Hydrological response to land use change and climate variability and its effects on households’ water availability in the sig catchment, Tanzania

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University of Dar es Salaam
Overtime, hydrological systems of the Sigi catchment have indicated changes with unknown forms and magnitudes. These changes have profound effects on households that depend on increasingly fragile hydrological resources for their living. To uncover the dynamics in the hydrological systems, this study established the patterns ad trends of land use change and climate variability which were linked to hydrological response and ascertain their effects on households’ water vulnerability. The regression model, Mann-Kendall trend test, and Sen’s slope estimator were run to depict significance, trends, direction and magnitude of climate variability. The supervised classification using post-classification comparison, change detection, and transformation matrices were performed to ascertain spatial and temporal change in land use. The soil and water assessment tool (SWAT) was used to simulate hydrological response to the separate and combined effects of land use change and climate variability. Statistics analysis of 344 household questionnaires was done using descriptive and inferential statistics to understand extent of water availability. Finally, the structural content analysis was used to analyze the result from in-depth interviews and participatory field observations. Findings on the climate variability showed a shift from wet conditions in 1960s to relatively dry conditions in 2010s. Annual rainfall indicated a decrease of 3.2 mm-yr-1, while consecutive wet days and daily maximum rainfall decrease at a rate of 0.05 days-yr-1 and 0.06 mm-yr-1, respectively. The result showed increasing trends of consecutive dry days (0.16 days-yr-1) and simple daily intensity (0.06 days-yr-1), though the increase was not statistically significant (ρ>0.05). Additionally, trends of temperature in the upper and lower catchment increased by 0.02oC-yr-1and 0.01oC-yr-1, respectively. Land use change showed reduction in closed forests, shrub lands, and water bodies while open forests, built-up lands, and cultivated lands showed increasing trend. SWAT simulation showed good performance with Nash-Sutcliff Efficiency (NSE) =0.58 and coefficient of determination (R2) =0.67 for calibration, and NSE=0.56 and R2=0.64 for validation period. Hydrological to land use change indicated increase by 23.1 mm and 7.2 mm, respectively. Influence of climate variability increased surface runoff by 29.9 mm, while base flow and water yield decreased by 36.1 mm and 14.2 mm, respectively. the observed hydrological change have affected households’ water availability since nearby one-third of the households (36.9% had to travel up to 2.5 km to water supply sources. From the study it has come out clearly that rainfall, temperature, and land use have significantly changed. It is also apparent to mention that the impacts of climate variability on hydrology of the Sigi catchment are larger than those of land use change. Although the Sigi catchment has various water supply sources, their number over time. Owning to the dilemma facing water resources in this era of climate variability and use change, long-term planning that balance households’ livelihood options that offers economic well-being and water resources management option is needed.
Available in print form, Eat Africana Collection, Dr. Wilbert Chagula Library,(THS EAF QC902.T34C446)
Climate change, Land use, Climate variation, Sigi cathment
Clement, M. (2019) Hydrological response to land use change and climate variability and its effects on households’ water availability in the sig catchment, Tanzania. Doctorial dissertation, University of Dar es Salaam, Dar es Salaam.