Modelling climate change effects on spatial variability in subcatchment flows in a mountain basin, New Zealand.

Abstract:

Climate change impacts on water resources can have significant spatial variability in heterogeneous mountain catchments. This study used the TopNet hydrological model to simulate existing and future streamflows under potential climate change in the Upper Waitaki River Basin, South Island, New Zealand. The basin includes unimpaired high-elevation catchments (Ahuriri), regulated glacier-fed catchments used for hydropower (Pukaki), and drier catchments in the Lower Waitaki (Hakataramea). Precipitation and temperature data for model input were based on the A2 emissions scenario and the average of 12 Global Circulation Models downscaled to the Virtual Climate Station Network (VCSN) database for the baseline (1980-1999), 2040s (2030-2049) and 2090s (2080-2099) periods. The percentage differences between 2040s and baseline median annual runoff range from 0-34%, 4-13% and 0-94%, and differences between 2090s and baseline are 0-70%, 10-30%, and 2-111% for the Pukaki, Ahuriri, and Hakataramea catchments, respectively. The spearman’s rank correlation coefficient showed correlations between median flows and elevation in the Pukaki (0.71) and Ahuriri (0.43) catchments (α = 0.05). However, correlation between median flows with slope and elevation were -0.37 and -0.68, respectively, in the Hakataramea catchment. There was also correlation between median flows with ice (0.84) and bedrock (0.51) in Pukaki subcatchments, and with ice (0.41) and bedrock (0.54) in Ahuriri subcatchments (α = 0.05). This study suggested greater spatial variability of climate change impacts on runoff in drier, lower-elevation catchments (Hakataramea) compared to wetter catchments at higher elevations (Pukaki and Ahuriri).