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Adaptation to climate change requires a good understanding of the regional impacts of this phenomenon, especially in vulnerable regions. One of the challenges currently facing research thus consists in developing models that are based on global predictions of warming and which can be used to assess its impacts on the regional scale (water resources, productivity of land, extreme events). The project aims to develop a regional modelling platform focusing on the Mediterranean basin. It will be based on coupling of existing regional models of the various components of the Earth system (ocean, continental land masses, atmospheric composition) and interfacing with the IPSL's global climate model.
The Fourth IPCC Assessment Report forecasts an increase in the earth's average temperature of between 1.4°C and 5.8°C over the 21st century, accompanied by a rise in sea levels of between 9 and 88 cm. This rapid change in the global climate is making it more unstable, resulting in more frequent natural disasters (cyclones, droughts, floods, etc...) in certain parts of the world. Among other consequences, these changes are set to cause radical disruption to agriculture, large population movements as people abandon disaster-struck regions (such as flooded coastal plains and areas blighted by desertification) for less-affected areas, and heightened political tensions.
The vulnerability of human populations and natural systems in the face of climate change varies greatly between geographic regions and between populations. The natural and social systems in each region vary, resulting in differences in the ability to adapt to the impact of current and future climate changes. Furthermore, each regional system is affected both by large-scale climate teleconnections and by specific local processes. As these differences raise a number of serious concerns, it appears crucial to fully understand the space-time interactions that occur at the regional scale, with particular focus on past variability and vulnerability of key regions to a range of constraints.
MORCE MED aims to address these questions for the Mediterranean region, which is a particularly vulnerable region featuring an almost-enclosed basin with pronounced orography around its perimeter, a sharply-contrasted climate and heavy urbanization. Interactions and feedback effects between the various domains in this basin play a decisive role in the geophysical and biological dynamics. Forecasting extreme events in the region (such as intense rainfall and flooding in autumn, strong winds and rough seas - whether related or unrelated to Mediterranean cyclogenesis, droughts and forest fires) is difficult, owing to a lack of information about their preconditioning, which involves a whole range of hierarchically-interlocking processes that act in a non-linear manner at the smallest of scales. We require a better understanding of the role of this hierarchy in the generation of extreme events in the Mediterranean region, in order to better evaluate their predictability and improve forecasting performance. Furthermore, due to the basin's strong topographical influence we need to develop integrated approaches by regionalization, in order to identify the mechanisms underpinning the Mediterranean region's climate response to global warming.
Currently, the global climate is represented using large-scale modelling software with a grid resolution of the order of 100 km. This resolution is too coarse, however, to reproduce phenomena that operate on a near-human scale, such as those that affect the Mediterranean basin. Exploring this region's climate will therefore require considerable research upstream, including the development of a coupled regional modelling platform that makes it possible to quantify the earth system's regional response to large-scale parameter forcing.
Part 1: Development of the coupled regional modelling platform (MORCE)
Regional models (grid resolution: approx. 10km) >> Coupling
ORCHIDEE: continental surface layers (vegetation)
CHIMERE: atmospheric chemistry
ECO3M: marine biogeochemistry
Global models >> Coupling
ORCHIDEE: continental surface layers
INCA: atmospheric chemistry
PISCES: marine biogeochemistry
Developing the platform entails inter-coupling the various regional models and then forcing them with the results produced by the global models, some of which are themselves also coupled.
Part 2: Use of the modeling platform to study the mechanisms at the interfaces of the present-day Mediterannean regional climate
Atmosphere-continental land mass and ocean-atmosphere interactions
The water cycle in the Mediterranean basin is particularly complex: the water balance (evaporation-precipitation-runoff) at the scale of the basin is negative, being compensated only by an intake of water from the Atlantic Ocean; mainland water resources are in a critical state in most regions around the Mediterranean Sea, resulting in severe droughts, and regular episodes of intense precipitation cause extensive damage during the autumn and winter months. Phenomena occurring at a regional scale (from a few kilometres to a few hundred kilometres) play a decisive role in the various aspects of the Mediterranean water cycle. In order to describe these phenomena more precisely, the research scientists aim to study two aspects: droughts and how they spread depending on surface conditions; and the air/sea evaporation flows and their impacts on cloud formation and precipitation as well as thermohaline circulation in the Mediterranean Sea.
Chemical composition of the atmosphere and impacts on vegetation
The recurrent heat waves of recent years are causing the ground to dry out, which may affect the processes whereby trace species (gases and particles) are produced and lost. This drying-out affects the nature of the vegetation present, and the effectiveness with which it absorbs and fixes gases as dry deposits. Consequently, the more severe the heat wave, the more active the photochemistry. As the temperature rises, the ozone concentration in the troposphere (where it is toxic to humans) increases, while at the same time less ozone is deposited due to the drying-out of the soil. At this stage of the project, the aim is to determine whether this feedback could become a major new "source" of ozone concentration in the planetary boundary layer, and if so, to quantify the weight of this phenomenon as a share of all pollution processes.
Study of uncertainties of the MORCE platform
The uncertainties relating to regional modeling (large-scale forcing, digital distribution of the regional platform, etc.) will be studied by comparing the results produced by the MORCE platform with the numerous datasets available at IPSL (satellites, in situ data, campaign data, etc.). This research should also make it possible to analyze the benefit of coupled simulations compared with forced simulations.
Part 3: Use of the modelling platform to study the sensitivity of the Mediterranean regional climate to global warming
• Description of the climate in the Atlantic/Mediterranean region and study of large-scale weather regime variability in the context of global warming
• Study of variability of the water cycle and regional chemical compositions in a context of global change
Part 4: Provision of the MORCE platform for use via other Web interfaces
• Definition of the principle underpinning climate models, Jean-Marc Jancovici (in French)
• MedClivar (Mediterranean climate variability and predictability): international project that aims to coordinate and promote research into the Mediterranean climate.
• Projects in the Mediterranean programme
HyMex (Hydrologic cycle in Mediterranean experiment) seeks to enhance our characterization and understanding of the water cycle in the Mediterranean basin, considering the various compartments (i.e. ocean, atmosphere, biogeochemistry and the surface and hydrological systems of the continental land mass) and the couplings between them at each time scale.
CharMex (Chemistry Aerosol Mediterranean Experiment) aims to study the troposphere chemistry and aerosols in the Mediterranean region, and assess their impacts on the radiation balance, the hydrological cycle, air quality and marine biogeochemistry.
MerMex (Marine Ecosystems Response in the Mediterranean Experiment programme) has the goal of improving our understanding of Mediterranean marine ecosystems in order to better anticipate changes in them. The scientists involved are studying how ecosystems respond to variations in the physico-chemical forcing caused by changes in environmental conditions and increasing human pressure.
• The CICLE project (Calcul Intensif pour le Climat et l'Environnement (High-performance computing for the climate and environment)) aims to develop a new generation of models able to take full advantage of the power of current and future supercomputers in order to perform cutting-edge simulations that will lead to major breakthroughs both in our understanding of physical phenomena and in our predictive capabilities. Three simulations are planned for the final stage of the project, one of which is a simulation of the Mediterranean regional climate over the period 1950-2050, based on a limited-area coupled model nested in a global coupled model.
• CIRCE (Climate Change and Impact Research: the Mediterranean Environment) is a European project with the aim of identifying climate change impacts and suitable adaptation measures for the Mediterranean region (including Europe, North Africa and the Middle East).
Climate teleconnection: Teleconnection occurs when a local modification in climate conditions results in impacts (whether of a similar or different nature) in one or more other regions of the planet. For example, the El Nino Southern Oscillation is a major marine current that forms off the Peruvian coast in late winter, once or twice per decade. El Nino causes significant modifications to climate conditions worldwide.
Grid: In order to build a climate model, an imaginary grid is laid over the planet's surface. The grid resolution (which can be thought of as the distance between two cords in a fishing net) varies from several hundred kilometres to a few kilometres, depending on the model. The more closely-knit the grid, the higher the resolution of the model. However, because higher grid resolutions extend processing times, high-resolution models (known as regional models) can only be used for small geographic and time scales.
Forcing: To enable a model to operate, it must be supplied with input data for its constituent parameters (e.g. temperature, plant cover, atmospheric composition, etc.). A parameter is said to be "forced" if it is set manually, based on observations or the results of another model. In such cases, any feedback effects (involving the parameter in question) are ignored.
Coupling: Processes are modelled by producing computer code that translates the chemical and/or physical equations that characterize the process. It is possible to couple multiple models representing different processes (e.g. ocean, atmosphere, carbon cycle etc.), making them work together so that any interactions and feedback effects between the processes that occur naturally are taken into consideration.
Photochemistry: Involvement of light in a chemical reaction.
Research Scientist, LMD
philippe.drobinski @ lmd.polytechnique.fr