Analysis of Spatio-temporal rainfall trends and rainfall variability in Botswana between 1958 and 2019

Abstract

Environments with a climatic characteristic of semi-aridity exhibit high rainfall variability, increasing significantly as the climate changes. In this study, rainfall concentration and Spatio-temporal trends in annual and seasonal (November to March) rainfall in Botswana were analyzed. The satellite data (1958-2019) is obtained from the Southern African Science Service Centre for Climate Change and Adaptive Land Management and the Climate Toolbox. The Mann–Kendall trend test (MK), autocorrelation function (ACF), relative percentage change (RPC), precipitation concentration index (PCI), and Theil–Sen's slope estimator (β) methods were adopted for data analysis. The regions include Gaborone, Maun, Francistown, Serowe, Kasane, Tsabong, Ghanzi, and Pandamatenga. The results indicated that the magnitude of change of change of the significant downward trends in the annual rainfall was found to be -1.11 mm/year at Maun, -1.62 mm/year at Ghanzi, -0.33 mm/year at Pandamatenga, and -0.25 mm/year at Tsabong. The magnitude of change of change of the significant downward trends in the seasonal rainfall was between -0.60 mm/year at Pandamatenga and -0.19 mm/year at Tsabong. All these regions, except Ghanzi, experienced a downward trend in the rainfall distribution. This is owing to the synoptic characteristic of the below-average geopotential heights over Ghanzi. Which might exacerbate the formation of convective systems, leading to a positive rainfall trend at Ghanzi. The annual calculated PCI values are divided into three classes; PCI>10≤15, PCI>16≤20, and PCI>20. The Mann-Kendall analysis of the PCI values indicates that all the regions experienced a downward rainfall trend, implying that it is heading toward a uniform to a moderate distribution. There were distinct patterns that emerged from the Pandamatenga region, indicating a strongly irregular distribution. The regions of Kasane, Maun and Francistown, demonstrated moderate to an irregular distribution. For Gaborone and Francistown, results showed occurrences of a moderate to strongly irregular distribution.