Predicting hydrological droughts from a Standardized precipitation index (SPI) in South Phuthiatsana River basin, Lesotho

Abstract

Droughts affect Lesotho in varying degrees every year leading to shortage of water, posing a threat to nature, quality of life and economy. Although hydrological droughts are defined by below long-term mean of annual flow, the cause is mainly below normal precipitation falling on the catchment. Hydrological droughts characteristics analysis need streamflow data but most rivers in Lesotho are un-gauged and those which are gauged have been recently gauged which makes the data not long enough and unreliable for the analysis. However, reliable meteorological data is available in Lesotho which can be used for predicting hydrological droughts from precipitation so is the main objective of this study. This research is using Standardized Precipitation Index (SPI) at 3, 6, 12 and 24 months time scale to find the correlation of streamflow and SPI values which will result in identifying severity and duration of meteorological drought that causes the below normal streamflow in South Phuthiatsana River basin in Lesotho. The results showed that at 6- months SPI - severity of meteorological droughts- the streamflow can be reduced to below mean annual flow.