The effects of climate change on runoff in the Lindis and Matukituki catchments, Otago, New Zealand

摘要

Climate change linked to anthropogenic emission of greenhouse gases is projected to have substantial effects on Earth's water resources. Changes in the amount and timing of runoff are environmentally, socially and economically important. While many studies worldwide focus on the hydrological effects of projected climate change, there have been few such studies in the Otago region of New Zealand, an important region for hydropower and agriculture. This investigation examines the effects of projected climate change on runoff in Otago, focusing on two tributaries of the Clutha River: the Lindis and the Matukituki. Runoff in these two catchments was modelled using the semi-distributed hydrological model TopNet. This hydrological model uses projections from 12 different General Circulation Models (GCMs), based on the moderate A1B emissions scenario, for two future time periods: 2030-2049, and 2080-2099. For each time period, projected monthly runoff totals were produced for each catchment. GCM ensemble mean annual runoff increased in both catchments in both future time periods: by 20.4% for the Lindis for the 2080-2099 period and by 12.8% for the Matukituki. All 12 GCM ensemble members show increasing annual runoff for the Lindis in the 2080-2099 scenario (ranging from 6.4 to 37.5%), with just one ensemble member showing a decrease for the Matukituki (range: -4.0 to +26.7%). Uncertainty between GCMs is greater for mean monthly runoff, with no clear signal either side of the baseline in a number of months. However, all GCMs indicate large increases in July-August runoff, which has the effect of amplifying the seasonal cycle of runoff for the Lindis while reducing it for the Matukituki. These changes in seasonality are consistent with projected increases in winter precipitation, as well as a larger proportion of this precipitation falling as rain rather than snow.