Climate change impact on coastal aquifers in France –vulnerability of coastal aquifers due to sea level rise Nathalie Dörfliger n.dorfliger@brgm.fr Head of Water division per interim brgm, Orléans – France Workshop “Climat Change Impacts on Groundwater” Warsaw, Poland, 12th October 2011

Background Sea level rise According IPCC (2007) respectively Cazenave & Llovel, (2009) at global level : 1993-2003 : 3,1 ± 0,7 mm/year and 3,4 ± 0,4 mm/year for 1993-2008 According to IPCC (2007): 18 to 59 cm from scenario B1 to scenario A1FI for 1980-1999 to 2090-2099 At French Metropolitan level: between 1 and 2,5 mm/year for 1993-2007 period; for overseas territories: short time series (less than 10 years) Selected sea level variations: 0,2cm, 0,6cm, 1m and + 2m to study the impact on coastal aquifers. Source: LEGOS/GOHS Spatial distribution of the sea level variation velocities (1993-2007) based on Topex/Poseidon and Jason-1 : Zoom on the Mediterranean sea. Source :http://www.legos.obsmip.fr/fr/equipes/gohs/resultats/b1_nivmer1. Spatial distribution of the sea level variation velocities (1993-2007) based on Topex/Poseidon and Jason-1 data

Background Which vulnerability on coastal aquifers in Metropolitan France and in the Overseas French territories ? Which impact of sea level variation on sea water intrusion on coastal aquifers ? How to identify vulnerable aquifers at national level considering various types of aquifers and > 5000km coastline length ? Chang et al. 2011

Methodology at national and regional level Coastal aquifers status Metropolitain France and overseas territories State of knowledge of coastal aquifers Data base and mappping Selection of coastal aquifers for modelling Vulnerability mapping at various scales Groundwater modeling at aquifer scale Methodological development Tests at regional scale Groundwater modeling on two aquifers Interpretation Recommendations Results interpretation Recommendation in terms of management and survey before adaptation solutions 1 2 3 Considering: Sea level rise scenarios Not considered directly: CC on recharge and precipitation patterns Water demand increase on coastal areas

Vulnerability mapping of coastal aquifers at national level Mapping of the coastal aquifer area (5km width) Classification of sensitivity to present sea water intrusion Mapping of point data of salinity of groundwater Mapping of low elevation areas with Digital topography model Impact of sea level rise considering two up to three classes Demographical pressure mapping as well water supply works density Vulnerability mapping of coastal aquifers at national level for sea level rise

Sensibility of coastal aquifers BDLISA GW referential entities Selection up to 8 regional areas to carry out GALDIT method and on one groundwater modeling Caen coastal plain Marais Poitevin Garonne estuary Roussillon plain Crau aquifer – Rhône Delta Var alluvial aquifer

Vulnerability mapping at regional scale GALDIT method (Ferreira et al., 200; CHACHADI and LOBO-FERREIRA (2005)) Paramètres Weight Ranking Very Low Low Middle High 2.5 5 7.5 10 G : Groundwater occurrence – aquifer type 1 Bounded aquifer Leaky confined unconfined confined A : aquifer hydraulic conductivity (m/day) 3 < 5 5 - 10 10-40 > 40 L : GW level depth/ sea water level (m) 4 < 1 1 – 1.5 1.5 - 2 > 2 D : Distance to the coast (m) 2 < 500 500-750 750-1000 > 1000 I : Impact of sea water intrusion (ppm) T : Thickness of the aquifer (m) 5 – 7.5 7.5-10 > 10 Vulnerability classes GALDIT index High vulnerability > 7.5 Mean vulnerability 5 – 7.5 Low vulnerability < 5 D _ map G_ map Final vulnerability map

GW modeling Marais Poitevin Similar GW abstraction volumes at present day Only in first approximation hydrodynamic simulation + 1m for sea level increase High water stage dry year Low water stage dry year Initial + 1 m Impact on several kilometers inland High impact for low water stage and dry years Further GW modeling integrating salinity data, under progress

Vulnerability mapping at regional scale Example in Overseas Territories GALDIT vulnerability classes La Réunion Island High vulnerability Mean vulnerability Low vulnerability Impact of sea level rise on areas based on topography < 0,6 m 0,6 to 2 m > 2m to 4 m > 1000 mS/cm

Comparison GW modeling and GALDIT method Groundwater modeling Reference Groundwater modeling Sea level + 1 m Submersion areas GALDIT – sea level + 1m GALDIT– sea level + 2m

Conclusions and perspectives Sea level rise will occur but demography pressure will play a major role on sea water intrusion on coastal aquifers Uncertainties of climatic models on Overseas territories; less increase on Mediterranean Sea Two levels of vulnerability mapping: national and regional GALDIT method gives a first approximation in comparison to GW models; further works under progress to improve the method Needs to link with demography pressure on water captures abstraction volumes Focus on high vulnerability areas to implement dedicated GW salinity monitoring network Thank you for your attention !