HS2.4.1 | Understanding the links between hydrological variability and internal/natural climate variability

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.

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Convener: Bastien Dieppois | Co-conveners: Hayley Fowler, Klaus Haslinger, Jean-Philippe Vidal, Lisa Baulon
Orals
| Mon, 24 Apr, 16:15–17:55 (CEST)
 
Room 2.17
Posters on site
| Attendance Mon, 24 Apr, 14:00–15:45 (CEST)
 
Hall A
Posters virtual
| Attendance Mon, 24 Apr, 14:00–15:45 (CEST)
 
vHall HS
Orals |
Mon, 16:15
Posters on site |
Mon, 14:00
Posters virtual
Mon, 14:00

Orals: Mon, 24 Apr | Room 2.17

The oral presentations are given in a hybrid format supported by a Zoom meeting featuring on-site and virtual presentations. The button to access the Zoom meeting appears just before the time block starts.
Chairpersons: Bastien Dieppois, Lisa Baulon, Jean-Philippe Vidal
16:15–16:20
5-minute convener introduction
16:20–16:40
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EGU23-4242
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solicited
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On-site presentation
Projected Changes in Peak Discharge Across the Contiguous United States 
Gabriele Villarini and Hanbeen Kim

Floods affect many aspects of our lives, and our improved understanding of the processes driving the historical changes in this natural hazard can provide basic information to enhance our preparation and mitigation efforts. Here we analyze thousands of long-term streamgages across the contiguous United States and attribute the changes in flood extremes to precipitation and temperature. We then leverage these physical insights to assess the future changes in flooding using outputs from global climate models part of the Coupled Model Intercomparison Project Phase 6. We find that flood peaks are projected to change across the contiguous United States. This is true even when flood changes are not detected in the more recent decades, highlighting the current needs for incorporating climate change in the future infrastructure designs and management of the water resources.

How to cite: Villarini, G. and Kim, H.: Projected Changes in Peak Discharge Across the Contiguous United States, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4242, https://doi.org/10.5194/egusphere-egu23-4242, 2023.

16:40–16:50
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EGU23-10846
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ECS
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On-site presentation
Time of emergence of extreme floods and droughts over the north-eastern United States 
Mina Faghih and François Brissette

Natural climate variability is known to be an important source of uncertainty in climate risk assessment. This can pose a substantial obstacle to the implementation of adaptation strategies because it may mask the signal of climate change. In this study, the authors investigate how extreme flows in 133 catchments in the eastern and northeastern United States are affected by internal climatic variability. They evaluate the ratio of internal climate variability to anthropogenic climate change on projected future extreme streamflow using temperature and precipitation data from a single model initial-condition large ensemble (SMILE) at high spatial and temporal resolution. To better understand the role of internal climate variability and its impacts on the climate change signal, the authors use three different parametric and non-parametric tests to evaluate the time of emergence (TOE) of the climate change signal. The results are presented for three classes of catchment area: small (500 km2), medium (500-1000 km2), and large (>1000 km2). The findings suggest that the future intensity of both floods and droughts will gradually increase, with the expected increases in flood and drought signals being strongly influenced by catchment size. Small catchments are likely to see higher increases in flooding than the other catchment sizes, but weaker increases in extremely severe droughts. The size of the catchment also affects TOEs, with smaller catchments seeing earlier TOE for floods and later ones for droughts. These findings provide significant information on adaptation timelines.

How to cite: Faghih, M. and Brissette, F.: Time of emergence of extreme floods and droughts over the north-eastern United States, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10846, https://doi.org/10.5194/egusphere-egu23-10846, 2023.

16:50–17:00
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EGU23-6461
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ECS
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On-site presentation
Moisture sources and pathways of annual maximum precipitation in the Lancang-Mekong River Basin 
Shuyu Zhang, Junguo Liu, Deliang Chen, Guoqing Gong, and Gengxi Zhang

Extremely heavy precipitation leads to increasingly frequent floods, landslides, debris flow, storm surges, and other natural hazards in the Lancang-Mekong River basin (LMRB) that causes large amounts of economic loss and affected millions of residences. This study analyzed the spatial-temporal characteristics of the annual maximum precipitation (R1X) of the LMRB and identified the moisture sources and pathways conducive to the occurrences of these extreme precipitation events during 1965-2021. Results show that the R1X of the upstream region concentrated in July, while that of the downstream region mainly occurred from August to September. The regional mean R1X shows an increasing trend, especially after 2010. The moisture pathways of the historical R1X were identified through a Lagrangian back trajectory model and were classified into three clusters by the Self-Organize Map: West Pacific Ocean (WP), local evapotranspiration, and Bay of Bengal (BOB). BOB provided the main moisture source to the R1X of the LMRB which contributes 68.3% of the trajectories, while the local evapotranspiration and WP account for 20.4% and 11.3%, respectively. For most areas downstream of LMRB, the moisture from the BOB transported through the cross-equator flow is the main moisture pathways patterns. For the upstream of LMRB, the evapotranspiration from the local and neighboring terrestrial and oceanic surfaces provides the main moisture sources. For the east area of the downstream, R1Xs are high and mainly resulted from tropical cyclones bringing large amounts of moisture from the WP to the LMRB. As tropical cyclones moved northward under climate change, more extreme precipitation over the LMRB was fed by the moisture from WP, while those from the BOB is decreasing with the slowdown of cross-tropical flows.

How to cite: Zhang, S., Liu, J., Chen, D., Gong, G., and Zhang, G.: Moisture sources and pathways of annual maximum precipitation in the Lancang-Mekong River Basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6461, https://doi.org/10.5194/egusphere-egu23-6461, 2023.

17:00–17:10
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EGU23-15739
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ECS
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On-site presentation
Large-Scale Climatic Drivers of Flood Frequency across Sub-Saharan Africa 
Job Ekolu, Bastien Dieppois, Jonathan Eden, Yves Tramblay, Gabriele Villarini, Simon Moulds, Louise Slater, Gil Mahé, Jean-Emmanuel Paturel, Moussa Sidibe, Pierre Camberlin, Benjamin Pohl, and Marco van de Wiel

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. Nevertheless, the key climatic factors driving interannual variability in flood frequency remain poorly documented and understood. To address this research gap, we first compile information on large-scale climate drivers that may potential affect sub-Saharan African hydroclimate (e.g., El Niño–Southern Oscillation, Atlantic Multidecadal Variability). Then, using a new 65-year long daily streamflow dataset of over 600 stations in sub-Saharan Africa, a bootstrapped stepwise regression and relative importance analysis is applied to quantify the relative contribution of different ocean basins to interannual variability in flood frequency between 1950 and 2014. Results show that interannual variations in the frequency of flood events are significantly linked to different modes of climate variability in the Pacific, Indian, and Atlantic Oceans. These modes of climate variability together explain around 60% of observed interannual variation in seasonal flood frequency. The relative influence of each ocean basin, however, differs from one region to another. The Indian and Pacific Oceans, for instance, have significant influences on interannual variations in the frequency of floods between December and May across much of southern and eastern Africa. In western Africa, the Mediterranean and Atlantic Oceans appear to have a dominant influence between September and November. In central Africa, the relative influence of different oceans basins is seasonally variable. Using the best combination of Sea-Surface Temperature predictors, we then examine projected future trends using a large ensemble of climate models from the CMIP6 experiments.

How to cite: Ekolu, J., Dieppois, B., Eden, J., Tramblay, Y., Villarini, G., Moulds, S., Slater, L., Mahé, G., Paturel, J.-E., Sidibe, M., Camberlin, P., Pohl, B., and van de Wiel, M.: Large-Scale Climatic Drivers of Flood Frequency across Sub-Saharan Africa, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15739, https://doi.org/10.5194/egusphere-egu23-15739, 2023.

17:10–17:20
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EGU23-15586
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On-site presentation
Recent Changes in the Magnitude of Flood-Generation Mechanisms across Africa: Relative Contributions of Climate Change and Decadal Variability 
Jonathan Eden, Bastien Dieppois, Yves Tramblay, and Gabriele Villarini

African countries are highly vulnerable to floods, with several studies reporting an increase in mortality rate and exposure in recent decades. Therefore, to improve flood forecasting and associated resilience to such natural hazards, a better understanding of the dominant flood-generating mechanisms and their evolution across Africa is of paramount importance. According to a recent study, excess rains on saturated soils in western Africa, and long rains for catchments in northern and southern Africa, are the two dominant mechanisms, contributing to more than 75% of all flood events. While the dominance of flood-generating mechanisms was not reported to change significantly in recent decades, the magnitude of those events may have changed in response to changing rainfall patterns (wetter or drier average conditions) across Africa. Here, we first estimate how much the magnitude of events with excess rainfall on saturated soils and long rains have changed over the last 65 years, before examining the statistical relationship between these changes, globally warming temperatures, and “natural” modes of decadal climate variability (e.g., Atlantic Multidecadal Variability [AMV], Pacific Decadal Variability [PDV]). To do so, we use a non-linear extreme value modelling approach with multiple covariates, applied to multiple observational datasets (e.g., ERA5, REGEN) and large ensembles from the Sixth Phase of the Coupled Model Intercomparison Project (CMIP6). This study, therefore, contributes to further the understanding of recent flood hazards in Africa, and identifies regions that will likely become more vulnerable to climate change and its decadal variability over the decades to come.

How to cite: Eden, J., Dieppois, B., Tramblay, Y., and Villarini, G.: Recent Changes in the Magnitude of Flood-Generation Mechanisms across Africa: Relative Contributions of Climate Change and Decadal Variability, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15586, https://doi.org/10.5194/egusphere-egu23-15586, 2023.

17:20–17:30
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EGU23-5094
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ECS
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Virtual presentation
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Past and future changes toward earlier timing of streamflow over Pakistan from bias-corrected regional climate projections (1962–2099) 
Shahid Ali, Kam Jonghun, Kim Byeong-Hee Kim, and Akhtar Taimoor

Streamflow has fluctuated seasonally in Pakistan and surface warming has caused its seasonal change, sometimes resulting in a lack of water resources for agriculture. However, little is known about how the seasonal changes in the hydrologic regimes over Pakistan has been and will be persisted. Using daily streamflow records from four gag stations data and bias-corrected hydrological projections, this study assessed the past and future changes in streamflow timing along four major river basins of Pakistan (Upper Indus, Kabul, Jhelum, and Chenab). First, we simulated the VIC-river routing model to generate past and future daily streamflow data forced by simulated daily surface and base runoff data from six CORDEX-South Asia regional climate models (1962–2099). Second, we corrected minimum and seasonality bias in simulated daily streamflow data against the daily observational records. Third, we calculated half of the annual cumulative streamflows (HCSs) and center-of-volume dates (CVDs) of observed and bias-corrected simulated streamflow data to quantify seasonal changes in the hydrologic regime. Except for the Chenab River basin, observational records revealed a significant decreasing trend in CVD (i.e., an earlier onset of the wet season) over Pakistan basins over 1962–2019. Bias-corrected hydrologic projections revealed a decrease in CVD of 4.2 to 6.3 days across the four study river basins over the overlapped period. The average decrease in CVDs ranged from 5 to 20 days and 11 to 37 days in the near future (the 2050–2059 average) and the far future (the 2090–2099 average), respectively. We found that the hydrologic responses of all four basins are diverse with different magnitudes of CVDs despite a similar magnitude of near-surface temperature across the basins, highlighting the need for basin-specific water resources management and climate change adaptation policies.

How to cite: Ali, S., Jonghun, K., Byeong-Hee Kim, K., and Taimoor, A.: Past and future changes toward earlier timing of streamflow over Pakistan from bias-corrected regional climate projections (1962–2099), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5094, https://doi.org/10.5194/egusphere-egu23-5094, 2023.

17:30–17:40
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EGU23-15726
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On-site presentation
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Is multidecadal prediction of flood patterns possible for infrastructure planning purposes using the 10000 year cosmogenic isotope (10Be and 14C) record? 
Michael Asten and Ken McCracken

We compare spectral decomposition of flood data from three sites in Australia (south-east coast, east-inland, east-central) with the Southern Oscillation Index (SOI), and with those from the Brahmaputra River (Bangladesh) and Nile River (Egypt). All show clear evidence of spectral maxima at medium periods approximating 50, 85, 130 and 200 years, which correspond closely to the maxima in the power spectra of the cosmogenic 10Be and 14C observations obtained from ice cores with ages covering the past 10000 years.  We find that the Gleissberg cycle (85 yr period) for Australian sites is out of phase with that for the Brahmaputra River.   All sites also show spectral maxima at short periods 6-20 yr as expected from the ENSO cycle; flood associations varying over these short periods are generally accepted. We explore the possibility that the medium periods can be used to assist in the prediction of flood and drought activity several decades into the future.  We consider   the hypothesis of a correlation or causal relationship existing between solar activity (including its effects on the intensity of galactic cosmic rays   on the Earth) and flood cycles for the medium periods. 

 

The Australian SE coast and east-inland sites, and the Brahmaputra River, show strong medium-period maxima.  The phase of the medium periods is obtained by optimized fitting of multiple sine curves with periods obtained from the spectra; the Australian SE coast and east-inland sites show summed sine curves with high correlation.  The Brahmaputra River shows similar correlation at medium periods (in particular the Gleissberg 85-year period) but in opposite phase.

 

The Australian east-central site (Murray-Darling Basin) and the Nile River (Egypt) show only weak evidence for the medium-period maxima which suggests ocean proximity is a factor for these influences.  The short duration SOI record shows   weaker evidence for medium-period spectral maxima, and the Southern Annular mode (SAM) and Indian Ocean Dipole (IOD) show no obvious correlation with observed medium-period flood patterns at the selected sites.  We speculate that the strong medium-period flood patterns are associated with the solar and/or cosmic ray cycles, observed in the cosmogenic record, where the causative mechanisms are yet to be established.  We conclude that the association of floods in medium-period cycles in addition to the association with the better-known short period variations associated with the ENSO cycle, provides opportunity for empirical predictions of flood patterns over ~80 years, and for the further investigation of possible causative mechanisms linking solar phenomena to oceanic indices and multi-decadal flood patterns.

How to cite: Asten, M. and McCracken, K.: Is multidecadal prediction of flood patterns possible for infrastructure planning purposes using the 10000 year cosmogenic isotope (10Be and 14C) record?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15726, https://doi.org/10.5194/egusphere-egu23-15726, 2023.

Discussion
17:40–17:50
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EGU23-3535
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ECS
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On-site presentation
Local vs regionalised deep learning models for groundwater level simulations in the Seine basin. 
Sivarama Krishna Reddy Chidepudi, Nicolas Massei, Abel Henriot, Abderrahim Jardani, and Delphine Allier

This study aims to investigate the use of deep learning techniques, with or without data pre-processing for simulating groundwater levels. Two approaches are compared: (1) a single (local) station approach, where a separate model is trained for each station, and (2) a multi-station approach, where a single model is trained using data from multiple stations in the study area. In the latter approach, static catchment attributes and dynamic meteorological (precipitation and temperature) and climate (sea level pressure, etc) inputs are used to model groundwater levels in the Seine basin. By including static variables corresponding to (hydro)geological or geomorphologic watershed characteristics in the deep learning model, we aim to improve the accuracy of simulations and better understand the factors that influence groundwater levels in the Seine basin. Additionally, we are assessing the potential of using MODWT as a pre-processing method in both approaches. For both single-station and multi-station approaches, without including static variables, results show that MODWT pre-processing helps the models in extracting the relevant information which in turn improves the simulations. Additional ongoing works are being conducted including static/watershed characteristics to assess whther these could help improving the modeling results.

How to cite: Chidepudi, S. K. R., Massei, N., Henriot, A., Jardani, A., and Allier, D.: Local vs regionalised deep learning models for groundwater level simulations in the Seine basin., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3535, https://doi.org/10.5194/egusphere-egu23-3535, 2023.

17:50–17:55
Convener Conclusion

Posters on site: Mon, 24 Apr, 14:00–15:45 | Hall A

The posters scheduled for on-site presentation are only visible in the poster hall in Vienna. If authors uploaded their presentation files, these files are linked from the abstracts below, but only on the day of the poster session.
Chairpersons: Hayley Fowler, Klaus Haslinger, Lisa Baulon
A.63
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EGU23-2989
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ECS
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On-site presentation
A framework for attributing runoff changes based on a monthly water balance model: An assessment across China 
Yufen He, Hanbo Yang, Ziwei Liu, and Wencong Yang

During the last decades, significant changes in runoff (Q) have been reported in many regions, and attributing the changes is of great significance for water resource management. The conventionally used elasticity method based on the Budyko hypothesis neglects the impacts of climate seasonality on annual Q change (ΔQ), and it is not yet well understood how the climate change and anthropogenic activities influence seasonal Q. Therefore, we propose a framework based on the ABCD model to explicitly identify the effects of climate change and anthropogenic disturbance on annual and seasonal ΔQ, and further apply it in 191 catchments across China from 1960 to 2000. The trend in annual Q exhibits a significant (α= 0.05) decreasing trend in most northern catchments and increasing trend in some catchments of the lower reaches of Yangtze River and Southeast Basin. The trend in seasonal Q in the northern catchments shows decreasing trend during all seasons, while most in the southern catchments shows increasing trend especially in summer. Regarding the causes for annual ΔQ, climate change has positive and negative effects in 60 % and 40 % catchments, respectively, and is the dominant factor in the catchments of the Yangtze River Basin, Southeast Basin and Pearl River Basin. Human activities have positive and negative effects in 20 % and 80 % catchments, respectively, and are the dominant factor in north China. Precipitation is the dominant climatic driver in 72 % catchments. For the causes for seasonal ΔQ, climate change increases Q in southeastern catchments during all seasons, while it decreases Q in northern catchments during autumn and winter. Human activities decrease Q in more than half of the catchments except in winter. The climate seasonality cannot be ignored and our proposed framework is superior to the elasticity method in capturing the impacts of climate seasonality on ΔQ. The elasticity method causes more than 5 % deviation of the contribution ratio of climate change to ΔQ in 48 catchments. In addition, this framework is reliable on multi-annual timescales and provides important reference for water resource management.

How to cite: He, Y., Yang, H., Liu, Z., and Yang, W.: A framework for attributing runoff changes based on a monthly water balance model: An assessment across China, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2989, https://doi.org/10.5194/egusphere-egu23-2989, 2023.

A.64
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EGU23-3708
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On-site presentation
Development of Dynamic Drought Vulnerability Assessment Considering Global Climate Change and Regional Water Demand-Supply Networks 
Tae-Woong Kim, Min Ji Kim, Jang-Gyeong Kim, and Jiyoung Yoo

Globally, drought affects different types of regions and countries, making it one of the most devastating natural disasters in terms of impacts on agriculture and food security, ecosystems, human health, and water resources. As the importance of integrated drought management including disaster risk reduction, climate change adaptation strategies, and national water policies is emphasized internationally, it is important to develop an effective water management technology for proactive drought response rather than reactive drought management to cope with drought disaster. In this study, we propose an approach to dynamic drought vulnerability assessment that can be used to secure elasticity for water demand and supply during drought event and further respond to a preemptive drought. Drought response and management based on this dynamic drought vulnerability assessment technology has consistency in that it promotes an internationally pursued convergence strategy for climate change adaptation and disaster risk reduction. The dynamic drought vulnerability assessment is based on the water demand-supply linkage assessment in various types of droughts. In other words, this is a technology for improving the ability to respond to drought through flexible water supply in the actual drought events. Dynamic drought vulnerability assessment produces various types of drought vulnerability map considering various scenarios of drought occurrence and socio-economic pathways according to climate change. For example, when combining hydrological drought scenarios considering climate change (25 types), water demand scenarios according to social/economic/environmental changes (3 types), water supply scenarios of drought damage/sensitivity by region (4 types), storage ratio scenarios of dam and reservoir (12 types), at least 2100 scenarios are produced as database. In the future, these results can be used as a basis for scientific decision-making in preparing countermeasures to improve resilience to drought.

Acknowledgement: This work was supported by the Korea Environment Industry & Technology Institute (KEITI) through Water Management Innovation Program for Drought (No. 2022003610001) funded by Korea Ministry of Environment.

How to cite: Kim, T.-W., Kim, M. J., Kim, J.-G., and Yoo, J.: Development of Dynamic Drought Vulnerability Assessment Considering Global Climate Change and Regional Water Demand-Supply Networks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3708, https://doi.org/10.5194/egusphere-egu23-3708, 2023.

A.65
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EGU23-3771
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On-site presentation
Lagged correlation between soil water content and evapotranspiration along recent decades and across different land cover types of Europe 
Mehdi Rahmati, Alexander Graf, Bagher Bayat, Carsten Montzka, Christian Poppe, Jan Vanderborght, Harrie-Jan Hendricks-Franssen, and Harry Vereecken Harry Vereecken

The link between soil water content (SWC) and evapotranspiration (ET) is of great importance in ecohydrology, agroecosystem management, and land-atmosphere interaction of earth-system analysis. There is still a need to understand the key processes linking SWC and ET in different vegetated ecosystems, especially at larger scales. Therefore, in this work, we used wavelet coherence analysis to explore the long-term relationship between SWC and ET among the predominant land use types (cropland, evergreen needleleaf forest, mixed forest, open shrubland, wooden tundra, grassland, and mixed tundra) in Europe during the last four decades (1980-2020). To this end, first a principal component analysis was performed among the SWC and ET data from GLDAS, GLEAM, and ERA5-land, and the first component was then used for further analyses when the target variable was in demand. Using the first component, then, we averaged SWC and ET data over the pixels covered by each land use type. Then, for each land-use types, we averaged the data daily for each decade to account for a representative decadal year of daily data. Then, wavelet coherence analysis was conducted between those averaged data of SWC and ET for each land-use type. The results showed a negative correlation between ET and SWC for all land use types, with ET lagging behind SWC, with an average phase shift value of 134 days for grassland (the minimum) and 168 days for mixed tundra (the maximum). Converting the phase shift values to a time lag [lag = n/2 - phase shift for the case phase shift < -n/4 where n represents the period (1/frequency) of the signals] shows (Fig. 1) that ET controls SWC with a lag of 15 days in mixed tundra (the minimum) and 48 days in grassland (the maximum). Moreover, we applied Mann-Kendall trend analysis test and found that the lag between SWC and ET decreases in mixed and wooden tundras with a slope value of -2.4 days/year, while it increases in cropland and grassland with a slope value of 1.6 days/year. Although there is a significant downward trend in evergreen needleleaf forests (with a slope value of -0.3 days/year) and an increasing trend in mixed forests and open shrublands (with a slope value of 0.4 days/year), the lower slope values in these land use types indicate that the change is slower compared to grasslands, croplands, and tundras.

 

Figure 1- Temporal evolution of the lag between soil water content and evapotranspiration in the annual cycle in different land use types in Europe 

How to cite: Rahmati, M., Graf, A., Bayat, B., Montzka, C., Poppe, C., Vanderborght, J., Hendricks-Franssen, H.-J., and Harry Vereecken, H. V.: Lagged correlation between soil water content and evapotranspiration along recent decades and across different land cover types of Europe, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3771, https://doi.org/10.5194/egusphere-egu23-3771, 2023.

A.66
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EGU23-4663
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ECS
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On-site presentation
Effect of Snow on Streamflow Variability 
Juntai Han and Yuting Yang

With the ongoing climate warming, changes in intra-annual distribution, annual volume, and their inter-annual variability of streamflow have been key research topics of ever-increasing interest. For settling the question of how changing climate shapes streamflow dynamics, here, we used long-term (1950-2010) observations of monthly streamflow (Q) for 2960 global unimpaired catchments, combined with snowfall (SF) and precipitation (P) estimates from ERA5-Land to provide a global assessment of effect of snowfall on streamflow variability. Results showed that precipitation was the main control of intra-annual and inter-annual streamflow variability while the propagation process of variability would be regulated by snow. As the snowfall fraction (sf) decreased, the annual runoff coefficient decreased, while the timing of streamflow got advanced and the intra-annual distribution became more even. Besides, the inter-annual variability of streamflow shows a negative relationship with snowfall fraction. The negative relationship between streamflow inter-annual variability and snowfall fraction may result from the asymmetric hydrological effects of snowfall in the wet and dry years.

How to cite: Han, J. and Yang, Y.: Effect of Snow on Streamflow Variability, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4663, https://doi.org/10.5194/egusphere-egu23-4663, 2023.

A.67
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EGU23-4717
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ECS
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On-site presentation
Low resilience of fractured groundwater systems to climate change and human activities 
Jintao Su, Xin Luo, and Jimmy Jiao

Groundwater, as an essential and dynamic part of hydrosphere, sustains the water demands and livelihoods in diverse landscapes and ecosystems. Currently, understanding on groundwater responses to climate variability is less addressed in IPCC reports yet important for future projections of water resources and management. Recent studies demonstrate that aridity index and likely hydrogeological setting jointly control the climate resilience of groundwater regionally and globally. However, most of these studies are bounded to quaternary sedimentary aquifers (i.e., North China plain, U.S. plains, Nubia plains) subject to intensive agricultural activities. Compared with quaternary aquifers which is dominated by porous media, groundwater in fractured bedrocks flows faster because of smaller effective porosities. The discharge and recharge processes are therefore expected to be more sensitive to climate variability and anthropogenic activities (i.e., pumping, urbanization, and reclamation) in fractured aquifer, but the underlying mechanism remains unclear, mainly limited by the lack of mature theory to delineate the interplays between fractured aquifers, climatic processes and human forcings, and the scarcity of long-term observation in the fractured bedrock aquifers.

In this study, we leveraged the decadal weekly monitoring (1971-2000) of rainfall, potential evapotranspiration, groundwater table, and stream discharge the headwater catchments dominated by fractured aquifers. with and without major human disturbance. We identified the significantly lower resilience of these fractured groundwater systems to change climates and human activities. By examining the variations and phases of recharge and discharge (baseflow to the river channel), we concluded that the rapid recharge-discharge in the fractured bedrock groundwater might serve as an effective push-pull process to significantly lower the resilience of fractured groundwater systems to climate changes and human disturbance. Topographic metrics i.e., slopes and concavity, are not likely to influence the interplay between fractured groundwater system and climate/human forcings. Our results also highlight the potential teleconnections between the fractured groundwater system and long-term climate changes (i.e., El Niño-Southern Oscillation/Asian summer monsoon/ Asian winter monsoon). This study advances the understanding the role and behaviors of fractured groundwater systems under changing climate and human disturbance and pave the way for a sustainable groundwater management in the fractured groundwater systems from local to global scales.

How to cite: Su, J., Luo, X., and Jiao, J.: Low resilience of fractured groundwater systems to climate change and human activities, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4717, https://doi.org/10.5194/egusphere-egu23-4717, 2023.

A.68
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EGU23-5627
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ECS
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On-site presentation
Parameter Estimation to Penman Combination Equation in Stream Using Latent Heat Flux and Hydrometeorological Data 
Minwoo Park, Yoon-Jeong Kwon, Jae-Ung Yu, and Hyun-Han Kwon

Recently, floods and droughts have become more frequent due to climate change and climate variability, leading to an increase in uncertainty regarding water resources management. For reliable water resources management, it is necessary to estimate available water through the water budget analysis accounting for hydrologic circulation. However, evaporation loss in the stream is not fully considered in the water budget analysis for water resources planning in South Korea. Evaporation is a critical component of the hydrological cycle that is affected by energy exchange between the water surface and the atmosphere. Therefore, we used latent heat flux data obtained from the flux tower system to quantify evaporation. This study formulated a stream evaporation formula based on PCE(Penman combination equation) equation and estimated the associated parameters in the Bayesian modeling framework that can effectively consider evaporation loss in the entire water budget analysis. We expect that this study will contribute to water management planning by adopting the regionally calibrated PCE formula in the estimation of available water more effectively.

Acknowledgement : This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korea government(MSIT). (No. 2019R1A2C2087944)

How to cite: Park, M., Kwon, Y.-J., Yu, J.-U., and Kwon, H.-H.: Parameter Estimation to Penman Combination Equation in Stream Using Latent Heat Flux and Hydrometeorological Data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5627, https://doi.org/10.5194/egusphere-egu23-5627, 2023.

A.69
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EGU23-8150
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On-site presentation
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Atmospheric Circulations and Drought Conditions in British Catchments: Highlighting the Role of the East Atlantic Pattern 
Harry West, Nevil Quinn, and Michael Horswell

Drought events are influenced by a combination of both climatic and local catchment characteristics. In Great Britain the North Atlantic Oscillation (NAO) has long been recognised as the leading mode of climate variability, and studies have also noted the role of the East Atlantic Pattern (EA) as a secondary mode. This study aimed to develop an understanding of the combined influence of the NAO and EA on rainfall distribution and magnitude and the variable nature of meteorological to hydrological drought propagation. Initially, this study explores correlations between teleconnection indices and standardised precipitation and streamflow indices for 291 catchments across Great Britain, before focusing on nine case study catchments for further analysis. For each case study catchment, we use quantile regression and an analysis of drought frequency to explore the combined influence of the NAO and EA on drought conditions.

Through a convergence of evidence from these analyses we make three observations. Firstly, in the winter months both the NAO and EA exert an influence on drought conditions, however there is spatial variability in the relative influence of the NAO and EA; the NAO has a stronger influence in the north-west, whilst the EA has a stronger influence in the southern and central regions. Secondly, in the summer months, less distinctive spatial differences were found, with higher probability of drought conditions under NAO+ phases, which however can be enhanced or moderated by the EA. Finally, as a result of catchment characteristics there is spatio-temporal variability in the propagation of meteorological to hydrological drought. Our findings suggest that by considering the NAO and EA in combination, we can better describe climate and drought variability. We conclude by noting the potential implications our study has on the role of monthly teleconnection forecasts in water management decision making in Great Britain, and acknowledge the current limitations associated with incorporating such understanding.

How to cite: West, H., Quinn, N., and Horswell, M.: Atmospheric Circulations and Drought Conditions in British Catchments: Highlighting the Role of the East Atlantic Pattern, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8150, https://doi.org/10.5194/egusphere-egu23-8150, 2023.

A.70
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EGU23-12267
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On-site presentation
Hydrological variability of Finnish free-flowing rivers 
Karoliina Lintunen, Cintia Bertacchi Uvo, Petteri Alho, and Elina Kasvi

River discharges and ice cover strongly impact biotic and abiotic processes in fluvial environments. Hydrometeorological circumstances affect discharges and under climate change, they are changing in high-latitude areas of the globe. During the past decades, spring snowmelt has started earlier in Northern Europe, leading to a shift in the timing of floods and discharge peaks. Also, higher wintertime discharges have been measured. However, little is known about how these changes in the variability and trends have occurred during the past decades (up to 100 y.) and how they will evolve in the future.

The goal of this paper is to understand how the hydrological variability of free-flowing rivers has changed from the past to the present in Finland. To achieve the goal, long-term data on flood magnitude, frequency, and timing are statistically analyzed to identify the hydrological variability of Finnish free-flowing rivers. Previous works showed that discharge parameters work as reliable indicators for assessing long-term changes caused by climate change when combined with weather parameters, teleconnection patterns, and river ice data. Open-access data from 45 gauging stations in 25 different watershed areas were used. The timespan of datasets varies between 40 and 100 years. The results of this paper can be applied when future changes and adaptation methods related to river discharges are considered in the boreal-subarctic climate region.

How to cite: Lintunen, K., Bertacchi Uvo, C., Alho, P., and Kasvi, E.: Hydrological variability of Finnish free-flowing rivers, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12267, https://doi.org/10.5194/egusphere-egu23-12267, 2023.

A.71
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EGU23-13655
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ECS
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On-site presentation
Heat transfer in the Southern Baltic Sea 
Daniel Rak, Lidia Dzierzbicka-Głowacka, Waldemar Walczowski, and Anna Bulczak

The balance of energy supplied to the sea surface in the Baltic Sea proper is positive, which means that this region absorbs more energy than it releases to the atmosphere. Further transport of this energy in the form of heat is transported deep into the water column. It has been shown that differences between individual basins of the Baltic Proper appear along with the depth. The temperature signal, resulting from seasonal changes in the amount of solar energy supplied to the sea surface and the conditions of energy exchange between the sea and the atmosphere, propagates the fastest into the water column in the Gdańsk Deep, where it takes 37 days to a depth of 50 meters. In the Bornholm Basin, the speed of this signal is 71 days.

How to cite: Rak, D., Dzierzbicka-Głowacka, L., Walczowski, W., and Bulczak, A.: Heat transfer in the Southern Baltic Sea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13655, https://doi.org/10.5194/egusphere-egu23-13655, 2023.

A.72
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EGU23-16848
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On-site presentation
Atmospheric and oceanic influences on the hydrological scenarium southern Brazil in relation to extreme events observed in 2022 
Douglas Paulek, Cassia Paranhos, Camila Freitas, and Camila Carpenedo

After a long period of drought experienced in South America, which began in 2019 and lasted until 2021 for the southern region of Brazil, the hydrological scenario of this region presented positive precipitation anomalies throughout the year 2022. That anomalies resulted in the increase in the flow observed in the main river basins of the southern region of Brazil, which wanted to recover the storage volume of the reservoirs and social activities and ingestion, in addition to the occurrence of extreme events at Iguaçu Falls. Precipitation in the southern region of South America, especially in Brazil, is the result of different climatic phenomena. Its latitudinal (tropical) location means that this region is influenced by frontal systems, polar masses, Mesoscale Convective Complex (MCC) systems, and South Atlantic Convergence Zones (SACZ). In addition to also being influenced by the El Niño-Southern Oscillation (ENSO) phenomenon, which is associated with changes in the normal patterns of Sea Surface Temperature and trade winds in the Equatorial Pacific region, the Madden-Julian Oscillation (MJO), and others atmospheric and oceanic systems on global scales. This work presents a discussion about the anomalies in the atmosphere (geopotential height 250 hPa) and an analysis of the climatic phenomena that may have contributed to the precipitation anomalies observed during the months of May to October 2022.

How to cite: Paulek, D., Paranhos, C., Freitas, C., and Carpenedo, C.: Atmospheric and oceanic influences on the hydrological scenarium southern Brazil in relation to extreme events observed in 2022, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16848, https://doi.org/10.5194/egusphere-egu23-16848, 2023.

Posters virtual: Mon, 24 Apr, 14:00–15:45 | vHall HS

The posters scheduled for virtual presentation are visible in Gather.Town. Attendees are asked to meet the authors during the scheduled attendance time for live video chats. If authors uploaded their presentation files, these files are also linked from the abstracts below, but only on the day of the poster session. The button to access Gather.Town appears just before the time block starts.
Chairpersons: Hayley Fowler, Bastien Dieppois, Lisa Baulon
vHS.15
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EGU23-3659
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Virtual presentation
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How does the 'window' of overland flow generating rainfall react to Clausius-Clapeyron scaling? 
Bernhard Schmid

Rainfall on an infiltrating microcatchment or hillslope will trigger overland flow, if it is long and intense enough. It is, naturally, of interest to know, what 'enough' means in quantitative terms, i.e. with respect to a given soil and an intensity-duration-frequency (IDF) relationship of selected return interval.

Fully impervious surfaces excepted, an initial phase of the process exists, during which detention storage will be filled and water infiltrates into the soil. The end of that phase (if any) marks the lower limit to the overland flow generating rainfall 'window'. Further to the right of the IDF-curve longer events causing overland flow follow, until a point is reached, where no more overland flow forms, this time because the rainfall intensity has become too low to overcome infiltration. The interval between these two end points has been termed the 'rainfall window'. A closed form expression for its length is given subsequently, and its response to rainfall events subject to Clausius-Clapeyron scaling will be discussed. 

An IDF relationship of the form

is assumed, with r the rainfall intensity, td the storm duration and f the Clausius-Clapeyron scaling factor (parameters s = 0.0597 m and  b = 540 s in the examples below). Using a Green-Ampt type infiltration model and assuming p = 1, the following closed form expression has been derived:

with Ksv vertical saturated permeability and Sav averaged suction at the wetting front.

The Clausius-Clapeyron relationship, i.e. a 7% increase in rainfall depth per additional degree centigrade of warming, may yield an order of magnitude of what to expect from climate change. Here, f = 1.07 will be assumed for 1 K increase in temperature, and f = 1.14 for 2 K.

The examples given here use a present-day IDF relationship of 20 years' return interval (roughly valid in the Austrian Alps) and initial loss of 0.5 mm. The rainfall window was computed using soil data from Columbia sandy loam, Guelph loam and Ida silt loam. Future warming was assumed as 1.0 and 2.0 K, resp.

In the case of the most pervious soil of the three (Columbia sandy loam, vertical saturated permeability Ksv = 0.0139 mm/s) the (short) rainfall window showed a length of 22 min (present), 27 min (1 K warming) and 31 min (2K), an increase of 22% and 43%, resp.

The 'medium' soil, Guelph loam (Ksv = 0.00367 mm/s), started from a window length of 109 min (present), rising to 123 min and 138 min for 1K and 2K resp. (increases of 13% and 26%).

In case of the finest soil, Ida silt loam (Ksv = 0.000292 mm/s), the overland flow generating window of rainfall was longest and amounted to 44 h (present), 48 h (1K: 9% increase) and 52 h (17% increase).

In conclusion it may be stated that notable increases in the overland flow generating rainfall window are to be expected due to future warming. Overland flow events tend to become more frequent as more storms will qualify as triggers.

How to cite: Schmid, B.: How does the 'window' of overland flow generating rainfall react to Clausius-Clapeyron scaling?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3659, https://doi.org/10.5194/egusphere-egu23-3659, 2023.