IMPACT OF LAND USE CONVERSIONS ON WATER YIELD

Abstract

Trees use more water than shorter vegetation due to comparatively high interception and evaporation losses. These losses also vary with the different tree species and climatic conditions. In high elevations, trees could offset the interception losses by capturing horizontally driven fog into the catchment system. Therefore, it is important to study the hydrological processes which would help to estimate water use of different land cover types which in turn is required to find the effect of land use conservation on water yield.

Only two studies with limited duration have been carried out to find the effect of land cover on a few hydrological processes in 1977 and 1988. Therefore, a long-term research project has been carried out since 1993 at two sites, namely at Dodangolla and Horton plains, to monitor the hydrological processes in detail under different land use types. Home gardens, grass and Acacia are being selected at the low elevation site, while montane forests, grassland and Pinus are being selected for the high elevation site.

These two sites are instrumented with automatic weather stations which monitor rainfall at 5 minutes intervals and other climatological parameters at hourly intervals. Net rainfall gauges with tipping buckets are installed to measure interception. Soil moisture is being monitored with access tubes and neutron probes at the two sites. A fog collector is installed at the Horton plain site to measure the horizontally driven fog at hourly intervals.

The results from this study will be used to calibrate a water use model for different land use types. Once this is accomplished, the model can be used to predict the effect of land use conservation on water yield.