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 type of aerosol, but, despite their increase, only a limited number of studies have covered this topic from a regional and climatic perspective. This contribution thus aims to quantify 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 (for the period 1991–2010) for the Euro-CORDEX domain were conducted including ARI and ARI + ACI (ARCI), establishing as a reference a simulation where aerosols were not included interactively (BASE). The results show that the effects of ARI and ACI on time-mean spatially averaged precipitation over the whole domain are limited. However, a spatial redistribution of precipitation occurs when the ARI and ACI processes are introduced into the model, as well do changes in the precipitation intensity 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 clouds at low level (CLL). This reduction in precipitation presents a strong correlation with the ratio PM2.5∕PM10, since the decrease is especially intense during those events with high values of that ratio (pointing to high levels of anthropogenic aerosols) over central Europe. The precipitation decrease occurs for all ranges of precipitation rates. On the other hand, the model produces an increase in precipitation over the eastern Mediterranean basin associated with an increase in clouds and rainy days when ACIs 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 days with low rates of precipitation. Finally, there are some disperse areas where the inclusion of aerosols leads to an increase in precipitation, especially for moderate and high precipitation rates.
Highlights
The importance of atmospheric aerosols has multiple aspects, all of great scientific and socioeconomic relevance
The sensitivity of precipitation to the aerosol treatment in climate simulations is analyzed by comparing BASE, ARI and ARCI simulations over Europe over a 20-year period
This reduction in precipitation is linked mainly to a reduction in the number of days with precipitation > 0.1 mm (Np01) and clouds at low level (CLL); the most significant and widespread changes are obtained for CLL
Summary
The importance of atmospheric aerosols has multiple aspects, all of great scientific and socioeconomic relevance. The World Health Organization (WHO, 2013) has recognized that the degradation of air quality by atmospheric aerosols is a threat to human health. The Fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate Change (IPCC) points to atmospheric aerosols as one of the main sources of uncertainty in current climate simulations (Boucher et al, 2013). Myhre et al (2013) indicate that the uncertainty in the radiative forcing produced by aerosols greatly exceeds that of all other forcing mechanisms combined. Despite the increasing number of articles published on the interactions between aerosols and climate over the last. López-Romero et al.: Precipitation response to ARI and ARCI over Europe
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