New Zealand River Hydrology under Late 21st Century Climate Change

Daniel B G Collins

doi:10.3390/w12082175

Abstract

Climate change is increasingly affecting the water cycle and as freshwater plays a vital role in countries’ societal and environmental well-being it is important to develop national assessments of potential climate change impacts. Focussing on New Zealand, a climate-hydrology model cascade is used to project hydrological impacts of late 21st century climate change at 43,862 river locations across the country for seven hydrological metrics. Mean annual and seasonal river flows validate well across the whole model cascade, and the mean annual floods to a lesser extent, while low flows exhibit a large positive bias. Model projections show large swathes of non-significant effects across the country due to interannual variability and climate model uncertainty. Where changes are significant, mean annual, autumn, and spring flows increase along the west and south and decrease in the north and east. The largest and most extensive increases occur during winter, while during summer decreasing flows outnumber increasing. The mean annual flood increases more in the south, while mean annual low flows show both increases and decreases. These hydrological changes are likely to have important long-term implications for New Zealand’s societal, cultural, economic, and environmental well-being.

Highlights

Climate change is increasingly affecting global, regional, and local water cycles, impacts that are projected to continue over the course of the 21st century [1,2,3,4,5,6]
For the mean annual and seasonal flows there is little scatter about the 1:1 line, with Nash-Sutcliff Efficiency (NSE) ranging from 0.89 to 0.97 (Table 1). As this is applied nationally, this potential aclimate changetoeffects from the combined from effectsone of modelled climatevaries variability suggests good ability distinguish catchments another
This research presents the validation of a climate-hydrology model cascade and its application in projecting changes in 21st century river hydrology across New Zealand

Summary

Introduction

Climate change is increasingly affecting global, regional, and local water cycles, impacts that are projected to continue over the course of the 21st century [1,2,3,4,5,6]. An important part of climate change adaptation is the use of impact studies to inform decision-making For hydrological impacts, these studies often follow a similar top-down modelling cascade [14]: scenarios of future emissions, encapsulated by Representative Concentration Pathways (RCPs) [15], are used to drive General Circulation Models (GCMs), whose outputs are downscaled to a more useful resolution, bias-corrected, and used to drive hydrological models (HMs). These studies often follow a similar top-down modelling cascade [14]: scenarios of future emissions, encapsulated by Representative Concentration Pathways (RCPs) [15], are used to drive General Circulation Models (GCMs), whose outputs are downscaled to a more useful resolution, bias-corrected, and used to drive hydrological models (HMs) Studies vary in their choice of scale (global, continental, national, or catchment), and in their choice of RCPs, GCMs, downscaling, bias-correction, and HMs, each adding uncertainty to the final results [16]

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