Aridity changes and its association with drought severity in Botswana

Global warming is likely to increase climatic variability especially in semi arid areas. The variability is expected to be registered through changes in rainfall patterns and temperature trends, thus through changes in aridity and drought severities. This makes it necessary to periodically monitor these climatic variables by examining trends in aridity and their association with drought severity. This study investigated trends in aridity using Mann-Kendall (MK) trend analysis and their association with drought severity using aridity indices (AI) and standardized precipitation evaporation indices (SPEI). This was achieved by using climatic information observed from 1960-2014 at 14 synoptic stations across Botswana. Results from seasonal aridity revealed that there was marginally increased aridity in 71% of the stations at the end of the summer rainfall (wet period) and in 64% of the stations at the end of the dry winter period. Marginally increasing trends for annual aridity was also observed in 64% of the stations at the end of December. Interestingly the trends in both seasonal and annual aridity were generally not found to be statistically significant except at Kasane. However, significant positive correlations between AI and SPEI were found except at Maun. The study concludes that though the association between drought severity and aridity index are significant albeit with insignificant changes in aridity indices, the drought severities in Botswana could be from short term droughts.