Precipitation Recycling: Moisture Sources over Europe using ERA-40 Data

Atmospheric moisture within a region is supplied by both local evaporation and advected from external sources. The contribution of local evaporation in a region to the precipitation in the same region is defined as "precipitation recycling." Precipitation recycling helps in defining the role of land-atmosphere interactions in regional climate. A dynamic precipitation recycling model, which includes the moisture storage term, has been applied to calculate summer variability of the precipitation recycling over Europe based on 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) data. Time series for three subregions in Europe (central Europe, the Balkans, and Spain) are obtained to analyze the variability in recycling and to compare the potential in the subregions for interactions between land surface and atmospheric processes. In addition, the recycled precipitation and recycling ratios are linked to several components of the water vapor balance equation [precipitation, evaporation, precipitation minus evaporation (P - E), and moisture transport]. It is found that precipitation recycling is large in dry summers for central Europe, while the opposite is true for the Balkans. Large precipitation recycling is determined in relation with weak moisture transport and high evaporation rates in central Europe. This occurs for dry summers. For the Balkans, precipitation recycling is large in wet summers when moisture transport is weak, and P - E and evaporation are large. Here, the recycling process intensifies the hydrological cycle due to a positive feedback via convective precipitation and therefore the amount of recycled precipitation is larger. For Spain, recycling is also larger when moisture transport is weak, but other correlations are not found. For regions such as central Europe in dry summers and the Balkans in wet summers, which are susceptible to land-atmosphere interactions, future climate and/or land use can have an impact on the regional climate conditions due to changes in evaporation.