Combined snow and streamflow modelling to estimate impacts of climate change on water resources in the Clutha River, New Zealand.

Global climate is changing in response to increased greenhouse gas concentrations in the atmosphere. This change may have multiple hydrological effects. The most obvious effect of climate change on hydrology is through changes in rainfall patterns, but hydrology is also strongly affected by changing temperatures (e.g., changes in evapotranspiration and snowfall). In this paper we focus on the effects of climate change on the Clutha River, in the South Island of New Zealand. We present an analysis of the projected weekly averaged flows of the Clutha at Balclutha, comparing the current situation (1980-1999) with two future time periods (2030-2049 and 2080-2099) for one \"middle of the road\" emission scenario, A1B, using data from the IPCC Fourth Assessment Report. The investigation used the distributed hydrological model TopNet, which includes a snow model. The model was validated against 20-year streamflow records for three locations in the catchment. Climate predictions of 12 different Global Circulation Models for the A1B scenario (as well as the average of those 12) were used as input to the model. In the future scenarios annual precipitation increases in this catchment. The total yearly streamflow increases as a response (∼6% for 2040 scenario and ∼10% for 2090 scenario); however the relative contribution of snowmelt to streamflow decreases. The most striking change is in the seasonality of streamflow. Streamflow in winter and spring increases substantially, whereas stream-flow in summer and autumn is relatively unchanged. Two factors contribute to this effect: 1) total precipitation increases over winter and spring (up to 40% in some areas of the catchment for the 2090 scenario), whereas it remains constant or decreases slightly over summer and autumn in some areas, and 2) during winter and spring, precipitation falls more often as rainfall (rather than snow) in the future scenarios. [ABSTRACT FROM AUTHOR]