HYMEX

HyMeX aims at a better understanding, quantification and modelling of the hydrological cycle in the Mediterranean, with emphasis on the predictability and evolution of extreme weather events, inter-annual to decadal variability of the Mediterranean coupled system, and associated trends in the context of global change. The multidisciplinary research and associated database developed within HyMeX aim to improve the observational and modelling systems, better predict extreme events, simulate the long-term water-cycle, and provide guidelines for adaptation measures.

Presentation

The hydrological cycle in the Mediterranean is a key environmental and socio-economic question for a wide region encompassing southern Europe, northern Africa and the Middle East. The lack of readiness and mitigation strategies could result in critical situations, in particular in case of extreme events and inadequate evaluation of climate change impacts. To face environmental challenges, progress has to be made in the understanding of the Mediterranean climate.

HyMeX (HYdrological cycle in the Mediterranean EXperiment) aims at a better understanding and quantification of the hydrological cycle and related processes in the Mediterranean, with emphasis on high-impact weather events, inter-annual to decadal variability of the Mediterranean coupled system, and associated trends in the context of global change.

Launched by the French scientific community, the definition of HyMeX has started with the drafting of a White Book released in 2007 identifying the main scientific challenges for HyMeX regarding the Mediterranean water cycle, and making suggestions on how to address them. HyMeX has since extended to the international community, produced an International Science Plan (ISP), and is currently working at its International Implementation Plan (IIP).

Motivations

A unique coupled system
The Mediterranean region features a nearly closed sea surrounded by urbanized littorals and mountains from which numerous rivers originate. This results in many interactions and feedback between oceanic, atmospheric, and hydrological processes, as well as anthropogenic activities. To understand the prominent role of such interactions in the regional climate and ecosystems, research should now not only focus on processes within each Earth compartment, but also on interface processes and feedback loops in order to make significant progress in the comprehension and prediction of the Mediterranean water cycle and related phenomena.

High impact weather events
The Mediterranean climate is also influenced by both sub-tropical and mid-latitude climate dynamics and is therefore very sensitive to global climate change. Extreme weather events, including heavy precipitation and flash-flooding during the fall season, severe cyclogenesis associated with strong winds and large sea waves during winter, and heat waves and droughts accompanied by forest fires during summer, regularly affect the Mediterranean region causing heavy damages and human loss. The capability to predict such high-impact events remains weak because of the contribution of very fine-scale processes and their non-linear interactions with the larger scale processes. Advances in the identification of the predominant processes and particularly of their interactions at the different scales are needed in order to better forecast these events and reduce uncertainties on the prediction of their evolution (e.g. frequency, intensity) under the future climate. These issues are not only of primary importance for providing a tangible basis for early warning procedures and mitigation measures designed to avoid loss of life and reduce damage, but also to assess their impacts on the terrestrial and marine ecosystems, some of which may be irreversible.

Water resource issues
Freshwater is rare and unevenly distributed in time and space with few short duration heavy precipitation and long drought periods. In numerous countries, almost all the rivers are either intermittent or ephemeral. Water resource is a critical issue in a large part of the Mediterranean basin: with less than 1000 m3 per person per year, 180 million people face water scarcity, which represents more than one half of the world’s so-called water poor population. Increasing water demand and climate change add to this background. During the second half of the 20th century, water demand has increased twofold. Progress has to be made in the monitoring and modelling of the Mediterranean hydrological continental cycle in order to better predict its future evolution and impacts on water resources for appropriate management.

A hot-spot for the climate change
Mediterranean regions have been identified as one of the two main hot-spots of climate change, meaning that climate is especially responsive to global change in this area. Large decrease in mean precipitation and increase in precipitation variability during dry (warm) season are expected as well as large increase in temperature (+1.4 to +5.8’C in 2100). Large uncertainties however remain on the future evolution of climate in the Mediterranean. Progress has to be made in the monitoring and modelling of the Mediterranean coupled climate system (atmosphere-land-ocean) in order to quantify the on-going changes and to better predict their future evolution as guidelines for the development of adaptation measures.

The HyMeX science objectives

Considering the science and societal issues motivating HyMeX, the programme aims to :

• improve our understanding of the water cycle, with emphasis on extreme events,
• by monitoring and modelling the Mediterranean atmosphere-land-ocean coupled system, its variability from the event to the seasonal and interannual scales,
• and its characteristics over one decade (2010-2020) in the context of global change,
• assess the social and economic vulnerability to extreme events and adaptation capacity.

The multidisciplinary research and the database developed within HyMeX should contribute to:

• improve observational and modelling systems, especially for coupled systems,
• better predict extreme events,
• simulate the long-term water-cycle more accurately,
• provide guidelines for adaptation measures, especially in the context of global change.