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Impact of Rainfall Spatial Variability on Runoff Using Swat Model

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Water resource management and hydrologic modelling studies are intrinsically related to the spatial processes of the hydrologic cycle. The ability of hydrological models to accurately predict water availability at a catchment outlet depends to a great extent on how well spatial input data describe the relevant characteristics. For this reason, proper implementation of these models requires decisions to be made about not only the size of the spatial grids such as DEM (Chaplot, 2005), land-use and soil map (Muttiah and al, 2001, Romanowicz and al, 2005) but also the rain gauge density.

Precipitation is the key input variable that drives flow and mass transport in hydrologic systems (Beven, 2001). Accurate spatial and time representation is essential to runoff prediction (Faur├Ęs et al, 1995). The sensitivity of watershed models to spatial rainfall variability is becoming a key issue, especially in semi-arid areas. Indeed, rainfall input is subject to uncertainty as a result of an imperfect knowledge of its spatial distribution.

In this study, our main objective is to assess the impact of spatial rainfall variability effect on runoff within a semi-arid catchment located in northern Tunisia using the Soil and Water Assessment Tool (SWAT). The simulations were realized using daily data collected over a 14-year period for eight rain gauges. The investigation is based on comparing the water discharge measured at the watershed outlet to those generated by the model from four different scenarios of gauge concentration.

Study area: The study site is the Sarrath River Basin, located in northwest Tunisia, presented in Fig. 11-1. The river originates in the semiarid Atlas Mountains of eastern Algeria. This region is part of the large Tunisian Medjerda catchment; it encompasses an area of 1520 km2 with an elevation range from 573 to 1350 meters and average slope steepness from 3 to 72 %.

Document Type: Research Article


Publication date: January 1, 2008

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