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| Titel |
GRACE water storage estimates for the Middle East and other regions with significant reservoir and lake storage |
| VerfasserIn |
L. Longuevergne, C. R. Wilson, B. R. Scanlon, J. F. Crétaux |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 17, no. 12 ; Nr. 17, no. 12 (2013-12-05), S.4817-4830 |
| Datensatznummer |
250086015
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| Publikation (Nr.) |
 copernicus.org/hess-17-4817-2013.pdf |
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| Zusammenfassung |
While GRACE (Gravity Recovery and Climate Experiment) satellites are
increasingly being used to monitor total water storage (TWS) changes
globally, the impact of spatial distribution of water storage within a basin
is generally ignored but may be substantial. In many basins, water is often
stored in reservoirs or lakes, flooded areas, small aquifer systems, and
other localized regions with areas typically below GRACE resolution
(~200 000 km2). The objective of this study
was to assess the impact of nonuniform water storage distribution on GRACE
estimates of TWS changes as basin-wide averages, focusing on surface water
reservoirs and using a priori information on reservoir storage from radar
altimetry.
Analysis included numerical experiments testing effects of location and
areal extent of the localized mass (reservoirs) within a basin on basin-wide
average water storage changes, and application to the lower Nile (Lake
Nasser) and Tigris–Euphrates basins as examples. Numerical experiments show
that by assuming uniform mass distribution, GRACE estimates may under- or
overestimate basin-wide average water storage by up to a factor of
~2, depending on reservoir location and areal extent.
Although reservoirs generally cover less than 1% of the basin area, and
their spatial extent may be unresolved by GRACE, reservoir storage may
dominate water storage changes in some basins. For example, reservoir
storage accounts for ~95% of seasonal water storage
changes in the lower Nile and 10% in the Tigris–Euphrates. Because
reservoirs are used to mitigate droughts and buffer against climate
extremes, their influence on interannual timescales can be large.
For example, TWS decline during the 2007–2009 drought in the Tigris–Euphrates basin measured by GRACE was ~93 km3. Actual
reservoir storage from satellite altimetry was limited to 27 km3, but
their apparent impact on GRACE reached 45 km3, i.e., 50% of GRACE
trend. Therefore, the actual impact of reservoirs would have been greatly
underestimated (27 km3) if reservoir storage changes were assumed
uniform in the basin. Consequently, estimated groundwater contribution from
GRACE would have been largely overestimated in this region if the actual
distribution of water was not explicitly taken into account.
Effects of point masses on GRACE estimates are not easily accounted for via
simple multiplicative scaling, but in many cases independent information may
be available to improve estimates. Accurate estimation of the reservoir
contribution is critical, especially when separating estimating groundwater
storage changes from GRACE total water storage (TWS) changes. Because the
influence of spatially concentrated water storage – and more generally
water distribution – is significant, GRACE estimates will be improved by
combining independent water mass spatial distribution information with GRACE
observations, even when reservoir storage is not the dominant mechanism. In
this regard, data from the upcoming Surface Water Ocean Topography (SWOT)
satellite mission should be an especially important companion to GRACE-FO
(Follow-On) observations. |
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