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| Titel |
Global runoff anomalies over 1993–2009 estimated from coupled Land–Ocean–Atmosphere water budgets and its relation with climate variability |
| VerfasserIn |
S. Munier, H. Palanisamy, P. Maisongrande, A. Cazenave, E. F. Wood |
| 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 ; 16, no. 10 ; Nr. 16, no. 10 (2012-10-16), S.3647-3658 |
| Datensatznummer |
250013519
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| Publikation (Nr.) |
 copernicus.org/hess-16-3647-2012.pdf |
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| Zusammenfassung |
| Whether the global runoff (or freshwater discharge from land to the ocean)
is currently increasing and the global water cycle is intensifying is still
a controversial issue. Here we compute land–atmosphere and ocean–atmosphere
water budgets and derive two independent estimates of the global runoff over
the period 1993–2009. Water storage variations in the land, ocean and
atmosphere reservoirs are estimated from different types of data sets:
atmospheric reanalyses, land surface models, satellite altimetry and in situ
ocean temperature data (the difference between altimetry based global mean
sea level and ocean thermal expansion providing an estimate of the ocean
mass component). These data sets are first validated using independent data,
and then the global runoff is computed from the two methods. Results for the
global runoff show a very good correlation between both estimates. More
importantly, no significant trend is observed over the whole period.
Besides, the global runoff appears to be clearly impacted by large-scale
climate phenomena such as major ENSO events. To infer this, we compute the
zonal runoff over four latitudinal bands and set up for each band a new
index (combined runoff index) obtained by optimization of linear
combinations of various climate indices. Results show that, in particular,
the intertropical and northern mid-latitude runoffs are mainly driven by
ENSO and the Atlantic multidecadal oscillation (AMO) with opposite behavior.
Indeed, the zonal runoff in the intertropical zone decreases during major El
Niño events, whereas it increases in the northern mid-latitudes,
suggesting that water masses over land are shifted northward/southward
during El Niño/La Niña. In addition to this study, we propose an
innovative method to estimate the global ocean thermal expansion. The method
is based on the assumption that the difference between both runoff estimates
is mainly due to the thermal expansion term not accounted for in the
estimation of the ocean mass. We find that our reconstructed thermal
expansion time series compares well with two existing data sets in terms of
year-to-year fluctuations but somewhat differs on longer (multi-year) time
scales. Possible explanations include non negligible steric variations from
the deep ocean. |
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