Estimating runoff and soil moisture deficit in guinea savannah region of Nigeria using water balance method

Abstract

The estimation ofrunoff and soil moisture deficit in Guinea Savannah region using semi arid model based on soil water balance technique (SAMBA) was carried out. The input to the SAMBA model are daily rainfall, daily evapotranspiration. type and date of planting of crop, and soil parameters. The estimated runoff was validated with field measurement taken in a 67.23 ha catchment in the study area. The annual rainfall for the year under study (2009) is 1356.2 mm.· the estimated annual evapotranspiration, runoff and recharge are 638mm, I 32.93mm, and 447.8mm respectively. Recharge was experienced 23 days after a significant depth of rainfall was recorded. For the crop growth in the catchment, the soil was cropped with a pepper and the growth monitored from the planting to the harvesting. T~e crop enjoyed so much moisture throughout the growing period as Total Available Water in the soil is greater than Soil Moisture Deficit (TAW>SMD). The model results show that the larger percentage of the total annual rainfall was lost to evaporation and recharge during the growing season. The low runoff and high recharge are attributed to soil characteristics of the area and moderate terrain of the study area.