Is the governance of the Thau coastal lagoon ready to face climate change impacts?

• Climate change will increase temperature and decrease runoff in the Thau catchment.
• Climate change challenges for local water uses are not perceived by local stakeholders.
• Regional water management provides security for domestic use including tourism and irrigation.
• Regional water management increases the vulnerability of local water governance.
• CLIMB EU FP7 project, CLIWASEC cluster, multidisciplinary analyses.

The present paper provides a reflection on threats to integrated management of the Thau coastal lagoon due to climate change and the multi-scalar water scarcity adaptation strategy. This study proposes first to depict the Thau water governance assessed through a water use and social network analysis and its capacity to manage water quality. Next, this paper provides a downscaled study on the climate change impacts on the hydrological budget of the entire Thau catchment in 2041–2070 compared with the 1971–2000 reference period, a methodology developed during the CLIMB EU research program. Following local climate change impacts, the importation of a new water resource to secure water uses is presented in regards to the capacity of local water governance to maintain coherence between integrated land planning and integrated water management planning based on water quality issues of the Thau coastal lagoon. The study underlines that although the water uses are currently secured thanks to the regional transfer of water, they are not coherent with local water management and create new vulnerabilities in the context of climate change. Moreover, the regional decision to end financial support for the more efficient, existing network for the water quality survey of regional coastal lagoons breaks up the local water governance. This paper demonstrates why keeping this network would have been absolutely necessary for encouraging a governance capable of proposing sustainable solutions to water quality challenges induced by climate change.