As a large groundwater basin, the Northern Kalahari Aquifer (NKA) system is a major regional water resource with important impacts on the sustainability of ecosystems services and water supply in Southern Africa. The Angola High Plateau (AHP) is a critical recharge area of the NKA, and despite its central role in the distribution of regional freshwater resources, the water budgets of basins with headwaters on the AHP have not been studied previously. Here, we focus on the Upper Zambezi River Basin (UZRB). Specifically, a distributed coupled surface-groundwater model is used to characterize the seasonal (wet/dry season) and inter-annual variability of the water budget of the UZRB over a ten year period (2001-2010). The model is implemented at 5 km resolution. Atmospheric forcing datasets including air temperature, air pressure, wind velocity, specific humidity, and downward radiation were extracted from ERA-Interim (3-hourly, about 80km), higher resolution analysis data, and TRMM rainfall products were downscaled to the model resolution. Leaf Area Index (LAI) and albedo were generated from MODIS MOD15A2 and MCD43B3 products, respectively. Soil texture in the UZRB was extracted from the Harmonized World Soil Database (HWSD), and soil parameters were derived according to the soil textures. Inter-annual variability is controlled by the relative positions of the Inter-Tropical Convergence Zone (ITCZ) and the Congo Air Boundary (CAB), which determine the frequency and nature of weather systems propagating over the AHP. The 10 year simulation shows that inter-annual hydrometeorological variability has a strong impact in water storage in the NKA due to vigorous surface-groundwater interactions in the AHP, and in the UZRB in particular. Model results will be compared against monthly water storage anomalies from the GRACE Terrestrial Water Storage (TWS) data similar to Rodell et al. (2009).

Rodell, M., Velicogna, I., Famiglietti, J.S., 2009. Satellite-based estimates of groundwater depletion in India. Nature, 460(7258): 999-U80.