Autour des relations température-précipitations dans la région Euro-Méditerranéenne

Abstract : The study of the water cycle is of crucial importance for all societies and more particularly for those around the Mediterranean which suffer both from droughts in summer and floods due to extreme precipitation events occurring in the autumn and in winter. Temperature is one of the main factors that govern the maximum intensity of precipitation through the Clausius-Clapeyron (CC) relationship. This law expresses the maximum amount of water vapor that the atmosphere can contain at a given temperature. Using regional climate simulations and observations, we have shown that the temperature-precipitation extremes relationships of the Mediterranean basin have a hooked shape with an increase in extreme precipitation near CC at low temperatures and then a smaller increase (or even a decrease) at higher temperatures. Aerosols, which are present in large quantities around the Mediterranean, absorb and reflect part of the radiation, helping to cool the lower layers of the atmosphere. By their action on the surface temperature, aerosols reduce precipitation. The study of numerical simulations also shows a modification of the temperature-precipitation relationship by aerosols (their effect on clouds) in the Euro-Mediterranean region. In addition to the lowering the available water vapor content, aerosols stabilize the atmosphere by further cooling the lower layers of the atmosphere relatively to the upper layers. The temperature-precipitation relationship of a given climate is often studied in order to predict precipitation trends in a warmer future climate. However, this extrapolation assumes that the relationship between temperature and precipitation does not change between the present climate and the future climate, a hypothesis which proves to be fragile when looking at the sensitivity of this relationship to the aerosol content of the atmosphere, but also in view of the change in the availability of water vapor in a future climate. In this thesis, we have shown that for several coastal stations, projections in the future of several regional climate models suggest that extreme precipitation should increase in proportion to the temperature increases according to CC law. A phenomenon that we have not been able to observe for more isolated areas from the sea and where the influx of water vapor would be reduced.
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Nicolas da Silva. Autour des relations température-précipitations dans la région Euro-Méditerranéenne. Climatologie. Université Paris-Saclay, 2018. Français. ⟨NNT : 2018SACLX069⟩. ⟨tel-02059296⟩

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