Hydrological impacts of land cover changes in upper Athi River Catchment, Kenya

Land cover changes have significant impacts on hydrological processes at the watershed level. The objective of the study was to apply a rainfall-runoff model derived using Hydrologic Engineering Centre-Hydrologic Modeling System (HEC-HMS) to predict hydrological impacts of land cover changes in Upper Athi River Catchment, Kenya. The derived HEC-HMS rainfall-runoff model was first calibrated and validated in the period 1984-1990 using six events in the study area. Land cover data used in the study were obtained from Land sat TM images of the years 1984, 1988 and 2010. The hydrological impacts were predicted using the calibrated HEC-HMS model in the period 1984-2010. Changes in peak discharges and runoff depths at the outlet of the study area were used to quantify hydrological impacts of land cover changes. The land cover change detection between 1984 and 2010 revealed that agricultural land and built-up land increased by 8.67 % and 23.70 % while closed/open woody vegetation, broadleaved evergreen forest and rangeland decreased by 9.98 %, 2.52 % and “19.88 %” respectively. The HEC-HMS model performance was found satisfactory with mean values of coefficient of efficiency (COE) during calibration and validation of 0.9514 and “0.9003” respectively. Impacts of land cover change analysis between 1984 and 2010 showed that peak discharges and runoff depths increased by 4-23% and 6-18% respectively. The increase in peak discharges and runoff depths were associated with the increase in impervious surfaces resulting from agricultural and built-up lands. The HEC-HMS model is recommended for prediction of hydrological impacts of land cover changes in the study area.