The potential impact of future climate change on Lebanese river basin hydrology using scenarios

The importance of announced climatic changes and their term are still the object of uncertainties. This work analyses, through scenarios, different hydrological consequences related to rainfall variability. The methodology of such an approach is presented and is justified by the absence of regional simulated downscaled climatic data. The conceptual rainfall-runoff model, MEDOR, coupled to the stochastic model of rainfall in Lebanon, is used to estimate change in runoff by simulation of scenarios. The sensitivity analysis of the parameters of the rainfall stochastic model shows that only the rainy season parameters have a direct effect on the streamflow characteristics. Six scenarios test the response of the rainfall structure, with fixed MEDOR parameters, toward the duration of rainy events, their frequency, and the duration of the rainy season. A seventh scenario tests the sensitivity of one of the loss parameters of MEDOR in the hypothesis of a proportional variation of potential evaporation change. The analysed streamflow characteristics are: mean annual discharge, monthly distribution and sorted discharge curve. The different sensitivity coefficients related to the variation of the climatic parameters are estimated, thus allowing a direct comparison in terms of importance and impact on hydrological runoff.