Hydrological Characterisation of Mediterranean Catchments

The alarming climatic and anthropogenic impacts call for urgent adaptation and mitigation measures and water management policies that should be more based on regional research by deepening the knowledge on the spatial and temporal variability of hydrological resources all over the Mediterranean.

A climatic, physiographic, and hydrological homogeneity across the Mediterranean has been detected but not yet confirmed. Mediterranean climate is known for its precipitation seasonality and the alternation of humid winters and dry summers which conditions rivers flow regimes, landcover, agriculture and consequently any water resources management plan. Several physiographic traits could be also observed across the Mediterranean, like the elevated and exposed karstic features, and the cultivated and managed areas. Hydrologically, global river regimes were classified based on monthly average flows only, and Mediterranean regimes were identified under 3 of the 15 global classes with a clear relation to Köppen’s Mediterranean climate.

Thus, we first studied the flow regimes of 55 Mediterranean catchments to verify if Mediterranean rivers fall into same regime class. Second, we characterised the Mediterranean hydrological response through different water balance functional models as advanced by Budyko, L’vovich and elaborated by Ponce & Shetty and Sivapalan. We also defined from the functional model results the total runoff and groundwater runoff gains as the ratio of the runoff coefficients to annual precipitation, a notion advanced by Ponce and Shetty and elaborated as a sensitivity to precipitation and called elasticity by Harman. The analysis of the runoff gains and elasticity across the Mediterranean and through the climatic and physiographic classes characterised furthermore the hydrological behaviour similarity and variability, and the competition between the water balance components of the Mediterranean catchments.

The water balance analysis highlighted the Mediterranean trend following the general climatic setting from the wet Northern region to the arid Southern region; it also showed hydrological homogeneity for mountainous karstic and snow influenced catchments which yield the highest baseflows and runoff coefficients, especially those located in moderate climate region. However, they are the least sensitive to the humidity index P/Ep which make their hydrological behaviour very interesting to study under RCP 4.5 or RCP 8.5 climate change scenarios.