IWRA Proceedings

AbstractIntroduction Between 2003-2005 the Integrated and Dynamic Water Balance was made in El Salvador, in its component of quantification of superficial water resources. Having in mind the necessity to update it permanently was developed the systematization of the calculation processes, and the options of scenarios of land use, climatic variations and variations in demand were included. Subsequently was incorporated the system the calculation of the demand of the different types from consumption and the component of estimation of underground water charge. Like final result, the system determines the Index of Shortage at river basin level, which relates the total demand to the water availability, for any period. Objective. The objective to systematize the Water Balance in El Salvador is to make a periodical evaluation of the water resources, that allows to give guidelines of management, protection and control. Methods The system has been developed using Visual Basic.NET software, and for the spatial analysis were used SURFER, ILWIS and ArcGis programs. The process of the systematization start with the incorporation and updating of the data bases of precipitation, average temperature, relative humidity and average flows at monthly level. The calculation of precipitation and evapotranspiration of reference is made through of Krigging interpolation, giving like result grids at monthly level with values of the variable at cell level, with which the areal average value for the selected geographic unit is calculate. The calculation of the real Evapotranspiración considers the land use and the soil types of each river basin. Additionally the lost by evaporation in water bodies and urban zones are calculated. The run-offs are taken from flow database for the river basins that have registry, and for the river basins that do not have it, have been developed two methodologies: precipitation-run-off relation and regionalization, also having the possibility of introducing calculated data through hydrometeorological modelling. Like result, the storage change is determined, from which the underground water charge is calculated, considering the impermeable zones of each river basin for the hydrogeological map. The quantification of the demand has been made for the sectors human, agricultural, industrial, cattle, hotel, fish, thermal and ecological consumption, and projections have been made until year 2050 for each one of such, considering macroeconomic projections, with indices like the PIB and PIBA. Results As result the water balance is obtained of any river basin of the country, in any period of time from 1970 to the present year, and projected water balances are obtained to year 2050, with scenarios of land use changes, water demand changes and climatic variability. Also the Index of Shortage of each river basin is obtained, which make possible assess the state of water consumption in relation to the existing supply. Conclusion. The system appears like a tool of diagnosis of the current water resources and future possible scenarios, which allows to analyze protection and regulation policies and management of the resource.