Characteristics of Past and Future Drought Events in South Sudan

Abstract

Extreme meteorological events, negatively affect economic sectors and the natural environment as well as human society. These meteorological extremes include floods, tropical cyclones, heat waves, and droughts. Investigating drought characteristics in South Sudan is very important to understand its behavior and pattern. The primary aim of this study is to investigate past and future droughts in South Sudan. The data used in this study is the Climate Hazards Group Infrared Precipitation with Station data (CHIRPs v2.0) from 1981-2022 with a horizontal resolution of 0.05°. The historical CMIP6 dataset from 1981 – 2014 and the future period of 2030 – 2100, with 2030 – 2065 as near and 2066 -2100 as the far future (end century) was also used to project future characteristics of drought in South Sudan. This period was divided into two equal short periods to define near and far future periods of the study. The SPI was calculated for two seasons of MAM and JJAS to identify past drought years (1981-2022). The SPI has demonstrated the ability to capture past drought events in both MAM and JJAS seasons over South Sudan. The Mann Kendall’s test at a significance level of 95% was carried out on the JJAS and MAM rainfall amounts for four representative zones (1981-2022). This test was done to determine rainfall trends in South Sudan. Simulated CMIP6 rainfall data was compared with the observed rainfall data (CHIRPs v2.0) for the period 1981 – 2014 to evaluate the CMIP6 model’s performance over South Sudan using correlation coefficient, RMSE, and bias metrics on a seasonal basis, both the JJAS and MAM. The CMIP6 historical data from the selected GCMs and SSP126, SSP245, and SSP585 as climate change scenarios were used for the projection of drought. Evaluation of the seasonal correlation, bias, and RMSE indicated that all 4 models have better performance during the MAM season and underperform in replicating the JJAS season over South Sudan. This is because the models overestimate the MAM season and underestimate the JJAS season. The ensemble means of the models was used over individual models to project drought over South Sudan. The projected drought events in South Sudan indicated that moderate drought patterns are expected in Juba, Raja, and Wau in both the near and far future. The occurrence of moderate droughts in these areas may be attributed to the increase in temperature in South Sudan, which is linked to climate change. Renk reported near-normal conditions in both the near and far future in both the MAM and JJAS seasons. In general, there will be a decrease in drought frequency and intensity in South Sudan in the future. The analysis of drought was based on the four classes of drought (near normal, moderate, severe, and extreme droughts). The decrease in drought frequency and intensity in all the stations in both seasons is linked to future changes in precipitation. All these changes may be attributed to global warming that is caused by the climate change effects. The results obtained from this study will be used by climate information users to prepare for the expected changes in the future. The information can also be used as the basis for drought studies and projections in South Sudan.