11.7.3.3 Snow Cover

The likelihood that precipitation will fall as snow will decrease as temperature rises. Hennessy et al. (2003) modelled snowfall and snow cover in the Australian Alps under the CSIRO (2001) projected temperature and precipitation changes and obtained very marked reductions in snow. The total alpine area with at least 30 days of snow cover decreases 14 to 54% by 2020, and 30 to 93% by 2050. Because of projected increased winter precipitation over the southern Alps, it is less clear that mountain snow will be reduced in New Zealand (Ministry for the Environment, 2004; see also Box 11.3). However, marked decreases in average snow water over New Zealand (60% by 2040 under the A1B scenario) have been simulated by Ghan and Shippert (2006) using a high-resolution sub-grid scale orography in a global model that simulates little change in precipitation.

11.7.3.4 Potential Evaporation

Using the method of Walsh et al. (1999), changes in potential evaporation in the Australian region have been calculated for a range of enhanced greenhouse climate model simulations (Whetton et al., 2002; Cai et al., 2003b; McInnes et al., 2003, 2004; Hennessy et al., 2004a,b). In all cases, increases in potential evaporation were simulated, and in almost all cases, the moisture balance deficit became larger. This has provided a strong indication of the Australian environment becoming drier under enhanced greenhouse conditions.