Water under a Changing and Uncertain Climate: Lessons from Climate Model Ensembles

Abstract:

Uncertainties posed by climate change and rapidly rising global water demand will place unprecedented pressures on already strained water resource systems. Successfully planning for these future changes requires a sound scientific understanding of the timing, location, and magnitude of climate change impacts on water needs and availability – not only on average trends, but also on interannual and decadal variability and associated uncertainties. In recent years, two types of large ensemble runs ­of climate projections have become available, those from groups of more than 20 different climate ­models, and those from repeated runs of several individual models. These have provided new approaches to the probabilistic evaluation of both climate change and the resulting effects on water resources. Using a range of available climate model ensembles, this research explores the spatial and temporal patterns of uncertainty in projected river runoff and irrigation water requirements. The research compares the time of emergence of anthropogenic signals in precipitation against those of runoff and irrigation needs, considering emergence from both interannual and inter-model noise. Implications of the patterns of model uncertainty are discussed for water management in the U.S. and globally.