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Climatic variability over southern Africa is a well-recognized phenomenon, yet knowledge about the temporal variability of extreme seasons is lacking. This study investigates the intraseasonal progression of extreme seasons over Zimbabwe using precipitation and normalized difference vegetation index (NDVI) data covering the 1981–2005 period. Results show that the greatest deficits/surpluses of precipitation occur during the middle of the rainfall season (January and February), and the temporal distribution of precipitation during extreme dry seasons seems to shift earlier than that of extreme wet seasons. Furthermore, anomalous wet (dry) conditions were observed prior to the development of extreme dry (wet) seasons. Impacts of precipitation variations on vegetation lag by approximately 1–2 months. The semiarid southern region experiences more variability of vegetation cover than do the northern and eastern regions. Three distinct temporal patterns of dry years were noted by considering the maximum NDVI level, the mid-postseason NDVI condition, and nested dry spells. The findings of this study emphasize that climate extremes ought not to be simply understood in terms of total seasonal precipitation, because they may have within them some nested distribution patterns that may have a strong influence on primary production.

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.

Abstract:Understanding the patterns of human concentrations within megacities is of fundamental importance to our understanding of megacity dynamics, and for megacity management and policy making. This study presents an updated investigation of the historical expansion of densely inhabited districts (DIDs) in the world's largest megacity, Tokyo. Long-term DID data (1960-2010 at 5-year intervals were analyzed in a geographic information systems framework.Results show that Tokyo completed rapid growth phase and is now in a maturity phase with minimal growth. Extension was the main form of expansion, although fragmented growth in the form of patches was also noted. The rate of DID expansion was strongly related to economic trends. However the direction and shape of expansion was influenced much by geographic and policy related factors. West and southern directions had earlier and greater expansion, likely related to the historical Tōkaidō corridor. Over 95% of all DIDs are located within 4km distance from a railway line. The coastline and distance from the CBD had some modifying influence. During the course of expansion, there was substantial decrease of population density in the inner wards. Future trends in Tokyo's DIDs will be greatly influenced by aging demographic trends. This study therefore shows that megacity spatial expansion is a dynamic process influenced by various processes whose roles vary over time.