Influence of sub basins with dominant land covers on spatial and temporal variations of water balance components in the Sondu Miriu river basin, Kenya

Abstract

Understanding the dynamics of the land cover changes and behaviour of hydrological processes in the river basin is important in the sustainable management of water resources. However, there is limitation of data and information on the extent to which dominant land use types particularly tea plantations, forests and mixed farming affects water balance components in tropical river basins and Kenya in particular. The main objective of this study was to determine the influence of sub basins with dominant land covers on spatial and temporal variations of water balance components. The study was undertaken in a 3,450 km2 Sondu Miriu river basin located in the western region of Kenya in the period between 1960 and 2020. Hydrological SWAT model was used to estimate the key hydrological components in the sub basins dominated by tea plantation, forest and mixed farming. These sub basins were Kipsonoi for mixed farming, Timbilil for tea plantations and Kiptiget for forest cover. Meteorological data was obtained from the Kenya Meteorological Services (KMS) and Water Resources Authority (WRA). Further, historical river discharges data was obtained from WRA and Ministry of Water, Sanitation and Irrigation. It was observed that land uses and land covers have insignificant influence on the rainfall variability in the three sub basins. Negative relation between area under forest cover and rainfall with correlation r of -0.37 was shown in the sub basin dominated by forest cover. But increase in rainfall in the sub basins led to expansion of tea plantations and mixed farming hence positive relations and reduction of forest cover. The positive relationship between evapotranspiration and mixed farming, evapotranspiration and forests cover was low ranging between correlation r of 0.05 and 0.14 while in tea plantations very low negative relation was shown. The sub basins dominated by tea plantations, forest and mixed farming shown an insignificant impact on soil moisture.