Projected hydrologic changes over the north of the Iberian Peninsula using a Euro-CORDEX multi-model ensemble.

This study explores the impacts of climate change on the hydrology of the headwater areas of the Duero River Basin, the largest basin of the Iberian Peninsula. To this end, an ensemble of 18 Euro-CORDEX model experiments was gathered for two periods, 1975-2005 and 2021-2100, under two Representative Concentration Pathways (RCP4.5 and RCP8.5), and were used as the meteorological forcings of the Variable Infiltration Capacity (VIC) during the hydrological modelling exercise. The projected hydrologic changes for the future period were analyzed at annual and seasonal scales using several evaluation metrics, such as the delta changes of the atmospheric and land variables, the runoff and evapotranspiration ratios of the overall water balance, the snowmelt contribution to the total streamflow and the centroid position for the daily hydrograph of the average hydrologic year. Annual streamflow reductions of up to 40% were attained in various parts of the basin for the period 2071-2100 under the RCP8.5 scenario, and resulted from the precipitation decreases in the southern subwatersheds and the combined effect of the precipitation decreases and evapotranspiration increases in the north. The runoff and the evapotranspiration ratios evinced a tendency towards an evaporative regime in the north part of the basin and a strengthening of the evaporative response in the south. Seasonal streamflow changes were mostly negative and dependent on the season considered, with greater detriments in spring and summer, and less intense ones in autumn and winter. The snowmelt contribution to the total streamflow was strongly diminished with decreases reaching -80% in autumn and spring, thus pointing to a change in the snow regime for the Duero mountains. Finally, the annual and seasonal changes of the centroid position accounted for the shape changes of the hydrograph, constituting a measure of seasonality and reflecting high correlations degrees with the streamflow delta changes.

Projected changes in the Iberian Peninsula drought characteristics.

High spatial resolution drought projections for the Iberian Peninsula (IP) have been examined in terms of duration, frequency, and severity of drought events. For this end, a set of regional climate simulations was completed using the Weather Research and Forecasting (WRF) model driven by two global climate models (GCMs), the CCSM4 and the MPI-ESM-LR, for a near (2021-2050) and a far (2071-2100) future, and under two representative concentration pathway (RCP) scenarios (RCP4.5 and RCP8.5). Projected changes for these simulations were analyzed using two drought indices, the Standardized Precipitation Evapotranspiration Index (SPEI) and the Standardized Precipitation Index (SPI), considering different time scales (3- and 12-months). The results showed that the IP is very likely to undergo longer and more severe drought events. Substantial changes in drought parameters (i.e., frequency, duration, and severity) were projected by both indices and at both time scales in most of the IP. These changes are particularly strong by the end of the century under RCP8.5. Meanwhile, the intensification of drought conditions is expected to be more moderate for the near future. However, the results also indicated key differences between indices. Projected drought conditions by using the SPEI showed more severe increases in drought events than those from SPI by the end of the century and, especially, for the high-emission scenario. The most extreme conditions were projected in terms of the duration of the events. Specifically, results from the 12-month SPEI analysis suggested a significant risk of megadrought events (drought events longer than 15 years) in many areas of IP by the end of the century under RCP8.5.

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 21st 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.