The potential impact of climate change on seasonal snow in New Zealand: Part I - An analysis using 12 GCMs

Seasonal snow directly affects New Zealand’s economy through the energy, agriculture and tourism sectors. In New Zealand, little is known about the long-term variability of the snow cover and the expected impacts of climate change on snow cover. The lack of systematic historical snow observations in New Zealand means that information on interannual variability, trends and projections of future seasonal snow must be generated using simulation models. We use a temperature index snow model to calculate the accumulation and ablation of the current (1980-1999) snowpack for more than 37,000 third-order river basins with 100 m contour intervals, resulting in over 200,000 individual model elements in New Zealand. Using this model, which captures the gross features of snow under the current climate, we assess the range of likely effects of climate change on seasonal snow in New Zealand using downscaled temperature and precipitation changes from the middle of the road (A1B) climate change projections from 12 general circulation models (GCMs). For each of the 12 GCMs, we consider two future time periods 2030-2049 (mid-point reference 2040) and 2080-2099 (mid-point reference 2090). These future time periods are compared to simulations of current, 1980-1999 (mid-point reference 1990), seasonal snow. Our results show that on average at a national scale, at nearly all elevations, the 2040s and 2090s result in a decrease in snow as described by all of our summary statistics: snow duration, percentage of precipitation that is snow and peak snow accumulation in each year. This decrease in snow is more marked at elevations below 1,000 m but is evident at all but the very highest elevations. Relative to snow simulations for average peak snow accumulation for the present, we observe that by the 2040s, depending on the GCM used, there is a reduction of between 3 and 44 % at 1,000 m, and an increase of 8 % through to a reduction of 22 % at 2,000 m. By the 2090s, the average reduction is greater, with a decrease of between 32 and 79 % at 1,000 m and between 6 and 51 % at 2,000 m. More substantial reductions are observed below these elevations. When we consider the elevation where snow duration exceeds 3 months, we see a rise in this elevation from 1,550 m in the 1990s to between 1,550 and 1,750 m by the 2040s and 1,700 and 2,000 m by the 2090s, depending on the GCM used. The results of this work are consistent with our understanding of snow processes in general and with work from other similar mid-latitude locations.