Critique of Drought Models in the Australian Drought Exceptional Circumstances Report (decr)

This paper1 evaluates the reliability of modeling in the Drought Exceptional Circumstances Report (DECR) where global circulation (or climate) simulations were used to forecast future extremes of temperatures, rainfall and soil moisture. The DECR provided the Australian government with an assessment of the likely future change in the extent and frequency of drought resulting from anthropogenic global warming. Three specific and different statistical techniques show that the simulation of the occurrence of extreme high temperatures last century was adequate, but the simulation of the occurrence of extreme low rainfall was unacceptably poor. In particular, the simulations indicate that the measure of hydrological drought increased significantly last century, while the observations indicate a significant decrease. The main conclusion and purpose of the paper is to provide a case study showing the need for more rigorous and explicit validation of climate models if they are to advise government policy.