THE INFLUENCE OF SOIL TYPE ON THE RELATIONSHIPS BETWEEN NDVI, RAINFALL, AND SOIL-MOISTURE IN SEMIARID BOTSWANA .2. NDVI RESPONSE TO SOIL-MOISTURE

This article is the continuation of a study of the relationship between NDVI and rainfall in semiarid Botswana. That study notes significant differences in the NDVI-rainfall relationship for various soil types and a much higher ratio of NDVI to rainfall over Botswana than over comparable regions of the Sahel or East Africa. The current article examines the extent to which differences in the rate of sell moisture generation, as a function of soil type or locality, can account for these results. It concludes that they cannot. This study demonstrates that the five soil types do differ significantly with respect to both the rate of soil moisture generation per unit rainfall and the ratio of NDVI to soil moisture. The most productive soils are the clay-rich vertisols; the arenosols are the feast productive, although the rate of soil moisture generation is about the same for both soil types. The results also suggest that over Botswana NDVI may be significantly influenced by soil reflectivity and that the vegetation growth is promoted by exogenous soil water originating as runoff in the surrounding higher terrain.