Spatial and temporal variability of precipitation in the Okavango-Kwando-Zambezi catchment, southern Africa

This paper examines long-term environmental variability across the Okavango-Kwando-Zambezi catchment area through the descriptive spatio-temporal analysis of rainfall change in this semi-arid dryland region of southern Africa. Recent multi-decadal trends indicate declining mean annual precipitation, increasing variability, and an increased significance of warm phase ENSO events in the region. It has been suggested that the change in the precipitation pattern coincide with a shift in the global coupled ocean-atmosphere system during the late 1970s. We investigate the inter-annual variability of regional precipitation dynamics within three catchments (Okavango, Kwando, and Zambezi – the OKZ catchment) in southern Africa from 1950-2005. Situated in the Kavango-Zambezi Transboundary Conservation Area (KAZA), the study area (693,000 km2) provides a vital corridor for wildlife migration along which precipitation inputs constitute an important water source in an otherwise water-limited ecosystem. Precipitation patterns are investigated using modeled precipitation (0.5o x 0.5o grid cell resolution) that provides a complete, historical dataset. At the regional scale, raster surface images are created using an inverse distance weighted (IDW) spatial interpolation technique which allows for identification and comparison of annual precipitation changes across the study area. Water flowing into the KAZA from upstream areas of the three basins can ameliorate the effects of local meteorological drought or exacerbate local flooding. Annual precipitation totals to each individual basin are estimated from the modeled precipitation dataset and changes in the frequency of occurrences of wet, dry, or normal years (terciles) before and after the postulated shift in global climate are examined using the hypergeometric distribution . Any changing correspondence of El Niño Southern Oscillation (ENSO) events to extremes are also investigated in a similar fashion. Results indicate decreasing precipitation patterns and increased association of dry years and warm phases of ENSO across all three sub-catchments following the 1970s. Knowledge of the historical spatio-temporal shifts in precipitation distributions plays a direct role in decisions made on the ground regarding agriculture, wildlife, and resource management. An explanation of inter-annual precipitation patterns provides important information for local collaboration between national parks and communities for decisions concerning water access and usage between wildlife and humans.