Impact of Climate Variability and Change on Sorghum Yield in Lesotho

Abstract

Climate variability characterized with hazardous extreme weather events is a major threat to rain-fed agriculture production in Lesotho resulting into increased food insecurity and poverty in the country. Therefore, this research sought to evaluate the impact of climate variability and change on sorghum yields in Lesotho. The data used in this study comprise observed rainfall and maximum temperature as well as minimum temperature datasets for Thaba-Tseka, Butha-Buthe, Leribe and Mohale’s Hoek from 1986-2018 obtained from the Lesotho Meteorological Service, and sorghum yield data from 1999/00 to 2017/18 obtained from the Lesotho Bureau of Statistics. Other data sets included historical and projected rainfall and temperature datasets from 1986-2005 and 2030-2060 respectively obtained from the Climate System Analysis Group (CSAG). The variability and trends on sorghum yield, seasonal rainfall and temperature datasets were analyzed using the coefficient of variation and Mann-Kendall statistical test respectively. Rainfall distribution was analyzed using the Precipitation Concentration Index. The relationship between sorghum yield and climate parameters was established by, first, determining the degree of association between climatic elements and sorghum yields using correlation analysis, and linking the pairs of variables that gave rise to statistical significant correlations using regression analysis. The significance of correlation was determined using student t-test. The impact of climate change on sorghum yield was analyzed using the AquaCrop model and data from suitable CMIP5 GCMs under RCP 4.5 climate scenario. CMIP 5 GCMs performance was assessed using correlation and Root Mean Square error methods. The results showed moderate rainfall variability, with uniform to moderate precipitation concentration index (PCI<16) in all the study areas. Both seasonal maximum and minimum temperature revealed less variability. Non-significant increasing trends (=0.05) were depicted for rainfall in all the areas under study. Statistically significant increasing trends were depicted for minimum temperature in all the four stations whereas maximum temperature showed significant increasing trends in Thaba-Tseka and Mohale’s Hoek. However, the trends were not significant at Leribe and Butha-Buthe. Sorghum yields exhibited high variability (CV>30%) in all the study areas, with non-significant decreasing sorghum yield trends (=0.05) at Thaba- vi Tseka, Leribe and Butha-Buthe and an insignificant increasing trend for sorghum yields in Mohale’s Hoek. Statistically significant positive correlation coefficients was depicted between rainfall and sorghum yields in Leribe, Mohale’s Hoek, Butha-Buthe and Thaba-Tseka. Both maximum and minimum temperature showed positive but insignificant correlation coefficients with sorghum yields, except in Butha-Buthe and Leribe where maximum temperature indicated a significant positive correlation with sorghum yields. The study depicts a statistically significant relationship with rainfall, maximum temperature and sorghum yield (p<0.05) in Butha-Buthe but in Leribe, Thaba-Tseka and Mohale’s Hoek only rainfall and sorghum yields showed significant relationships. The ensemble, CNRM-CM5, FGOALS-s2 and GFDL-ESM2M GCM’s performed relatively well in simulating temperature and rainfall in the study area, and were therefore used for projecting future climate (2030/31-2059/60) during the cropping seasons. All the models indicated uncertainty in projecting future rainfall. The ensemble revealed increasing rainfall in Butha-Buthe, Leribe and Mohale’s Hoek and a decline in rainfall in Thaba-Tseka. A rising temperature was projected in all the study regions during the 2030/30 to 2059/60. The output from Aquacrop model driven by the GCMs ensemble projected increasing sorghum yields in Leribe and Butha-Buthe and a decline in sorghum yield in Thaba-Tseka and Mohale’s Hoek during 2030/31 to 2059/60 cropping season. Climate change therefore presents both positive and negative impacts on sorghum production in Lesotho. This calls for integration of climate change response measures into agricultural policies and strategies to support farmers to adapt to the changing climate impacts in order to increase and sustain sorghum productivity and nutrition security under changing climate.