Analysing changes in water availability to assess environmental water requirements in the Rivirivi River basin, Southern Malawi

The headwater catchments of the Rivirivi River basin in Malawi play a vital role in meeting downstream water requirements. In recent years, the Rivirivi River flow regime has experienced changes in its hydrological regime, including an increased number of zero-flow days. This study was aimed at investigating some of the causes of these changes. Water quantity indicators were assessed through flow duration analysis of the river flow regime behavior before and after the introduction of the traditional water allocation practices and dam construction. Further, a desktop reserve model was applied to estimate the environmental water requirements. Anthropogenic land use induced change patterns were investigated by time series analysis of satellite imagery and their potential effect on water resources were inferred. The results indicate that there was a considerable difference in average annual stream flow between two identified main periods (between 1963-1983 and 1984-2004) and zero flows increased from 5% to 12%. In addition, the area experienced a 65% reduction in forest cover from 1992 to 2008 which resulted in increased high flow index by 16%. Furthermore, the ecosystems need approximately the range of 35-40% of the MAR to be maintained at Class A and the range of 9-13% of MAR for class D. The results suggest that anthropogenic activities have negatively affected low flow environmental flows requirements by increasing zero flow days in Rivirivi River catchment. However, total water usage remains below the river's MAR and the river can meet all water needs with proper management of the river flow regime.