Coevolution of Hydrological Cycle Components under Climate Change: The Case of the Garonne River in France

Abstract

Climate change is suspected to impact water circulation within the hydrological cycle at catchment scale. A SWAT model approach to assess the evolution of the many hydrological components of the Garonne catchment (Southern France) is deployed in this study. Performance over the calibration period (2000–2010) are satisfactory, with Nash–Sutcliffe ranging from 0.55 to 0.94 or R2 from 0.86 to 0.98. Similar performance values are obtained in validation (1962–2000). Water cycle is first analyzed based on past observed climatic data (1962–2010) to understand its variations and geographical spread. Comparison is then conducted against the different trends obtained from a climate ensemble over 2010–2050. Results show a strong impact on green water, such as a reduction of the soil water content (SWC) and a substantial increase in evapotranspiration (ET) in winter. In summer, however, some part of the watershed faces lower ET fluxes because of a lack of SWC to answer the evapotranspiratory demand, highlighting possible future deficits of green water stocks. Blue water fluxes are found significantly decreasing during summer, when in winter, discharge in the higher part of the watershed is found increasing because of a lower snow stock associated to an increase of liquid precipitation, benefiting surface runoff.

Hydrological Alteration Index as an Indicator of the Calibration Complexity of Water Quantity and Quality Modeling in the Context of Global Change

“…However, similar sensitive parameters are found as the base flow alpha factor or the groundwater delay. Previous studies [11,16,92] show similar sensitivity for both of these parameters indicating a direct relationship between the surface runoff and other compartments parameters.…”

“…Calibration is a crucial step on modeling, considering its impacts on model outputs and result interpretations [89]. For hydrological models, only the streamflow and the water balance is usually calibrated based on field records and previous studies [11,20,80,90]. For agronomic models, biomass production and crop yield help to calibrate the model [91].…”

“…According to Moriasi [13,74], we considered the performances of the model succeed when R 2 , is This study explores an alternative methodology to model water quantity and quality resources at multiple scales, for the first time, by coupling various data sources (agricultural, urban effluents, quality and quantity data) at the SUDOE scale-that has been never approached [101][102][103]. Previous studies made analysis on uncalibrated simulations [9] or calibrated only on streamflow [11]. For hydrological models, only the streamflow and the water balance are usually analyzed based on gauging station records and previous studies [8].…”

“…To conduct such cross-boundary water analysis in a context of global changes, the model deployed needs to (i) incorporate climate, (ii) conceptualize different types of water resources such as "blue" (surface and aquifers) and "green" (evapotranspiration and soil moisture) waters (cf. [10,11]), (iii) have a detailed representation of limiting nutrients and sediment dynamics, and (iv) integrate anthropogenic pressures such as agricultural, industrial, and urban inputs. Investing modeling methodology at large scale is also important in order to understand water and nutrient cycles, as well as watershed behavior.…”

“…The water balance is the difference between inputs (precipitation) and outputs (discharge and evapotranspiration) at the outlet of the watershed. However, even if the water balance is correctly simulated, it does not mean that the water in the different compartments (soil, shallow and deep aquifers, and the fluxes between these compartments) are corrected [11]. During the last decade, attempts have been made to calibrate the hydrological model on additional hydrological parameters than discharge in order to analyze the water distribution between the different compartments and fluxes inside the watershed [11].…”