194/egusphere-egu21-3554, 2021.

Sushree Swagatika Swain et al.

Inherent knowledge of the river basin-scale water balance components is essential for long‐term management of water resources planning and food security at a regional scale. This study explains a combined approach using the Soil and Water Assessment Tool (SWAT) followed by the Sequential Uncertainty Fitting program (SUFI‐2) concept to calibrate and validate the hydrologic models of the Brahmani basin based on observed streamflow at a monthly time‐step. The water balance components in terms of blue water flow (surface runoff, return flow, and lateral flow), green water flow (actual evapotranspiration), and green water storage (soil moisture storage) of the study area are assessed at a decadal scale (1979-88, 1989-98, and 1999-2008). The first 7 years of each decade are considered as calibration period (1979-85, 1989-95, and 1999-05) and the remaining years are the validation period (1986-88, 1996-98, and 2006-08). The results of the initial decade (1979-88) showed that there is a balance between blue water flow, green water flow, and green water storage components. There is an increasing trend in blue water flow and green water flow components in the mid-decade (1989-98). However, there is a fluctuation in green water storage. It is decreasing in mid-decade and increasing towards the end decade (1999-2008). The warm and humid climate of the study area is expected to affect the variation of the above components. The vulnerability of water balance components is crucial for maintaining regional-scale water demand and food security. However, the alarming impacts of climate change could adversely affect the above situation. Water availability component analysis at a decadal scale has not been explored widely in the present study area. This study can help the policy-makers to maintain a balance between water demand from different sectors and availability to avoid water scarcity of a river basin in the future. Further, the developed approach for the analysis of blue and green water can be applied in other arid and semi‐arid regions.

How to cite: Swain, S. S., Mishra, A., Chatterjee, C., and Sahoo, B.: Decadal-scale assessment of blue and green water resources in the Brahmani river basin, Odisha, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10243, https://doi.org/10.5194/egusphere-egu21-10243, 2021.

Deniz Bozkurt et al.

Atmospheric rivers (ARs) are important components of the global water cycle as they are responsible for over 90% of the poleward moisture transport at middle to high latitudes. ARs travelling thousands of kilometers over arid North Africa could interact with the highlands of the Mesopotamia and thus affect the hydrometeorology and water resources of the Euphrates-Tigris Basin. Here, we use a state-of-the-art AR tracking database, and reanalysis and observational datasets to investigate the climatology (1979-2017) and influences of these ARs in snowmelt season (March-April). The Red Sea and northeast Africa are found to be the major source regions of these ARs, which are typically associated with the eastern Mediterranean trough positioned over the Balkan Peninsula and a blocking anticyclone over the Near East-Caspian region, triggering southwesterly air flow towards the highlands of the Euphrates-Tigris Basin. AR days exhibit enhanced precipitation over the crescent-shaped orography of the Euphrates-Tigris Basin. Mean AR days indicate wetter (up to +2 mm day-1) and warmer (up to +1.5oC) conditions than all-day climatology. On AR days, while snowpack tends to decrease (up to 30%) in the Zagros Mountains, it can show decreases or increases in the Taurus Mountains depending largely on elevation. A further analysis with the aid of observations and reanalysis for the three extreme AR events indicates that ARs coinciding with large scale sensible heat transport can have notable impacts on the surface hydrometeorological conditions such as snowmelt, rain-on-snow precipitation and increasing daily discharges of the Euphrates and Tigris rivers. These results suggest that ARs can have notable impacts on the hydrometeorology and water resources of the basin, particularly of lowland Mesopotamia, a region that is famous with great floods in the ancient narratives.

How to cite: Bozkurt, D., Sen, O. L., Ezber, Y., Guan, B., Viale, M., and Caglar, F.: Impacts of atmospheric rivers on the hydrometeorology of the Euphrates-Tigris Basin in the snowmelt season, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3194, https://doi.org/10.5194/egusphere-egu21-3194, 2021.

Arnaud Cerbelaud et al.

Situated in the South-West Pacific, New Caledonia is a tropical island dominated by a central mountain range and is subject to cyclones, regular intense precipitation events and flash-flooding. Recent fine-scaled projections of climate change in New Caledonia show that the frequency and intensity of extreme precipitation events could be reduced by ~ 20% by 2080-2100 [Dutheil et al., 2020]. This paper investigates the ability of the WRF-Hydro/Noah-MP modelling framework to represent the hydrological regime of six watersheds in New Caledonia. A nearly 2-year long WRF ideal atmospheric forcing was completed with observed precipitations from 24 rain gauges using two rainfall spatial interpolation methods at 0.2 km-resolution. This study mainly seeks to calibrate the uncoupled WRF-Hydro/Noah-MP system as well as to evaluate its performance upon short and contrasted heavy rainfall events between 2012 and 2014. Particular attention was paid to (i) the sensitivity of calibration processes to rainfall spatial interpolation methods, (ii) the consistency in modelled soil moisture storage and (iii) the reliability of hydrograph separation provided by WRF-Hydro.

After automatic calibration relying upon the DDS algorithm [Tolson and Shoemaker, 2007], streamflow simulations show overall good performance with Nash–Sutcliffe efficiencies (NSE) greater than 0.6 on a 21-month period for all watersheds. Standard hydrological features of all studied watersheds are well reproduced. The quality of simulation is found to be decreasing with lower values of runoff coefficient. We show on three watersheds that spatial distribution of rainfall can highly condition the calibration process and thus greatly modify modelled soil moisture storage and in result the shape of simulated flash floods. WRF-Hydro’s hydrograph decomposition between surface and underground runoff is presented and compared with known characteristics of watersheds as well as with other quickflow/baseflow separation methods. To our knowledge, this work is the first attempt to use the uncoupled WRF-Hydro hydro-meteorological model for flash flood analysis in New Caledonia and opens a pathway to study multiple hydrological and climatic features in the region in the context of climate change.

Keywords: hydro-meteorological modelling, WRF-Hydro, Noah-MP, flash flood, rainfall spatial interpolation, hydrograph separation, baseflow, New-Caledonia

How to cite: Cerbelaud, A., Lefèvre, J., Genthon, P., and Menkes, C.: Assessment of the WRF-Hydro uncoupled hydro-meteorological model on flashy watersheds of the tropical island of New Caledonia (South-West Pacific), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-344, https://doi.org/10.5194/egusphere-egu21-344, 2020.

Lasyamayee L Sahoo and Subashisa Dutta

The sparsely distributed meteorological centers fails to provide enough information regarding spatial patterns. Even at places where dense meteorological stations are available, it is difficult to develop realistic gridded data due to the complex topography and climatic variability. Some of the climate as well as hydrological model require spatially continuous datasets as inputs. It is possible to obtain a continuous surface of raster datasets with the help of interpolation methods where each value is assigned based on surrounding values using specific mathematical formulas. For present study, various interpolation methods, like Inverse distance weighted, ordinary krigging, thin plate smoothing spline; has been compared for maximum and minimum temperature. Error in the interpolated data was analyzed by independent cross validation method, in which measurements like root mean square error (RMSE), mean squared relative error (MSRE), coefficient of determination (r2) and coefficient of efficiency (CE) were adopted for performance evaluation. Method with minimum error was chosen for developing the final map. It provides an effective way for mapping the meteorological variables in a topographically diverse region. In this case, an Indian state Odisha is chosen as study area. The state consists of 10 different agro-climatic zones and sees several weather systems across the year. The area suffers with floods, drought, heat waves and costal erosion almost every year with variable intensity. Strong heat waves in summer affect the human health, agriculture, construction efficiency and labour productivity. As three-fourth of the state is filled with mountains and high lands, monitoring network is sparsely distributed. Despite small latitudinal difference, temperature changes considerably with respect to both space and time. Here interpolation method plays a vital role to avoid uncertainty in modelling. Based on the generated maps, vulnerable areas on the basis of maximum temperature in summer and minimum temperature in winter is identified. Several indicators and vulnerability indices has been used.

How to cite: Sahoo, L. L. and Dutta, S.: Comparison of Spatial Interpolation Methods for Mapping Daily Air Temperature , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13970, https://doi.org/10.5194/egusphere-egu21-13970, 2021.

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