Precipitation over coastal regions of southern France and its impacts on the regional hydrological cycle

The hydrological cycle over southern France is an interplay between highly variable precipitation impacting the variability of soil moisture and continental runoff. The regional hydrological cycle experiences strong impacts of the Mediterranean Sea (Gulf of Lion) through the moisture advection. Moreover, the strong coupling between the atmosphere and the land surface is affecting all branches of the regional hydrological cycle, especially due to the specific structure of the orography in the region. Under the climate change scenarios potential intensification of the regional hydrological cycle, resulting in extreme hydroclimate events is a critically important phenomenon for understanding mechanisms of climate variability over the Mediterranean.

We perform the analysis of long-term daily precipitation time series over southern France (300 stations from METEO-FRANCE collection) along with modern era Reanalysis (ERA5, JRA55) and satellite datasets (TRMM, GPCP, and Persian) over the period from 1979  onwards. Diagnostics estimate linear trends and interannual variability in precipitation totals and precipitation extremes and allow for quantifying the differences in precipitation variability patterns across the different datasets, demonstrating their strengths and weaknesses. Then we associated changes in precipitation with tendencies in soil moisture derived from the GLEAM-GRACE datasets, thus quantifying regional responses of soil moisture to precipitation impacts. Finally, we analyze the representation of the observed regional hydrological cycle in historical simulations with regional (Euro-CORDEX) and global (CMIP6) climate models. We, thus, establish a statistical association between precipitation, soil moisture, and continental runoff and quantify the role of regional atmospheric circulation in forming multidecadal changes in the regional hydrological cycle.