Assessment of agricultural drought using long¬term simulated soil moisture in Simiyu River catchment

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University of Dar es Salaam
Earlier studies in Simiyu river catchment using physics based distributed hydrological model SWAT, suggested that rainfall was not catchment representative, hence attempt was made to interpolate rainfall using rainfall predictive variables of altitude and distance from Lake Victoria. The rainfall interpolation was also intended to acquire a long-term dry year which would be used in the assessment of agricultural drought using maize as a reference crop. Missing values prevented classification of rainfall years into dry. normal and wet years. Model efficiency criteria were reduced from annual to seasonal models; and as a result models for smaller time scales of monthly, weekly and daily models were not anticipated. SWAT was used to predict soil moisture based on rainfall-runoff transformation in which two outlets were used. Ndagalu outlet gave model efficiency criterion of 0.58 and 0.41 in calibration (1976/77) and validation periods (1980/81) respectively. Sayaga outlet gave model efficiency criterion of 0.01 and -0.48 in calibration (1973/74) and validation (1976/77) periods respectively; and as a result, Sayaga outlet was not used in the sequent assessment of agricultural drought due to poor agreement between observed and simulated hydrographs. Assessment of agricultural drought revealed only 3 out of 13 SWAT based sub-basins (of 40.5% by area) could marginally survive rainfed agriculture with maize as reference crop. The value of the study is that it can be extended for other crops using different input data in food security and management of water in agricultural sector. Furthermore, upon modifications it could also be used to compute spatial drought indices and may be used to draw estimated irrigation scheduling margins for different crops in other catchments.
Available in print form, East Africana Collection, Dr. Wilbert Chagula Library, Class mark (THS EAF S594.T34M34)
Soil moisture, Agricultural drought
Malembeka, F (2007) Assessment of agricultural drought using long¬term simulated soil moisture in Simiyu River catchment, Master dissertation, University of Dar es Salaam. Dar es Salaam.