Analyzing the spatial and temporal variability of soil moisture content in Uganda

Abstract

Soil moisture content is a crucial hydro meteorological parameter in the hydrological processes such as evaporation, evapotranspiration, rate of runoff. Its observation can be used to monitor drought occurrence, flooding, and to some extent weather prediction. In Uganda, limited research about spatial and temporal variations of soil moisture content has been done. This is due to the absence of in situ soil moisture measurement networks and limited in situ soil moisture measurement instruments. The aims of this study are; 1) To examine seasonal changes in soil moisture over Uganda at different depths. 2) To examine trends in annual averages of soil moisture over Uganda at different depths. Soil moisture content data from GLDAS at different soil depths (0-10 cm, 10-40 cm, 40-100 cm, and 100-200 cm) was used in this study. To understand annual and seasonal variations of soil moisture at different depths over Uganda the Mann Kendall trend test was used. The spatial-temporal characteristics of soil moisture content at different depths over Uganda was archived by using Arc GIS software to generate the spatial-temporal map of soil moisture content over Uganda. The results show that 1). the spatial and temporal variations of soil moisture content at soil depth 0-10 cm align with the spatial and temporal distribution of rainfall over Uganda. 2). Also, the spatial variations of soil moisture content at soil depth 0-10 cm align with the spatial distribution of vegetation over Uganda. 3). There is a general decrease of annual and seasonal soil moisture content at all soil depths over the different regions of Uganda except for the Northern region which shows slight increase in soil moisture content at soil depth 100-200 cm in wet season of MAM and the Eastern region at soil depth 0-10 cm and 100-200 cm in the wet season of SON and 100-200 cm in the dry season of DJF. 4). The decline of annual soil moisture content is significant at all soil depths over Uganda. 5). The decline of soil moisture content in the wet season (MAM) is only significant at soil depths 0-10 cm and 10-40 cm. 6). The decline of soil moisture content over Uganda is not significant at all soil depths in the wet season of SON .7). The decrease of soil moisture content in the dry season (DJF) is only significant at soil depths 0-10 cm.8). The decline of soil moisture content is significant at all soil depths in the dry season of JJA. The overall results show that soil moisture content over Uganda is drying out.