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HS2.4.1

EDI
Understanding the links between hydrological variability and internal/natural climate variability

In the current context of global change, assessing the impact of climate variability and changes on hydrological systems and water resources is increasingly crucial for society to better-adapt to future shifts in water resources, as well as extreme conditions (floods and droughts). However, important sources of uncertainty have often been neglected in projecting climate impacts on hydrological systems, especially uncertainties associated with internal/natural climate variability, whose contribution to near-future changes could be as important as forced anthropogenic climate changes at the regional scales. Internal climate modes of variability (e.g. ENSO, NAO, AMO) and their impact on the continent are not always properly reproduced in the current global climate models, leading to large underestimations of decadal climate and hydro-climatic variability at the global scale. At the same time, hydrological response strongly depends on catchment properties, whose interactions with climate variability are little understood at the decadal timescales. These factors altogether significantly reduce our ability to understand long-term hydrological variability and to improve projections and reconstructions of future and past hydrological changes upon which improvement of adaption scenarios depends.

We welcome abstracts capturing recent insights for understanding past or future impacts of large-scale climate variability on hydrological systems and water resources as well as newly developed projection and reconstruction scenarios. Results from model intercomparison studies are encouraged.

Co-organized by CL2
Convener: Bastien DieppoisECSECS | Co-conveners: Hayley Fowler, Klaus HaslingerECSECS, Jean-Philippe Vidal
Presentations
| Wed, 25 May, 08:30–11:50 (CEST)
 
Room L2

Wed, 25 May, 08:30–10:00

Chairpersons: Bastien Dieppois, Klaus Haslinger, Jean-Philippe Vidal

08:30–08:37
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EGU22-589
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ECS
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marc auriol amalaman et al.

Summary: The decline in rainfall experienced by the West African band in the decades 70 and 80 strongly affected the flow in the various sub-catchments. In order to better identify the different modes of variability, this work is dedicated to studying the relationship between the temperature of the Atlantic Ocean and changes in flow in the N'zi watershed. Continuous wavelet analysis was used for signal search signal in the Fêtêkro (1960-1997) and N'zianouan (1960-2010) hydrometric series. As for the consistency in wavelet, it made it possible to verify the link between the flow and Atlantic Ocean temperature indices (North Atlantic Temperature: TNA and South Atlantic Temperature: TSA). Continuous wavelet analysis shows a fairly marked variability overall in high frequencies (6 months to 1 year) and interannual (> 1 year). Thus, at the Fêtêkro station north of the basin, the annual scale (1 year) records half of the variability ready with an estimated signal at 46.09%.  For the N'zianouan station, 37.18% explains the variability of the signal. At this stage, the Fêtêkro station has a rather pronounced variability to the detriment of that of N'zianouan. At the level of low frequency variability, the N'zianouan station has a fairly pronounced variability from 1 to 7 years.  Periodicity (1 – 2; 2 – 4 years) marks the highest signal (19.78%). The station of Fêtêkro shows a signal in the decade 60 estimated at 9.46% at 2-year frequency. As for wavelet consistency, it indicates a strong influence of the TSA.  index. In Fêtêkro, a consistency in phase is perceptible from 2 years in the decades 60 and 70.  At the frequency (4-8 years), this logic is observed over the entire time series. At the station of N'zianouan, we observe this reality in the decades 60 and 80 at periodicity (2-6 years), and (7-9 years) from 1990. Therefore, the results of the coherence show that the TSA index strongly impacts the flow in the N'zi watershed.

Keywords: TSA, TNA, frequency, variability, N'zi watershed

 

How to cite: amalaman, M. A., Mahe, G., Tra Bi, A. Z., Diomande, B. I., Rouche, N., Nouaceur, Z., and Laignel, B.: STUDY OF THE RELATIONSHIP BETWEEN THE TEMPERATURE OF THE ATLANTIC OCEAN AND HYDROLOGICAL VARIABILITY IN THE N'ZI WATERSHED (Central-North Côte d'Ivoire), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-589, https://doi.org/10.5194/egusphere-egu22-589, 2022.

08:37–08:44
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EGU22-2859
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ECS
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On-site presentation
Lisa Baulon et al.

Groundwater level (GWL) variations can be expressed over a wide range of timescales. As aquifers act as low-pass filters, low-frequency variability (interannual to decadal variability) originating from large-scale climate variability represents a significant part of GWL variance. Anthropogenically-driven climate change may affect, and have maybe already affected, the internal climate variability which explains the low-frequency variability of hydrological processes. Such changes in internal climate variability could therefore affect GWL variations. How GWL, including extremes, may respond to such changes and variations in climate variability however remains an open question.

 

To tackle this issue, we implemented an empirical numerical approach allowing to assess the sensitivity of aquifers to changes in large-scale climate variability, using the whole Seine hydrosystem (76000 km2) as a case study. The approach consisted in: i) identifying and modifying the spectral content of precipitation, originating from large-scale climate variability, using signal processing; ii) injecting perturbed precipitation fields as input in a physically-based hydrological/hydrogeological model (the CaWaQS software) for the Seine river basin for simulating perturbed GWL; iii) comparing the spectral content, trend and extremes of perturbed GWL with the reference GWL. We used the Safran precipitation field over the period 1970-2018, which was initially used for model calibration and validation. GWL data for the Seine basin is a subset of a database of climate-sensitive time series (i.e. low anthropogenic influence) recently set up at the BRGM and University of Rouen Normandy. First, the Safran reanalysis and observed GWL time series were analyzed using continuous wavelet transform to identify the different timescales of variability: interannual (2-4yr and 5-8yr) and decadal (~15yr). Then, the different timescale of precipitation time series were extracted using maximum overlap discrete wavelet transform. For each time series of the precipitation field, the amplitude of each timescale was modified individually, by either increasing or decreasing it by 50%. This led to six scenarios of perturbed low-frequency variability of precipitation, which are subsequently used as input in the CaWaQS model to assess the response of GWL variability and extremes.

 

Preliminary results indicate that perturbations of the amplitude of interannual to decadal precipitation variability result in substantial changes in the variability of GWL, affecting the same timescales, as well as timescales that were not modified in the precipitation field. Implications of these findings on potential trends and the frequency of extremes of GWL is currently being explored.

How to cite: Baulon, L., Fossa, M., Massei, N., Flipo, N., Gallois, N., Fournier, M., Dieppois, B., Boé, J., Danaila, L., Allier, D., and Bessiere, H.: Sensitivity of groundwater level in the Seine River basin to changes in interannual to decadal climate variability, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2859, https://doi.org/10.5194/egusphere-egu22-2859, 2022.

08:44–08:51
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EGU22-8209
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ECS
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Virtual presentation
Job Ekolu et al.

Sub-Saharan Africa is affected by a high-level of temporal and spatial climate variability, with large impacts on water resources, human lives and economies, notably through hydrological extremes, such as floods and droughts. Using a newly reconstructed 65-year daily streamflow dataset of over 600 stations distributed throughout sub-Saharan Africa, we first highlight that the frequency, intensity and duration of hydrological extremes are strongly impacted by decadal to multi-decadal variations. However, the key factors driving such decadal to multi-decadal variability remain poorly documented and understood. To address this research gap, we first compile information on local-scale (precipitation, temperature, soil moisture) and large-scale (e.g., El Niño–Southern Oscillation, Atlantic Multidecadal Variability) drivers. Then, by using relative importance analysis and multiple datasets, we investigate the contribution of large-scale versus regional-scale processes in driving decadal to multi-decadal variability in floods and droughts. Results show that the changes in flood and drought characteristics are significantly linked to modes of climate variability in the Pacific, Indian, and Atlantic Oceans. Although flood and drought characteristics are significantly correlated, the influences of large-scale climate variability on them are non-linear. Meanwhile, local-scale factors impacting floods and droughts are variable throughout the sub-continent. Our results highlight the role that changes in rainfall, soil moisture and temperature play across the major watersheds in sub-Saharan Africa.

How to cite: Ekolu, J., Dieppois, B., Eden, J., Tramblay, Y., Villarini, G., Mahe, G., Paturel, J.-E., and van de Wiel, M.: Decadal to multidecadal variability in long- and short-lived hydrological extremes in sub-Saharan Africa, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8209, https://doi.org/10.5194/egusphere-egu22-8209, 2022.

08:51–08:58
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EGU22-4389
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ECS
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Virtual presentation
Zuzana Bešťáková et al.

The study deals with links between drought and atmospheric circulation in different parts of Europe (Western Europe, Central Europe, Eastern Europe, Northern Europe, and Southern Europe) during 1950–2019. The links are evaluated using drought characteristics (based on a difference between potential evapotranspiration and precipitation) calculated from gridded EOBS data and atmospheric circulation types that were classified using daily sea level pressure patterns obtained from the NCEP-NCAR reanalysis. Circulation types supporting drought in warm half-year are identified, and we analyse changes in their occurrence in the period after 1950, seasonal changes, and the connection with drought trends in individual European regions.

How to cite: Bešťáková, Z., Kyselý, J., and Lhotka, O.: Links between drought and atmospheric circulation types during 1950-2019, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4389, https://doi.org/10.5194/egusphere-egu22-4389, 2022.

08:58–09:05
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EGU22-12411
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ECS
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Virtual presentation
Zhixin Zhang et al.

Solar activity and internal climate modes (e.g., ENSO and PDO) have significant effects on extreme climate events and streamflow variability. As the roof of the world and the water tower of Asia, the Qinghai-Tibet Plateau (QTP) is highly sensitive to climate change. Therefore, it is of great significance to study the relationship between extreme hydrometeorological events of the QTP and climate change for global hydroclimate research. In this study, we analyzed the spatiotemporal variation and significant oscillation period of several hydrometeorological variables such as extreme precipitation indices (EPIs), extreme temperature indices (ETIs) and annual runoff based on the observation data of hydrometeorological stations in the QTP during 1962–2019 using Sen’s slope estimator, Mann-Kendall test and continuous wavelet analysis (CWT). And the teleconnection patterns and the leading–lag relationship between solar activity, internal climate modes and these hydrometeorological variables were evaluated using wavelet coherence (WTC). The result showed that QTP has been wetter and warmer in the past 58 years. The EPIs mostly mutated around 2010, and the increase was more pronounced after that; while the ETIs mainly mutated in the late 20th century. In terms of spatial distribution, the EPIs (except consecutive dry days) decreased from southeast to northwest; while distribution of ETIs was much more complicated. The extreme warm and cold indices showed a significant increasing and decreasing trend, respectively. The annual runoff of natural rivers in the QTP showed an increasing trend, and suddenly changed around 2000. EPIs had significant periodicities at 2–4-year band and 4–7-year band, while the significant periodicity of ETIs was mainly concentrated in the 2–4-year band. In addition, the annual runoff of natural rivers had significant periodicities in the bands of 2-4 years, 4-7 years and 7-11 years. Hydrometeorological variables had higher correlations with EI Niño-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) than with sunspot number (SSN). Solar activity first affects internal climate variability and then sequentially transfers this influence to meteorological and hydrological variables. This study has important implications for water resources management, flood control, climate feedback, ecosystem restoration, and the well-being of surrounding residents and sustainable development at the QTP.

Keywords: climate change; extreme climate events; runoff; Qinghai-Tibet Plateau; spatiotemporal variability; wavelet analysis

How to cite: Zhang, Z., Zhang, L., Liu, Y., and Jin, M.: Combined influence of solar activity and internal climate modes on long-term hydro-climatic variability in the Qinghai-Tibet Plateau, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12411, https://doi.org/10.5194/egusphere-egu22-12411, 2022.

09:05–09:12
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EGU22-13363
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Virtual presentation
Kwok Pan Chun et al.

Precipitation extremes are commonly linked with land use types. The UKCP18 Convection-Permitting Model (CPM) Projections at 5km high resolution simulation provide opportunities to investigate probable relationships between precipitation extremes and land use types. Changes in the duration and severity of extreme precipitation events can be linked to landscape characteristics, which affect the risk of rapid and local hydrological hazards.

Based on publicly accessible data and a standard approach, Local Climate Zones (LCZs) provide coherent descriptions of the form and function of urban landscapes. From the World Urban Database and Access Portal, the LCZ is used to translate relevant land attributes to urban canopy parameters for climate and weather modelling applications at appropriate scales. Using the Severn River Basin as a case study, we use LCZ data to calculate urban fractions to investigate the roles of urban land types to the extreme distribution parameters.

In conjunction with the LCZ data, the Corine Land Cover (CLC) and the Moderate Resolution Imaging Spectroradiometer (MODIS) datasets are used to benchmark how future changes in rainfall intensities and seasonal patterns might be related to land use. The results are used to generate possible hypotheses to run different CPM models based on the LCZ data.

Based on these findings, we present a novel land-use-based approach for water hazard management addressing hydrological risk connected to regional climate resilience. For management authorities and infrastructure owners, precipitation extreme risk related to land use is critical for their long-term investment planning. The proposed methodology would be advantageous to many UK water regulators and stakeholders in generating more informative precipitation extreme estimations based on land use, for the high greenhouse gas emissions scenario RCP8.5.

How to cite: Chun, K. P., Fan, P., He, Q., Dieppois, B., Danaila, L., Quinn, N., Klaus, J., Toker, E., and Yetemen, O.: Exploring links between precipitation extremes and land use types through the UK Convection-Permitting Model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13363, https://doi.org/10.5194/egusphere-egu22-13363, 2022.

09:12–09:19
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EGU22-444
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ECS
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Virtual presentation
Athira Krishnankutty Nair and Sarmistha Singh

Spatio-temporal variability of Indian Summer Monsoon Rainfall (ISMR) is responsible for extreme events like floods and droughts across India. In recent decades, the incidence of extreme precipitation events during ISMR is increased significantly, which are primarily linked to climatic variables like El Niño Southern Oscillation (ENSO), Equatorial Indian Ocean Oscillation (EQUINOO), Pacific Decadal Oscillation (PDO), and Atlantic Multidecadal Oscillation (AMO). In this study, extreme precipitation indices (EPIs) like consecutive dry days (CDD), consecutive wet days (CWD), maximum consecutive 5-day precipitation (Rx5day), and 95th percentile (R95p) have been considered to explain the characteristics of ISMR extremes. Moreover, a regional analysis has been carried out using the multiple wavelet coherence method to determine the coupled association of climatic oscillations with EPIs. Here, two-, three-, and four- climatic variable combinations have been applied to identify the best combination which explains the fluctuations of ISMR extremes all over India. Results indicate that two or more climatic oscillations could be sufficient particularly, AMO-ENSO-EQUINOO and AMO-ENSO-PDO are the best combinations to explain the variability of ISMR extremes across India. Apart from this analysis, wavelet decomposition and reconstruction analysis have also been performed to understand the scale-specific variability of the spatial-extreme precipitation. More than half of India had a significant correlation between reconstructed modes of ISMR extremes and climatic oscillations at interdecadal and multidecadal scales (8-16 and 16-32 -years), despite their interannual periodicities. This indicates that the non-stationary behaviour of the ISMR extremes was strongly associated with climatic variables at higher scales. 

How to cite: Krishnankutty Nair, A. and Singh, S.: Identification of combined influence of climatic variables on indian summer monsoon rainfall extremes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-444, https://doi.org/10.5194/egusphere-egu22-444, 2022.

09:19–09:26
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EGU22-551
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ECS
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Virtual presentation
Sidhan Valiya Veetil and Sarmistha Singh

Extreme meteorological events, such as droughts, are strongly influenced by large-scale climatic oscillations. Since India is one of the most drought-prone countries, comprehensive knowledge of the teleconnection of the climatic oscillations is very helpful towards developing precise drought prediction models. For evaluating the association between climatic indices and drought indices, the interdependency among the climatic oscillation time series has not been addressed well in previous studies. Hence in this study, an elaborate analysis is done in a time-frequency space using the variants of wavelet analysis such as Wavelet Coherence Analysis (WCA), Multiple Wavelet Coherence Analysis (MWCA), and wavelet reconstruction method. The study has used Five major climatic oscillations namely El Niño Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), Atlantic Multidecadal Oscillation (AMO), Indian Ocean Dipole (IOD), and Equatorial Indian Ocean Oscillation (EQUINOO), and a PET-based drought index, called Standardized Precipitation Evapotranspiration Index (SPEI) at four time-scales. The results from the analysis show that the interannual variability (2-4 years) of Indian droughts are primarily influenced by ENSO while the drought variability at 4–8-year time scale is influenced by the combined effect of PDO and EQUINOO. Similarly, the interdecadal variability (16-32 years) of Indian drought is dominantly influenced by PDO and IOD. AMO has not shown any significant association at any scale. Moreover, the droughts in Northwest and North Central India are strongly influenced by climatic oscillations. Further, the teleconnection pattern doesn’t significantly vary with the different timescale of drought. The study will help the hydrologists to enhance the understanding of the connection between climatic oscillations and Indian droughts and thereby better prepare for the impending droughts.

How to cite: Valiya Veetil, S. and Singh, S.: Multi-scalar association between large-scale climatic pattern and droughts in India , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-551, https://doi.org/10.5194/egusphere-egu22-551, 2022.

09:26–09:33
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EGU22-12763
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ECS
Hristo Popov and Jelena Svetozarevich

Climate fluctuations are highly dependent on changes in atmospheric circulation. The physical properties of air masses and their geographical distribution are of great importance because they determine the weather over large areas.

The North Atlantic Oscillation (NAO) is the most significant mode of natural climate variability in the Northern Hemisphere. It has a major impact on weather and climate in the North Atlantic and mainland Europe. There are two phases of NAO, positive and negative. When it is positive in Europe, warmer and wetter weather prevails. When it is negative, the weather in Europe is colder with more rainfall.

The Republic of Serbia is located in Southeastern Europe, in the western part of the Balkan Peninsula, the northern part of the country is located in the Middle Danube Lowland, the Sava Valley and the Tisza Valley. In the middle part are the river valleys of Drina, Kolubara and Morava. In the southern part of the country are occupied by mountains up to 2000 m high.

The aim of the article is to study the current changes in seasonal precipitation in the Republic of Serbia. For this purpose, data from 15 climate stations were evenly distributed over the territory and the influence of the NAO during the winter months. Three of the stations are mountainous - located over 1000m. The rest are alpine with lower altitude. The data is for seasonal values 1990-2019 were obtained from NIMH Serbia.

In structure of the research introduction presents the topic, tasks and bibliography. The Data and Methods section shows the geographical and climatic features of the study area and explains the methods. The next section provides results on seasonal changes and the impact of NAO. The conclusion shows the main results we have reached.

Key words:  NAO, climate change, seasonal precipitation, Republic of Serbia

How to cite: Popov, H. and Svetozarevich, J.: Current changes in seasonal rainfall and the impact of the NAO in Serbia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12763, https://doi.org/10.5194/egusphere-egu22-12763, 2022.

09:33–09:40
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EGU22-9659
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On-site presentation
Xin Li et al.

In the context of the current ocean-atmosphere cycle anomaly, exploring the potential teleconnections between climate indices and regional drought can help us know the variability of natural hazards more comprehensively to cope with them. This study explores the spatiotemporal patterns of drought and its multi-scale relations with typical climate indices in the Huaihe River Basin, China. The spatiotemporal variabilities of meteorological drought are identified using Empirical Orthogonal Function (EOF) and Continuous Wavelet Transform (CWT). The Cross Wavelet Transform (XWT) and Wavelet Coherence (WTC) analysis are used for investigating the multi-scale linkages between seasonal drought and climate indices, including Arctic Oscillation (AO), Bivariate El Niño–Southern Oscillation (ENSO) Timeseries (BEST), North Atlantic Oscillation (NAO), Niño3, Southern Oscillation Index (SOI), and sunspot number. Seasonal Standardized Precipitation Index (SPI)-3 during 1956-2020 are investigated separately for winter and spring seasons. We found that NAO mainly affects the interdecadal variation in spring drought, while AO and Niño3 focus on the interannual variation. In addition, Niño3 and SOI are more related to the winter drought on interdecadal scales. Our results prove that the onset, process, and intensity of El Niño or La Niña events influence the dryness and wetness conditions in the Huaihe River Basin. The results are beneficial for improving the accuracy of drought prediction, considering taking NAO, AO, and Niño3 as predictors for spring drought and Niño3 and SOI for winter drought.

How to cite: Li, X., Fang, G., Zhang, Z., Arnault, J., Wen, X., and Kunstmann, H.: Spatiotemporal Patterns of Drought and Multi-scale Linkages of Seasonal Drought to Climate Indices: A Case Study in the Huaihe River Basin, China, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9659, https://doi.org/10.5194/egusphere-egu22-9659, 2022.

09:40–10:00
Discussion

Wed, 25 May, 10:20–11:50

Chairpersons: Jean-Philippe Vidal, Bastien Dieppois

10:20–10:21
Part 2: Recent and Future changes in hydroclimate

10:21–10:28
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EGU22-6158
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ECS
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On-site presentation
Simon Moulds et al.

The ability to predict the frequency and magnitude of flooding at lead times of 1 to 10 years is of great interest to governments and institutions responsible for flood risk management. However, at these lead times there is significant uncertainty about dynamical changes in atmospheric circulation. The current generation of models underestimate the predictable signal of the North Atlantic Oscillation (NAO), the principal mode of variability in North Atlantic atmospheric circulation, leading to low confidence in predictions of regional precipitation and flooding. Recent work has shown that by post-processing a sufficiently large model ensemble, decadal variations in North Atlantic winter climate can become highly predictable (Smith et al., 2020). Here, we investigate whether this NAO-matching technique can be used to improve the skill of flood forecasts at decadal lead times in the United Kingdom. We use a large ensemble of decadal hindcasts consisting of 169 members drawn from CMIP phases 5 and 6, and observed flood records for the period 1960-2015. Following Smith et al. (2020), we adjust the variance of the raw ensemble mean NAO to match that of the observed predictable signal, then select the ensemble members showing the lowest absolute difference with the variance-adjusted ensemble mean. Working only with the selected members (n=20), we supply the ensemble mean precipitation and temperature to a distributional regression model to predict the occurrence and magnitude of winter floods at lead times of 1 to 10 years. We compare these predictions with those from an equivalent model which uses predictors drawn from the full ensemble (n=169) to assess the improvement in predictive skill. Our preliminary results suggest that NAO-matching shows promise at improving decadal flood predictions in northern Europe.

Reference

Smith, D.M., Scaife, A.A., Eade, R. et al. North Atlantic climate far more predictable than models imply. Nature 583, 796–800 (2020). https://doi.org/10.1038/s41586-020-2525-0.

How to cite: Moulds, S., Slater, L., and Dunstone, N.: Improving decadal flood prediction in northern Europe by selecting ensemble members based on North Atlantic Oscillation skill, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6158, https://doi.org/10.5194/egusphere-egu22-6158, 2022.

10:28–10:35
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EGU22-13310
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ECS
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On-site presentation
Margarita Saft et al.

The internal dynamics of a catchment can be shifted by multiyear dry periods. While there is consensus that annual streamflow decreases for a given annual rainfall in the case of multiyear dry period significantly more than during isolated dry years (thus representing a shift in hydrologic response), the mechanism of this shift remains debated. As the hydrological shifts were investigated on an annual and, to a lesser extent, seasonal scale, little is known regarding what parts of the flow regime (e.g. high flows, low flows, recessions) are affected and how. An event-scale analysis using process-linked hydrologic metrics (or signatures) can reveal hidden patterns in catchment response to multiyear drought and shed light on the otherwise hidden hydrological processes. Additionally, understanding whether some parts of flow variability experienced a more pronounced impact from the drought may be important for the water management decision-making. Here we investigate long-term changes in catchment response on daily to sub-monthly timescales to aid both hydrological processes understanding and water management practice.

We calculate over 30 hydrologic signatures characterising different aspects of flow regime and hydrological processes before, during, and after a decade-long drought and compare the results.  The signatures are calculated with the Toolbox for Streamflow Signatures in Hydrology (TOSSH) which combines signature sets from several earlier studies. We use a well-known multiyear drought, the Millennium Drought (MD) in Australia as our case study. This drought spanned ~13 years (1997-2009) and affected over 1 million square kilometres of land including 156 semi-natural study catchments in Victoria.

Our results suggest that on average both high and low flows were affected in similar proportion while the shape (i.e. slope) of the flow duration curve was largely preserved. The tendency to generate less runoff for a given rainfall has been demonstrated in a range of signatures from event to total flow volumes and thus is independent of the timescale. When analysing signatures related to catchment storage, we observe that the decline continues post-drought. Baseflow index and recession signatures show some evidence of multiyear catchment storage buffering. There is also evidence of lower hydrologic connectivity in the hillslopes affecting the event runoff. However, there are marked differences in signature behaviour between different catchments reflecting the differences in catchment internal structure and dominant hydrologic processes.

How to cite: Saft, M., Peel, M., Fowler, K., and Peterson, T.: What can hydrologic signatures teach us about a multiyear drought?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13310, https://doi.org/10.5194/egusphere-egu22-13310, 2022.

10:35–10:42
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EGU22-7748
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ECS
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On-site presentation
Cordula I. Wittekind et al.

In England, the priority catchment project focuses on developing innovative solutions to ensuring a clean and plentiful supply of water and environmental protection. Understanding the impacts of climate change on streamflow and water availability will ensure resilient management solutions into the future. The latest 12-member dynamically downscaled perturbed parameter ensemble of regional climate model projections (PPE-RCM) is part of the country specific UK Climate Projections UKCP18. In this study it was applied to estimate future changes in streamflow in an application of a new, revised version of the Soil and Water Assessment Tool (SWAT+) to two contrasting priority catchments in England. Both catchments are influenced by high rates of freshwater withdrawals but differ in their natural hydrological regimes and geographies. One is a wet coastal catchment with steep slopes while the other is a dry lowland catchment. Modelled impacts on natural monthly flows and flow duration statistics until the 2080s under the 12 member PPE were compared to those from 18 members of the euro-CORDEX initiative. Both ensembles are available for emissions pathway RCP8.5. To cover a broad range of scenarios, we also modelled the impact of the lower emissions (RCP4.5 & RCP2.6) euro-CORDEX projections.

SWAT+ performs well in simulating natural flows during the validation period in both catchments. The PPE estimates are consistently drier than euro-CORDEX. It projects streamflow in the coastal catchment to increase in seasonality with higher winter and lower summer flows, while streamflow in the dry lowland catchment is projected to decrease across all months apart from February. In the dry lowland catchment, the euro-CORDEX under RCP8.5 predict the strongest decreases in streamflow for June at -13%, while the PPE projects beyond -20% decrease throughout June to September. The climate change signal in the coastal catchment is less clear. The PPE projects winter streamflow to increase by between 5% to 36% while the euro-CORDEX under RCP8.5 predict increases between 13% to 23%, summer streamflow is projected to decrease by -16% to -23% and -0.5% to -4% respectively. RCP2.6 and RCP4.5 represent a mixed result with rarely beyond 10% change and more months with increasing trends than under RCP8.5. The different emissions pathways largely agree on increasing high flows and decreasing low flows in the coastal catchment. For the lowland catchment both ensembles driven by RCP8.5 project decreases across the whole flow duration curve while RCP 2.6 and 4.5 project medium to high flows to increase and low flows at Q70 and Q95 to largely stay the same.

This study suggests the need to adapt environmental protection and water withdrawals to decreasing water availability across the whole year in the lowland catchment and to pronounced changes in streamflow timing in the coastal catchment. To understand a broader range of climate impacts the UKCP18 PPE-RCMs should be used with other projections. However, they represent high-end warming scenarios translating into strong hydrological response, in particular streamflow decreases, that other ensembles might not capture, providing further insights into the challenges that water management may face.

How to cite: Wittekind, C. I., Charlton, M. B., Strauch, M., Witing, F., and Klaar, M. J.: Climate change impacts on river flow in England: a comparison of the UKCP18 and euro-CORDEX regional climate projections, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7748, https://doi.org/10.5194/egusphere-egu22-7748, 2022.

10:42–10:49
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EGU22-7165
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Virtual presentation
Frederiek Sperna Weiland et al.

Hydrologic variability is expected to change throughout Europe due to climate change. However, ensemble projections of future changes in discharge show large variation because of the uncertainty in climate projections. The robustness of the change signal can potentially be improved by performance-based weighting. Here we analyze future change projections from an ensemble of three hydrological models (CWatM, LISFLOOD and wflow_sbm) forced with climate datasets from the Coordinated Downscaling Experiment - European Domain (EURO-CORDEX). The experiment focusses on nine river basins spread over Europe. The basins have different climate and catchment characteristics that strongly influence the hydrological response. We evaluate the ensemble consistency, the geographical variation therein and apply two weighting approaches; (1) the Climate model Weighting by Independence and Performance (ClimWIP) that focuses on meteorological variables and (2) the Reliability Ensemble Averaging (REA) that is here applied to catchment specific discharge statistics.

In Southern and Northern-Europe the ensemble consistency is high. There is a strong climate change signal. In Central Europe the differences between models are more pronounced. Analysis of the weighting method reveal that both weighting methods favor projections from similar GCMs and assign high weights to a single or few best performing GCMs.

How to cite: Sperna Weiland, F., Visser, R., Greve, P., Bisselink, B., Brunner, L., and Weerts, A.: Evaluating hydrologic change for a set of European catchments by performance-based weighting of an ensemble of hydrologic and climate models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7165, https://doi.org/10.5194/egusphere-egu22-7165, 2022.

10:49–10:56
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EGU22-7816
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ECS
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On-site presentation
Bastien Dieppois et al.

The El Niño-Southern Oscillation (ENSO) is the leading mode of tropical climate variability, with impacts on ecosystems, agriculture, freshwater supplies, and hydropower production spanning much of the globe. Most impact studies use a canonical representation of ENSO, as characterised by sea-surface temperature anomalies (SSTa) in the central-eastern Pacific. However, ENSO shows large differences from one event to another in terms of its intensity, spatial pattern and temporal evolution. For instance, while the 1997/98 El Niño displayed extreme SSTa in the eastern equatorial Pacific, the largest SSTa during the 2002/03 event were weaker and primarily confined to the central equatorial Pacific. These differences in the longitudinal location and intensity of ENSO events, referred to as “ENSO diversity”, are associated with different regional climate impacts throughout the world. The representation of such differences in ENSO spatial patterns in climate models thus strongly influence the skill of impact prediction systems. Here, we exploit the power of single model initial-condition large ensembles (SMILEs) from 14 fully-coupled climate models from both CMIP5 and CMIP6 (totalling over 500 simulations in historical and SSP-RCP scenarios) to examine the system trajectories, and identify future variations in the location and intensity of El Niño and La Niña events. We then quantify how contrasting pathways for ENSO event location, and their associated intensity, could alter seasonal precipitation anomalies throughout the world over the 21st century.

How to cite: Dieppois, B., Maher, N., Capotondi, A., and O'Brien, J.: How could uncertainty in future ENSO diversity influence assessments of seasonal precipitation anomalies over the 21st century? , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7816, https://doi.org/10.5194/egusphere-egu22-7816, 2022.

10:56–11:03
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EGU22-12767
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ECS
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On-site presentation
Kirsten Maria Florentine Weber et al.

Relative humidity (RH) over land has declined steeply since 2000. The drying signal is relatively consistent from the edge of the deep tropics to the mid-latitudes of both hemispheres, whereas regions equatorward and poleward show increasing RH trends. The drying trend observed in the gridded global humidity dataset, HadISDH, could not be captured by the CMIP5 climate models [1, 2].

The drying trend finds partial explanation through thermodynamic drivers. Global warming causes an increase in both latent and sensible heat in the atmosphere. Over land, the increase in latent heat is much lower than that of sensible heat. Due to slower warming rates over the ocean compared to land, not sufficient humidity is evaporated and transported towards the coast to keep RH over land constant [3].

Temperature and moisture in many regions are influenced by the atmospheric circulation, therefore can influence RH. In this study, we investigate the potential influence of atmospheric circulation on the observed regional RH changes. We have done this for selected regions with a strong RH trend (including the western US, eastern Brazil, Greenland's coastal areas, southern Africa, the Caspian Sea, Mongolia and Tibet). We firstly calculate correlation and regression coefficients between gridded and regional RH and a range of dynamical drivers (including the Northern and Southern Annular Modes, ENSO and the PDO). We also explored the relationship between regional RH and global fields of sea surface temperature (SST), sea level pressure (SLP), and wind from the ERA-Interim reanalysis. We find a significant relationship between RH and the dynamical drivers in many regions (for example with the ENSO in eastern Brazil), as well as the impact of small-scale atmospheric circulations on land cover change, which then impacts RH (for example evaporation over the Caspian Sea). We will present these results, and try to quantify the contribution of these drivers to recent trends.

[1] Willet et al. (2014), HadISDH land surface multi-variable humidity and temperature record for climate monitoring

[2] Dunn et al. (2017), Comparison of land surface humidity between observations and CMIP5 models

[3] Sherwood and Fu (2014), A Drier Future?

How to cite: Weber, K. M. F., Jones, J., Willett, K. M., Osborne, C., and Bryant, R.: Why is the atmosphere becoming drier? - An investigation of the role of dynamical drivers on recent trends in relative humidity, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12767, https://doi.org/10.5194/egusphere-egu22-12767, 2022.

11:03–11:10
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EGU22-9305
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On-site presentation
Julie Collignan et al.

In a context of global change, the stakes surrounding water availability and use are getting higher. River discharge has significantly changed over the past century. Human activities, such as irrigation and land cover changes, and climate change have had impact on the water cycle. This raises the question of how to separate the impact of climate change from the impact of anthropogenic activities to better understand their role in the historical records.

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 long land surface simulation. 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 –. The ORCHIDEE Land Surface Model is used to estimate the terrestrial water and energy balance for the past climate but assuming humans do not modify land surface processes. This is a first guess of evaporation and its evolution due to climatic factors. Not having reliable observations of the evolution of the actual evaporation, river discharge and atmospheric observations are used to reconstruct it. This provides estimates of the evolution of the catchment characteristic and the evaporation efficiency which can then be compared to the modelled natural system. The aim is to separate anthropogenic changes from the effect of climatic forcing. To better understand the sensitivity of our methodology we applyied modifications to the atmospheric forcing to see how specific climate variations impact the sensitivity of the Budyko detection.

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 over the past century which can not be explained by the climate forcing. This trend is consistent with changes in irrigation equipment and development of dams over the studied period. However when looking at decadal trends, climatic fluctuations take precedence over non-climatic trends. In a context of climate changes, the balance between these trends could change in the future. The methodology was extended to other areas in Europe. The clear non-climatic trends were especially significant in semi-arid climate.

How to cite: Collignan, J., Polcher, J., Bastin, S., and Quintana Seguí, P.: Identifying and quantifying the impact of climatic and non-climatic effects on river discharge, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9305, https://doi.org/10.5194/egusphere-egu22-9305, 2022.

11:10–11:17
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EGU22-601
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ECS
Elena Grek and Liubov Kurochkina

The research is devoted to the identification of the patterns in spatio-temporal variability of river runoff characteristics in the North-West Russia. Based on long-term observation series, trends in the runoff characteristics were calculated as well as the patterns of their spatial variability were analyzed.

Within the framework of the work, the river runoff characteristics for 3 long-term periods were analyzed: the previous (before 1966), modern (1966-2019) and future periods (2022-2099).

The results of our study showed increase amount of cases with maximum runoff rainfall flood being higher than spring runoff from the end of 1980s.Estimates on expected changes in the hydrological regime under the implementation of RCP 2.6, 6.0 and 8.5 scenarios are presented. The most significant changes were detected in winter runoff and maximum spring and rainfall runoff. It is shown that an increase in winter runoff should be expected for the study area, as well as a decrease in the maximum water discharge of the spring flood. At the same time, according to scenarios 6.0 and 8.5, by the end of the century, the maximum annual discharge is likely to be observed during the period of rainfall floods.

How to cite: Grek, E. and Kurochkina, L.: Recent and future trends of river runoff in the North-West Russia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-601, https://doi.org/10.5194/egusphere-egu22-601, 2022.

11:17–11:24
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EGU22-2724
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ECS
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On-site presentation
Lisa Jarosch and Traugott Scheytt

In 2018 a mass death of fish occurred in the storage basin Lohsa I which is located in the Upper Lusatia, Germany. Lohsa I is a former lignite mining pit, which is now mainly used for industrial water supply, flood defence and fishing. It was assumed that an inflow of anaerobic groundwater could have been the cause for this event as groundwater inflow was observed before. Additionally, the input of fresh water from the river Kleine Spree was missing in summer 2018. In the project RoBiMo (robot assisted inland water monitoring) at the TU Bergakademie Freiberg there is a focus on collecting and analysing water quality data and climate data with the aim to quantify groundwater - surface water interactions and identify the influence of climate change in Saxony.

With an annual mean temperature of 12.4°C the year 2018 was +1.3°C warmer than the former period from 2010 to 2017. Total precipitation in 2018 was 398 mm, only 61% of the average precipitation of the period between 2010 and 2017 (648 mm). These data were used to quantify the amount of groundwater inflow to the storage basin Lohsa I and the effect of climate change.

For 2018 a positive value of groundwater flow was determined which implies an inflow of groundwater. A calculation from 1996 to 2019 shows an overall net inflow of groundwater. The calculation figures out a strong coherence between the groundwater flow, precipitation and sea water level. Until 2018 groundwater inflow and outflow were balanced but since then it became more deficient. The model BOWAHALD was used to determine evapotranspiration and storage change. The linear trend of precipitation is decreasing whereas the trend for evapotranspiration is increasing. As a result, the storage basin Lohsa I experiences a net loss of water.

Based on the results from storage basin Lohsa I the water budget for Upper Lusatia is calculated. Less precipitation, heavy rainfall events and decreasing groundwater levels are predicted for this area. The Lusatian lakes with 23 post mining lakes and a water surface area of more than 14,000 hectares will be heavily affected by climate change. For 2018 a loss of water to the atmosphere through evapotranspiration of 1.18 x 108 m³ was calculated. It can be assumed that such warm and dry years as 2018 will occur more frequently in the future.

How to cite: Jarosch, L. and Scheytt, T.: Influence of climate conditions and lake characteristics on the former lignite mining pit Lohsa I, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2724, https://doi.org/10.5194/egusphere-egu22-2724, 2022.

11:24–11:31
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EGU22-11365
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ECS
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Virtual presentation
Hanna Bolbot and Vasyl Grebin

The water budget of a certain area for a certain time interval is one of the quantitative characteristics of the hydrological cycle, which reflects the objectively existing in nature relations between the inflow, losing, and change of humidity reserves.

The paper presents the results of calculating the components of the water budget of the Udy River Basin (the Siverskyi Donets River Basin) based on the available observation materials, and also describes their long-term dynamics. Total evaporation was calculated from the temperature and absolute humidity by the Konstantinov method. For the study, four meteorological stations data, which zones of influence belong to the studied basin, and the hydrological gauge the Udy River - Bezlyudivka data were used. In order to identify changes that have already occurred with the water body, it was compared the hydrometeorological characteristics of the present period (1991-2020) with the period of climatological normal (1961-1990).

Since meteorological stations observations characterize discrete values ​​of meteorological indicators at individual points, and hydrological gauges observations show integrated values ​​of water runoff related to the upper basin situated, meteorological data were reduced to their average values ​​in the river basin. For this purpose, the weighing method was used - the basin is graphically divided by the system of Thiessen triangles into zones of influence of a separate meteorological station within the studied basin. The amount of precipitation, temperature, and relative humidity were determined using the calculated weights coefficient.

The study of the water budget of the Udy River Basin revealed an increase in air temperature within the basin and the associated increase in the value of total evaporation, a decrease in spring flood runoff, and an increase in total runoff of the low-water period. It is determined that the annual runoff in the present period has decreased by 17%. The total amount of precipitation for the two study periods is characterized by the same amount, but there was a change in their distribution during the year. The amount of precipitation decreased in the period of spring flood at the present period compared to the period of climatological normal and increased in the low-water period.

How to cite: Bolbot, H. and Grebin, V.: The structure of the water budget of the Udy River (Ukraine) under the influence of present climate change, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11365, https://doi.org/10.5194/egusphere-egu22-11365, 2022.

11:31–11:50
Discussion