THE EFFECT OF LAND USE DYNAMICS ON STREAM FLOW FLUCTUATIONS: A SWAT SIMULATION CONDUCTED IN A THIRDORDER WATERSHED OF CENTRAL HONDURAS

Abstract

In Honduras, as well as in many other developing countries, less than 60% of the population inHonduras has reasonable access to safe drinking water and its quality is decreasing at anaccelerated rate. This study consists of assessing the stream flow patterns after land use changesin the 4,200-ha Rio Calan Watershed of Central Honduras. Streamflow modelling was conductedusing SWAT (Soil and Water Assessment Tool), a computer-based program developed byUniversity of Texas to predict the impact of land management practices on discharge and waterquality at the watershed scale. This constitutes the first attempt to use SWAT under tropicalconditions in Honduras. To study the land use dynamics, three temporal land use covers: 1993, 1998 and 2000, weredeveloped from Landsat images. Additionally, three hypothetical land use covers were alsomodelled: pine trees, grass land and agriculture. As a first step, the model was calibrated withdata collected for 1 year in the field. Latter, the data bases containing: land use, soils, and climatedata were adapted with field data and information collected from local agencies. As a result, we obtained a 10-year hydrograph for each real and hypothetical land use covers.Around 600 ha of tropical broad leaf and pine forests (15% of the watershed area) wereconverted to subsistence agriculture from 1993 to 2000. SWAT simulations, showed that land useconversion caused a slight increase in streamflow values in the 10-year-hydrographs. Theagricultural cover, a hypothetical scenario, showed the highest value on streamflow during thepredicted time. The predicted stream values (SWAT outcomes) and one-year field measurementswere compared and a small disparity was observed. SWAT proved to be a powerful tool formodelling streamflow patterns. Work is still in progress to improve SWATs data bases toHonduran-tropical conditions.