Precipitation response to Aerosol-Radiation and Aerosol-Cloud Interactions in Regional Climate Simulations over Europe

Abstract

Abstract. The effect of aerosols on regional climate simulations presents large uncertainties due to their complex and non-linear interactions with a wide variety of factors, including aerosol-radiation (ARI) and aerosol-cloud (ACI) interactions. These interactions are strongly conditioned by the meteorological situation and the type of aerosol. Despite increasing, there is nowadays a very limited number of studies covering this topic from a regional and climatic perspective. Hence, this contribution aims at quantifying the impacts on precipitation of the inclusion of ARI and ACI processes in regional climate simulations driven by ERA20C reanalysis. A series of regional climatic simulations (years 1991–2010) for the Euro-CORDEX domain have been conducted including ARI and ACI, establishing as reference a simulations where aerosols have not been included interactively (BASE). The results show that the effects of ARI and ACI on mean spatially averaged precipitation are limited. However, a spatial redistribution of precipitation occurs when introducing the ARI and ACI processes in the model; as well as some changes in the intensity precipitation regimes. The main differences with respect to the base-case simulations occur in central Europe, where a decrease in precipitation is associated with a depletion in the number of rainy days and low clouds. This reduction in precipitation presents a strong correlation with the ratio PM2.5/PM10, since the decrease is specially intense during those events with high values of that ratio (pointing to high levels of anthropogenic aerosols) over the aforementioned area. The precipitation decrease occurs for all ranges of precipitation rates. On the other hand, the model produces an increase in precipitation over the western Mediterranean basin associated with an increase of clouds and rainy days when ACI are implemented. Here the change is caused by the high presence of PM10 (low PM2.5/PM10 ratios, pointing to natural aerosols). In this case, the higher amount of precipitation affects only to those days with low rates of precipitation. Finally, there are some disperse areas were the inclusion of aerosols leads to an increase in precipitation, specially for moderate and high precipitation rates.

Climate Change and Weather Extremes in the Eastern Mediterranean and Middle East

“…Scattering and absorption of solar radiation by atmospheric aerosols (such as dust and soot from the burning of biomass and pollution) can modify the radiation budget, atmospheric stability, heat fluxes and thus affect cloud formation, microphysics (albedo, droplet size distribution, and lifetime) and precipitation. In this respect, several studies focused on the indirect climate implications of aerosols and trace gases via their effect on cloud properties and convective precipitation processes over the EMME region (Bougiatioti et al., 2016; Kallos et al., 2014; López‐Romero et al., 2021; Ramanathan et al., 2001; Rosenfeld et al., 2001; Solomos et al., 2011; Tang et al., 2018). On a global scale, desert dust exerts an estimated top of atmosphere (TOA) radiative forcing in the range of −0.6 to 0.4 Wm −2 , while in the EMME region, the forcing, both at the TOA and surface, is much more intense due to high surface reflectivity and enhanced aerosol loading, especially during the summer season (Alpert et al., 1998, 2005; Alpert & Kishcha, 2008).…”