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| Titel |
Evaluation of the ISBA-TRIP continental hydrologic system over the Niger basin using in situ and satellite derived datasets |
| VerfasserIn |
V. Pedinotti, A. Boone, B. Decharme, J. F. Crétaux, N. Mognard, G. Panthou, F. Papa, B. A. Tanimoun |
| 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. 6 ; Nr. 16, no. 6 (2012-06-26), S.1745-1773 |
| Datensatznummer |
250013332
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| Publikation (Nr.) |
 copernicus.org/hess-16-1745-2012.pdf |
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| Zusammenfassung |
| During the 1970s and 1980s, West Africa has faced extreme climate
variations with extended drought conditions. Of particular
importance is the Niger basin, since it traverses a large part of the
Sahel and is thus a critical source of water for an ever-increasing
local population in this semi arid
region. However, the understanding of the hydrological processes over
this basin is currently limited by the lack of spatially distributed
surface water and discharge measurements. The purpose of this study is to
evaluate the ability of the ISBA-TRIP continental hydrologic system to
represent key processes related to the hydrological cycle of the Niger
basin. ISBA-TRIP is currently used within a coupled global climate model,
so that the scheme must represent the first order processes which are
critical for representing
the water cycle while retaining a limited number of parameters and a
simple representation of the physics. To this end, the
scheme uses first-order approximations to account
explicitly for the surface river routing, the
floodplain dynamics, and the water storage using a deep aquifer
reservoir. In the current study, simulations are done at a 0.5 by
0.5° spatial resolution over the 2002–2007 period (in order to
take advantage of the recent satellite record and data from the African
Monsoon Multidisciplinary Analyses project, AMMA). Four
configurations of the model are compared to evaluate the separate
impacts of the flooding scheme and the aquifer on the water cycle.
Moreover, the model is forced by two different rainfall datasets to
consider the sensitivity of the model to rainfall input
uncertainties. The model is evaluated using
in situ discharge measurements as well as satellite derived flood
extent, total continental water storage changes and river height
changes. The basic analysis of in situ discharges confirms the
impact of the inner delta area, known as a significant flooded area, on the discharge, characterized
by a strong reduction of the streamflow after the delta compared to
the streamflow before the delta. In the simulations, the flooding
scheme leads to a non-negligible increase of evaporation over large
flooded areas, which decreases the Niger river flow by 15% to
50% in the locations situated after the inner delta
as a function of the input rainfall dataset used as forcing.
This improves the simulation of the river discharge downstream of the
delta, confirming the need for coupling the land surface scheme with the flood model. The deep aquifer reservoir improves Niger low
flows and the recession law during the dry season.
The comparison with 3 satellite products from the
Gravity Recovery and Climated Experiment (GRACE)
shows a non negligible contribution of the deeper soil layers to
the total storage (34% for groundwater and aquifer). The
simulations also show a non negligible sensitivity of the simulations to
rain uncertainties especially concerning the discharge. Finally,
sensitivity tests show that a good parameterization of routing
is required to optimize simulation errors. Indeed, the
modification of certain key parameters which can be observed from
space (notably river height and flooded zones height changes and
extent) has an impact on the
model dynamics, thus it is suggested that improving the model input
parameters using future developments in remote sensing technologies
such as the joint CNES-NASA satellite project SWOT (Surface Water Ocean
Topography), which will provide water heights and extentat land surface with an unprecedented 50–100 m resolution and precision. |
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