Gis base soil moisture accounting using global data The case of Pangani river basin, Tanzania

The Pangani basin is currently experienced water stress and resources conflicts brought on by competing water users. This study focused to assess the suitability of rain fed agriculture for various crops in Pangani river basin, by developing a GIS- based soil moisture budget model, which can predict soil moisture dynamics under different agricultural practices at basin to regional scale. Crop type, soil type and water holding capacity were integrated together through a soil water budget model to simulate a soil moisture regime if a particular crop had been grown. Analysis of these data was done for all the grids of 0.5*0.5 degrees. One crop was taken at a time and its moisture is analysed compared to standard crop water requirement given by FAO. The monthly global data of length between 10 to 60 years were used. In checking for uncertainly of input data, a comparison was made between global and ground/ measured data. The model output such as surplus/ gravity water was validated with measured surface runoff spatial. The findings shows that beans plants can be grown over the entire area except in most high hills. The maize plant can be grown from 80% to 90% of the area , and only a small area of about 20% is suitable for growing rice under rain fed agriculture. The main limitations during this study was the use of monthly data that does not yield enough surpluses to match observed river flows in some areas of the Pangani basin even with the assumption of zero overland flow and stream losses. The use of daily values is recommended over monthly values when feasible. This procedure should be extended to different parts of the country and maps should be established for different crops