To investigate the impact of regional climate change on surface and subsurface hydrology in the Volta Basin, a joint climate-hydrology model was developed. A mesoscale meteorological model (MM5) was downscaled dynamically from ECHAM4 outputs (scenario: IS92a) to a resolution of 9km for two 10-year time-slices, 1991-2000 and 2030-2039. The downscaled outputs were coupled one-way to the physically-based, distributed hydrological model, WaSiM, using a spatial resolution of 1 km.
The analysis of this joint climate-hydrology modeling approach shows a very heterogeneous response of river runoff to changes in climate variables. A small increase in annual rainfall was observed which lead to an increase in discharge. Nevertheless, most of the rainfall surplus was found to evaporate due to an increase in temperature and consequently in potential evaporation.
At the beginning of the rainy season, a significant decrease in rainfall was found in connection with a delay in the onset of the rainy season, but it did not have strong impacts on runoff. The largest percentage change was observed for infiltration excess (direct runoff), but the impact was strongly dependent on actual and past rainfall intensities, soil moisture and evapotranspiration.
As a central topic, the climate change signal for several variables was examined with respect to simulated interannual variability via the signal-to-noise ratio. To determine whether the modeled signal is a clear sign of simulated climate change, or if they lie within the range of the regions' interannual variability, the signal-to-noise ratio of several variables was examined with respect to simulated interannual variability. Results indicate that there are only small changes in the runoff regime of the Volta between the two simulated time-slices, and that the changes are predominantly within the range of the interannual variability.
See here the results of Climate Change research for the Volta Basin Area.