Gaughan, AE; Stevens, FR; Gibbes, C; Southworth, J; Binford, MW (2012). Linking vegetation response to seasonal precipitation in the Okavango-Kwando-Zambezi catchment of southern Africa. INTERNATIONAL JOURNAL OF REMOTE SENSING, 33(21), 6783-6804.
Understanding how intra-annual precipitation variability affects seasonal vegetation dynamics is critical for assessing the potential impacts of climate variability on vegetation structure and composition. This is important in semi-arid and arid ecosystems of southern Africa, where water is a limiting resource and timing of seasonal rainfall combined with the water storage capacity of different plant vegetation types affects remotely measured phenological cycles. Various lags and leads of savanna vegetation response to rainfall have been identified using remotely sensed data, but little attention has been given to vegetation greenness leading into the dry season. Vegetation production at the onset of the dry season interacts with the availability of water resources affecting fire dynamics, forage materials for wildlife and wildlife movement throughout the dry season. This is important for southern Africa as large proportions of the human population and economy are dependent on wildlife tourism. This study investigates the response of the end of the wet season vegetation production, as measured by Moderate Resolution Imaging Spectroradiometer (MODIS) normalized difference vegetation index (NDVI) greenness, to the different months of wet season rainfall for different savanna vegetation types in a regional catchment of southern Africa. We estimated monthly precipitation using Tropical Rainfall Monitoring Mission 3B43 data and used MODIS 13A1 NDVI at a monthly time step for the years 2000-2009. Our model estimated greenness at the beginning of the dry season from the prior rainy season (October-April) precipitation using geographically weighted regression (GWR). The results show intra-annual wet season rainfall accounts for significant amounts of April NDVI variation. Overall intra-annual rainfall has a stronger effect for areas with greater proportions of grassland and dry, deciduous woodlands than for wetter, evergreen woodlands. These findings support previous research by highlighting the stronger association of grassland and open canopy woodlands to the end of the wet season monthly rainfall. This relationship is important for understanding seasonal precipitation effects on different savanna vegetation covers.