资源环境科技发展态势分析平台

This study investigates the temporal evolution of extreme rainfall seasons over Botswana, and their relationships to the growing season cycle of natural vegetation. Ground-based precipitation data and remotely sensed Advanced Very High Resolution Radiometer (AVHRR)-normalized difference vegetation index (NDVI) data are analysed for the July 1981-June 2006 period. Results confirm that Botswana's annual cycle of precipitation is characterized by substantial intra-seasonal variation, which is resonated in natural vegetation cover. During extreme wet (dry) years, the most extreme surpluses (shortfalls) of monthly rainfall were observed in the middle of the rainfall season (January-February). While rainfall receipts during season onset and cessation may not be the highest, they were found to have strong influence on NDVI coefficient of variation. Extreme wet seasons could be distinguished from moderate wet seasons by examining their monthly peak patterns. Furthermore, the November-December period was identified through the NDVI as the critical period when extreme conditions may begin to emerge. These findings could have important implications for supporting seasonal forecasts and optimizing rainfed agricultural adaptation and natural resources management in southern Africa.