Future changes in land and atmospheric variables: An analysis of their couplings in the Iberian Peninsula

This work investigates climate-change projections over a transitional region between dry and wet climates, the Iberian Peninsula (IP). With this purpose, the Weather Research and Forecasting (WRF) model, driven by two global climate models (CCSM4 and MPI-ESM-LR) previously bias-corrected, was used to generate high-resolution climate information. Simulations were carried out for two periods, 1980-2014 and 2071-2100, and under two representative concentration pathways (RCP4.5 and RCP8.5). The analysis focused on changes in land-surface processes, their causes, and the potential impact on the climate system. To achieve this, seasonal projected changes of land-surface (soil moisture and surface evapotranspiration) and atmospheric variables involved in the hydrologic (i.e., precipitation and runoff) and energy balance (i.e., temperature and solar incoming radiation) were investigated. The results reveal that the IP is likely to experience a soil dryness by the end of the 21^st century, particularly during summer and fall, more apparent in the southern IP, and stronger under the RCP8.5. However, such trends would have different implications throughout the year and directly affect the surface evapotranspiration. Moreover, soil-drying trends are mainly associated with reductions in the large-scale precipitation during spring, summer, and fall and by enhanced evapotranspiration particularly in spring over the northwestern IP. In addition, the results show notably changes in soil conditions at high altitude, particularly during winter, which may alter the land-atmosphere processes that currently occur in these regions. In this context, noteworthy changes in the climate system are expected, leading to adverse impacts on water resources and temperature. The results highlight the complex and nonlinear nature of land-atmosphere interactions in regions such as the IP, which is a tremendous challenge for adequately developing mitigation and adaptation strategies to anthropogenic climate change.