Climate change and Land use/land cover (LULC) represent the two primary factors influencing the hydrology of a watershed. In this research, we explore the combined impact of alterations in climate and LULC on hydrological processes. This examination involves comparing the baseline period (1979-2005) with future conditions (2046-2072) within the Siliana catchment in Tunisia, utilizing the Soil and Water Assessment Tool (SWAT) hydrological model.
Future LULC scenarios are generated using Cellular Automata (CA)-Markov chain modelling, while climate change scenarios are derived from regional climate models (RCMs) developed within the coordinated regional climate downscaling experiment (CORDEX-Europe). To address bias, the so-called Cumulative Distribution Function (CDF) matching approach is applied using observed precipitation and temperature data. Subsequently, bias-corrected climate projections and future LULC scenarios are input into the SWAT model to evaluate changes in catchment hydrology, based on various hydrological indicators (such as monthly discharge and total water availability). Prediction uncertainty associated with changes in LULC, climate conditions, and SWAT model parameters is also assessed.
The findings indicate that the Siliana catchment area is projected to experience a warmer and drier climate, leading to altered hydrological conditions in the future. This climatic shift is expected to result in a significant decrease in rainfall, consequently reducing surface runoff, water yield, and groundwater levels. Moreover, the hydrological modifications are consistent with the observed temperature patterns in the catchment region. The anticipated rise in average temperatures will likely lead to a substantial increase in potential evapotranspiration (PET).
Regarding changes in land use and land cover (LULC), there is an expectation of a notable decline in pastureland and an increase in irrigated areas, shaping the future LULC composition relative to baseline conditions.
Interestingly, the impact of climate change alone is expected to have a more pronounced effect on hydrological responses compared to the combined influence of climate and changes in LULC. This suggests that modifications in land use within the Siliana catchment region lead to an attenuation effect marked by extended periods of high-flow events, a reduction in the intensity of peak high-flow events, and an increase in the occurrence of low-flow events.