Spatial interpolation of extreme rainfall events over the past 50 years (1970 - 2019): a case study from central Southern Africa

Abstract

Droughts have been identified as recurring natural hazards in various parts of the world. The study region is in a semi-arid area and this area exhibits high climate variability, and the frequency of this variability has been increasing in recent years. The present study was conducted to analyse the spatiotemporal distribution of extreme rainfall events in the central region of southern Africa. Rainfall data used in this research was obtained from the Botswana Meteorological Office and the South African Weather Service. The analysis spans a period from 1970 to 2019. Climate data obtained from the two meteorological offices was analysed using three methods, Standardized Precipitation Index (SPI), Inverse Discrete Weighing (IDW) and Ordinary Kriging (OK). The interpolation methods used in this study were applied to spatially distributed precipitation data. Based on the results of the study, various drought occurrences have been identified at the weather stations. In the study region, normal drought conditions prevail, followed by moderately dry drought conditions. The El Niño years that coincide with droughts in the study region are 1963/1964, 1994/1995, 2002/2003, 2004/2005, 2006/2007, 2015/2016. As per SPI calculations, the years 1991 and 1992 had more than 10 weather stations experiencing dry drought conditions. The years 1999 and 2005 had the most weather stations recording the occurrence of wet drought conditions. The average precipitation of the area shows that the region is experiencing a decrease in precipitation at the rate of change of -2.42. This study has provided new insights into the occurrence of droughts and floods in central southern Africa and has further indicated there has been an increase in the frequency and intensity of droughts in this region over recent decades.