IWRA World Water Congress 2008 Montpellier France
1. Water availability, use and management
Adriana Maria Erazo
15 year of experience in hydric resources
System, Integrated and Dynamic Water Balance, Index of Shortage, Tool of
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.
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
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
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.
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.
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.
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.