Watershed modeling using integrated hydrologic information system -

Abstract

Projected climate changes are expected to influence the hydrologic regimes of most river basins and increase the vulnerability of water resources systems worldwide. Lebanon, with a typical Mediterranean and semi-arid climate, is expected to be equally influenced by projected climate change. In this context, the Litani River Basin is vulnerable to changes in precipitation and temperature. The need to assess these changes is critical for the development of adaptation strategies and management plans for the basin, particularly the Upper Litani River Basin (ULRB) which is considered the most stressed part of the overall river. The successful implementation of such an assessment requires the implementation of a National Hydrologic Information System (NHIS) framework and the development of a National Hydrologic Geodatabase (NHG) for the evaluation of catchment hydrology and water resources under various scenarios. As such, an integrated hydrologic and water resources model for the ULRB was established using the Soil Water Method (SWM) under the Water Evaluation and Planning (WEAP) model. The model was calibrated (1952-1962) and validated (1962-2010) against streamflow using an integrated WEAP-PEST approach. Upon testing, the model exhibited good performance. A trend analysis was conducted on the climatology and hydrology between 1960 and 2010. The results showed decreasing trends for both observed precipitation and streamflow and an increase in temperature. Projected climate change impacts on the hydrologic system were assessed, over the time period between 2011 and 2100, using 24 scenarios representing the combination of 5 statistically downscaled General Circulation Models (GCM’s) and 4 Intergovernmental Panel on Climate Change (IPCC) storylines in addition to 4 ensemble models (i.e. average GCM predictions by storyline). The most pessimistic and optimistic scenarios were found to be the ECHAM4-A1FI and the CSIRO2-B2, respectively. Under the most pessimistic scenario precipitation and streamflow trends were es