Hydrological sentinels and the relative emergence of climate change signals in New Zealand river flows

Abstract

Hydrological impacts of climate change are prompting water resource and flood hazard management to adapt to non-stationary conditions. Among the factors influencing these policy decisions is the question of timing: when are we likely to see climate change effects? Using a national climate-hydrology model cascade over the 21st century, times and extents of emergence of six hydrological metrics are evaluated across New Zealand rivers. While the stringency of the emergence criteria has a significant effect on timing and extent, emergence for all metrics generally occurs after mid-century, if at all, and in the country’s South Island. Looking at the first emerging metrics, in contrast, allows us to sidestep the high uncertainties of the time of emergence, revealing mean winter flows to be the most extensive sentinel of climate change in New Zealand rivers among the metrics considered. This has implications for hydrological monitoring to inform timely climate change adaptation.