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A hydrologic drying bias in water-resource impact analyses of anthropogenic climate change

Journal of the American Water Resources Association

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https://doi.org/10.1111/1752-1688.12538

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Abstract

For water-resource planning, sensitivity of freshwater availability to anthropogenic climate change (ACC) often is analyzed with “offline” hydrologic models that use precipitation and potential evapotranspiration (Ep) as inputs. Because Ep is not a climate-model output, an intermediary model of Ep must be introduced to connect the climate model to the hydrologic model. Several Ep methods are used. The suitability of each can be assessed by noting a credible Ep method for offline analyses should be able to reproduce climate models’ ACC-driven changes in actual evapotranspiration in regions and seasons of negligible water stress (Ew). We quantified this ability for seven commonly used Ep methods and for a simple proportionality with available energy (“energy-only” method). With the exception of the energy-only method, all methods tend to overestimate substantially the increase in Ep associated with ACC. In an offline hydrologic model, the Ep-change biases produce excessive increases in actual evapotranspiration (E), whether the system experiences water stress or not, and thence strong negative biases in runoff change, as compared to hydrologic fluxes in the driving climate models. The runoff biases are comparable in magnitude to the ACC-induced runoff changes themselves. These results suggest future hydrologic drying (wetting) trends likely are being systematically and substantially overestimated (underestimated) in many water-resource impact analyses.

Additional publication details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
A hydrologic drying bias in water-resource impact analyses of anthropogenic climate change
Series title:
Journal of the American Water Resources Association
DOI:
10.1111/1752-1688.12538
Volume:
53
Issue:
4
Year Published:
2017
Language:
English
Publisher:
American Water Resources Asssociation
Contributing office(s):
National Research Program - Eastern Branch
Description:
17 p.
First page:
822
Last page:
838