Effects of rising water tables and predicted climate changes on annual and monthly flood frequencies

Sivandran, G.; Sivapalan, M.

American Geophysical Union – EUG Joint Assembly, Nice, France, 2003, abstract #7981

Rising water tables in the Blackwood catchment in the south-west of Western Australia have been attributed to the extensive landuse change that has occurred in the region over the past 50 years. The effects of this landuse change, coupled with predicted climate changes for the region, could have a pronounced effect upon the future flood frequency behaviour of the catchment. A continuous Monte Carlo simulation model for the Blackwood catchment was constructed to mimic the catchment’s response to potential changes in the climatic inputs and hydrological characteristics. This model consists of two components: 1) a stochastic rainfall generator that mimics both the low frequency summer tropical systems and the seasonal winter frontal systems; 2) a simple rainfall-runoff model that simulates saturation excess runoff, infiltration excess runoff and subsurface stormflow, and can adequately represent the effects of rising water tables. The Monte Carlo model was then utilised to generate multiple climate change and landuse scenarios to explore the sensitivity of such changes on the flood frequencies of the Blackwood catchment. Landuse results in rising water tables and therefore greater peak flows in winter, however a more significant effect of landuse is the effect clearing has upon summer runoff characteristics due to its influence on infiltration excess runoff. This together with climate change projections of increases in the frequency of extreme summer rainfall events has the potential to increase the frequency and magnitude of extreme summer floods.