HS2.4.2

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

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

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

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

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

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

Reference:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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