Abstract
While anthropogenic climate change poses a risk to freshwater resources across the globe through increases in evapotranspiration and temperature, it is essential to quantify the risks at local scales in response to projected trends in both freshwater supply and demand. In this study, we use empirical modeling to estimate the risks of municipal water shortages across North America by assessing the effects of climate change on streamflow and urban water demand. In addition, we aim to quantify uncertainties in both supply and demand predictions. Using streamflow data from both the US and Canada, we first cluster 4,290 streamflow gauges based on hydrograph similarity and geographical location. We develop a set of multiple linear regression (MLR) models, as a simplified analog to a distributed hydrological model, with minimum input data requirements. These MLR models are calibrated to simulate streamflow for the 1993–2012 period using the ERA5 climate reanalysis data. The models are then used to predict streamflow for the 2080–2099 period in response to two climate scenarios (RCP4.5 and RCP8.5) from five global climate models. Another set of MLR models are constructed to project seasonal changes in municipal water consumption for the clustered domains. The models are calibrated against collected data on urban water use from 47 cities across the study region. For both streamflow and water use, we quantified uncertainties in our predictions using stochastic weather generators and Monte Carlo methods. Our study shows the strong predictive power of the MLR models for simulating both streamflow regimes (Kling-Gupta efficiency >0.5) and urban water use (correlation coefficient ≈0.7) in most regions. Under the RCP4.5 (RCP8.5) emissions scenario, the West Coast, the Southwest, and the Deep South (South-Central US and the Deep South) have the highest risk of municipal water shortages. Across the whole domain, the risk is the highest in the summer season when demand is high. We find that the uncertainty in projected changes to the water demand is substantially lower than the uncertainty in the projected changes to the supply. Regions with the highest risk of water shortages should begin to investigate mitigation and adaptation strategies.
Highlights
Based on current climate projections, global mean temperature is likely to increase by at least 2°C, relative to the 1850s, by the end of the century (Forster et al, 2020)
The probability of water shortage was calculated across the U.S by Foti et al (2012) and probabilities were highest in the same areas as our study indicated, namely the southwestern United States and the coast of California, though they showed a high risk for the central US as well
We presented a new method for quantifying future risks of municipal water shortages across North America in response to climate change
Summary
Based on current climate projections, global mean temperature is likely to increase by at least 2°C, relative to the 1850s, by the end of the century (Forster et al, 2020). In the US, the regions most severely hit by recent droughts include the Central US (Basara et al, 2019), California (Howitt et al, 2015), as well as the relatively wet areas in the US South (Chen et al, 2012) Further droughts in these areas as well as more widespread droughts throughout North America may come as a result of declining summer precipitation in the latter half of the 21st century, warming Pacific and North Atlantic Oceans, and escalating climate variability (Rosegrant and Cai, 2002; MacDonald et al, 2008; Schwalm et al, 2012). Snow is crucial in the western United States for sustaining water demand, decreasing snowpack as a result of increasing temperatures threatens water sustainability, though uncertainties remain large (Mankin et al, 2015)
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