Evolution of extreme summer precipitation patterns in the western Mediterranean basin

The precipitation at the Mediterranean coast of the Iberian Peninsula is strongly seasonal and presents a non-uniform spatial distribution due to complex topography. Summer is generally dry and rainfall is mainly produced by orographically-induced convective precipitation (commonly known as summer storms) generated over the mountain ranges of the basin. Projections of future climate change indicate a generalized reduction of both mean precipitation and summer storms over eastern Spain. Summer storms play a key role in the local climate and the hydrological cycle since they are fundamental for the region water resources and ecosystems providing necessary precipitation during the driest season of the year.

In this study, an extensive analysis of precipitation spatio-temporal patterns during summer, with special focus on summer storms, is conducted over the Hydrographic Confederations of the Júcar (CHJ) and Segura (CHS) located in the southeastern part of the Iberian Peninsula. Specifically, the Spain02 precipitation dataset, covering the period 1951-2019 in a daily base with a 5-km horizontal resolution, is used to analyze extreme precipitation and dry days trends over the study area, as well as at a more local scale regarding the river basins that conform the CHJ and CHS. In addition, the last two decades are analyzed using a disaggregation of precipitation events regarding its origin and development: (A) Atlantic advection, (B) summer storms and (C) Mediterranean advection. Besides, high-resolution simulations (about 3km), performed with the COSMO mesoscale model, will provide further information with respect to the influence of summer storms on the local climate and the hydrological cycle.

Contrarily to the negative tendency in number of summer storms and precipitation amount observed during the period 1951-2019 for summer, preliminary results show an increase in the number of these particular events in both CHJ and CHS during the late summer (August and September) for the last two decades along with a slightly increasing precipitation trend. In our discussion we will describe in detail the observed changes in the precipitation field in combination with changes in other water cycle components, such as soil moisture, and evaporation and the potential implications for the affected regions.