The effects of climate and changing land use on the discharge regime of a small catchment in Tanzania

Increasing pressure on water resources makes it necessary to understand the reasons for the changes in the run-off characteristic of the Ngerengere River in Tanzania during recent years. Changing land use and changes in climate boundaries are identified as effects. A combination of statistical analysis and the use of the hydrological model SWAT were chosen to handle the problem of poor data quantity and quality with non-overlapping periods. Changes in the discharge regime were identified with the 5th percentile of the flow duration curve as an indicator for high-flow events, with an indicator for low-flow duration and with the base flow index. The analysis showed that climate boundaries and changing land use do not have a uniform effect on discharge in the catchment. Changing land use affects surface run-off and increases floods in the mountainous areas. Changes in climate boundaries increase the duration of low flow and no flow in the Ngerengere catchment. Changes in climate conditions and land use had antipodal effects on parts of the discharge regime. Thus, the observed changes in land use and climate conditions partially compensate for each other.