Temporal and spatial emergence of climate change signals in New Zealand river flows

Abstract:

Impacts of climate change on the water cycle are increasingly prompting water resource and flood hazard management to account for non-stationary conditions. An important consideration in the transition is when and where stationary methods will no longer be sufficient. One approach for addressing this is to estimate the time and extent of sustained emergence of a climate change signal above background variability. Here, this is carried out for a suite of projected river flow metrics across New Zealand over the 21^st century using a national climate-hydrology model cascade. While the stringency of the emergence criteria has a significant effect on timing and extent, emergence generally occurs after mid-century, if at all, and in the country’s South Island. Comparing times and extents of emergence across hydrological variables sheds further light on which variables are more likely to act as hydrological sentinels of climate change, with implications for monitoring design. And comparing extents of emergence among emissions scenarios sheds light on spatial benefits of mitigation. In terms of adaptation, the low rates of emergence combined with lags between effects and detection support a phased but flexible transition from stationary to non-stationary management methods in a patchwork manner across the country.