Aerosol Direct Radiative Impacts on the regional climate in the MEDiterranean region. – ADRIMED

The general goal of project ADRIMED is to assess the impacts of the direct radiative effect of aerosols from various origins on the regional climate of the Mediterranean region. The main focus is to verify to which extent feedbacks from (1) the decrease in surface solar radiation that decreases evaporation, and (2) the increase in solar absorption in the column that increases atmospheric heating; reinforce the drought that characterizes the long Mediterranean summer season and might amplify the large
regional precipitation decrease predicted by all IPCC climate models in the context of global warming. The Mediterranean climate can be considered as a prototype of the future warm conditions that are predicted to prevail in many areas of Europe. The Mediterranean region has also been identified as one of the most prominent “Hot-Spots” in future climate change projections with a substantial precipitation decrease and warming, especially in the warm and dry season. At this time, most of the global and regional climate simulations have only investigated the impact of global warming on the water resources over the Med. region without considering the possible influence of various natural and anthropogenic aerosols that significantly modify the Med. radiative budget, especially during the long dry season when high aerosols concentrations and clear sky conditions are common.

The project strategy is based on an integrated approach combining an intensive experimental field campaign and spaceborne observations, radiative transfer, and climate modelling with regional climate models particularly adapted to capture the high complexity of the Mediterranean region. In particular, we propose a summer field experiment in summer 2012, unprecedented in the western Mediterranean, based on in situ and remote sensing observations from surface super-sites and the French ATR-42 research aircraft. This will result in an original database of the physical, chemical, and optical properties and direct radiative impact of the main aerosol types and their vertical distribution in the Mediterranean tropospheric column. A focus will be put on improving knowledge of absorption properties of the various aerosol types following their major influence on the radiative impact, and their large variability. These experimental observations will be used in detailed 1D radiative transfer simulations for assessing the direct and semi-direct radiative forcing from various particle sources over the basin. The database will also allow us significantly improving the parameterizations of aerosols in the Regional Climate Model RegCM4.

In a first step, such an improved model will be used to estimate the aerosol optical properties at the regional scale and the associated direct radiative forcing over the basin with a focus on its impact on surface evaporation and atmospheric heating. Secondly, feedbacks of such forcings on the Med. climate and more specifically on the water budget, will be investigated by using RegCM4 regional climate simulations. Simulations will be conducted first for present climate conditions (1990-2010). In a second phase, the same kind of simulations will be carried out using future climate boundary forcing provided by IPCC climate change and emission scenarios (2030-2070). This should give us insights on the likely evolution of aerosol forcing and impacts in a changing (and likely drier) Mediterranean environment. Although each season will be investigated, a particular attention will be made on the dry season.