posted on 2019-02-12, 00:00authored bySara Alian, Alex Mayer, Ann Maclean, David Watkins, Ali Mirchi
Coarse
temporal (i.e., annual) and spatial (i.e., watershed) scales camouflage
water stress associated with withdrawals from surface water and groundwater
sources. To address this “curse of scale”, we developed
a framework to characterize water stress at different time scales
and at fine spatial scales that have not been explored before. Our
framework incorporates surface water–groundwater interactions
by accounting for spatially cumulative consumptive and nonconsumptive
use impacts and associated changes in flow due to depletion and return
flow along stream networks. We apply the framework using a rich data
set of water withdrawals from more than 6800 principal facilities
(i.e., withdrawal capacity >380 000 L/day) across the U.S.
Great Lakes Basin. Results underscore the importance of spatiotemporal
scale and return flows when characterizing water stress. Although
the majority of catchments in this water-rich region do not experience
large stress, a number of small headwater catchments with sensitive
streams are vulnerable to flow depletion caused by surface water and
shallow groundwater withdrawals, especially in a high-withdrawal,
low-flow month (e.g., August). The return flow from deep groundwater
withdrawals compensates for the streamflow depletion to the extent
that excess flow is likely in many catchments. The improved ability
to pinpoint the imbalance between natural water supply and withdrawals
based on stream-specific ecological water stress thresholds facilitates
protecting fragile aquatic ecosystems in vulnerable catchments.