Grey Theory Approach to Quantifying the Risks Associated with General Circulation Models

Assessing the risk to water resources facilities under climate change is difficult because the uncertainty associated with 2xCO2 climate scenarios cannot be readily quantified. Grey systems theory is used to develop a grey prediction model (GPM) that provides an interval of uncertainty. The GPM is used to extrapolate a numerical interval around the decadal averages of precipitation and temperature through the year 2010 for a site in Northwestern Canada. The extrapolation is calibrated on 20 years of data and validated against observations for the 1980’s. The values in the 1990’s correspond to observed trends in the area. The temperature and precipitation values are used to develop a grey water balance model. The grey intervals for annual potential evapotransipiration, deficit and surplus are used to evaluate the reliability of a transient and three equilibrium climate change scenarios scenarios. The grey intervals are not coincident with the transient output, but they are trending towards the equilibrium scenario values. This suggests that this particular transient scenario is inadequate for risk assessment, and although the equilibrium scenarios appear to be within the grey interval, they represent years beyond a reliable GPM extrapolation.