Modeling soil water balance of an agricultural watershed in the Guinea Savannah Agro-ecological Zone; a case of the Tono irrigation dam watershed

Abstract

Water is the most significant of all the requirements for plant growth and development. Its availability or scarcity in the soil can denote a successful harvest, reduction in yield, or complete failure. Though Tono is a small community in the Kassena Nankana East Municipality in Upper East Region of Ghana, farmers in the area contribute significantly to the availability of food products in neighboring communities, and even in some parts of southern Ghana. However, changing climate and landscape dynamics are perceived to be the primary cause of decreasing water availability and responsible for the dwindling farming fortunes. The study therefore investigated the changes to soil water balance occurring within the Tono dam watershed, as well as changes to the landuse/landcover (LULC) of the area and its impacts on crop production using the Soil and Water Assessment Tool (SWAT). The LULC continues to change through anthropogenic activities thereby causing variations in the hydrological cycle over time. A 30-year period from 1984 to 2014 was used as the simulation period to run the model. Two (2) LULC maps and change scenarios for 1984 through to 2014 were assessed. The results revealed a relationship between landcover and the response to hydrology, in that, a decrease in landcover causes a decrease in surface water, soil moisture, and a corresponding infinitesimal decrease in evapotranspiration. The results showed a 17.6%, 9.6%, and 1.6% decrease in rainfall, soil moisture and evapotranspiration, respectively. The results showed the ability of the SWAT model to reveal spatio-temporal variation of the change in the landscape and the associated changes arising from climate change having significant effects on the Tono catchment.