Flood projections within the Niger River Basin under future land use and climate change.
This study assesses future flood risk in the Niger River Basin (NRB), for the first time considering the simultaneous effects of both projected climate change and land use changes. For this purpose, an ecohydrological process-based model (SWIM) was set up and validated for past climate and land use dynamics of the entire NRB. Model runs for future flood risks were conducted with an ensemble of 18 climate models, 13 of them dynamically downscaled from the CORDEX Africa project and five statistically downscaled Earth System Models. Two climate and two land use change scenarios were used to cover a broad range of potential developments in the region. Two flood indicators (annual 90th percentile and the 20-year return flood) were used to assess the future flood risk for the Upper, Middle and Lower Niger as well as the Benue. The modeling results generally show increases of flood magnitudes when comparing a scenario period in the near future (2021-2050) with a base period (1976-2005). Land use effects are more uncertain, but trends and relative changes for the different catchments of the NRB seem robust. The dry areas of the Sahelian and Sudanian regions of the basin show a particularly high sensitivity to climatic and land use changes, with an alarming increase of flood magnitudes in parts. A scenario with continuing transformation of natural vegetation into agricultural land and urbanization intensifies the flood risk in all parts of the NRB, while a "regreening" scenario can reduce flood magnitudes to some extent. Yet, land use change effects were smaller when compared to the effects of climate change. In the face of an already existing adaptation deficit to catastrophic flooding in the region, the authors argue for a mix of adaptation and mitigation efforts in order to reduce the flood risk in the NRB.
Potsdam Institute for Climate Impact Research (PIK), P.O. Box 60 12 03, 14412 Potsdam, Germany. Electronic address: aich@pik-potsdam.de.
Valentin
V
Aich
Potsdam Institute for Climate Impact Research (PIK), P.O. Box 60 12 03, 14412 Potsdam, Germany. Electronic address: liersch@pik-potsdam.de.
Stefan
S
Liersch
Potsdam Institute for Climate Impact Research (PIK), P.O. Box 60 12 03, 14412 Potsdam, Germany. Electronic address: vetter@pik-potsdam.de.
Tobias
T
Vetter
Potsdam Institute for Climate Impact Research (PIK), P.O. Box 60 12 03, 14412 Potsdam, Germany.
Samuel
S
Fournet
Swedish Meteorological and Hydrological Institute (SMHI), SE-601 76 Norrköping, Sweden. Electronic address: jafet.andersson@smhi.se.
Jafet C M
JCM
Andersson
Italian National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA), Centro Ricerche Casaccia Via Anguillarese 301, I-00123 Roma, Italy. Electronic address: sandro.calmanti@enea.it.
Sandro
S
Calmanti
Wetlands International (WI), P.O. Box 471, 6700 AL Wageningen, The Netherlands. Electronic address: frank.vanweert@wetlands.org.
Frank H A
FHA
van Weert
Potsdam Institute for Climate Impact Research (PIK), P.O. Box 60 12 03, 14412 Potsdam, Germany. Electronic address: hattermann@pik-potsdam.de.
Fred F
FF
Hattermann
Institute of Ecology, Technische Universität Berlin, Ernst-Reuter-Platz 1, 10587 Berlin, Germany. Electronic address: eva.paton@tu-berlin.de.
Eva N
EN
Paton
Climate change; Cordex; Ecohydrological modeling; Floods; Land use change; Niger