How climate variations are reflected in root zone storage capacities

Changes in climatic conditions and vegetation cover are expected to affect the hydrological behaviour of catchments. An important variable in hydrological models trying to catch this behaviour is the catchment representative root zone storage capacity (S-r). Traditionally, S-r is derived from soil properties, which makes it difficult to incorporate changes in climatic and vegetation conditions. Using climate data rather than soil data to derive S e enables the evaluation of the effect of climate variability on modelled runoff through S-r-estimates. A temporal variability in S-r reflects a changing root system and thus the vegetation's adaptation to medium-term fluctuations in the climate. The sensitivity of the derived S e to variations in climate could give information about the impact of climatic changes on the hydrological behaviour of a catchment. Therefore, this study investigates how a climate-derived root zone storage capacity changes under changing climatic conditions. Southern Africa is selected as a study area, as this region represents a wide variety in climatic conditions, including very dry ones. S-r -values estimated for the current climate and vegetation cover are compared with S-r -values estimated for two cases with varying climatic conditions. The results show that these changes not only affect the root zone storage capacity, but differences in changing patterns are observed between grid cells as well. Especially, the current runoff coefficient and the inter-annual variability in precipitation and evaporation appear to be important variables in determining the change behaviour of S-r.