High-resolution projections of climate change over the Iberian Peninsula using a mesoscale model

Global projections of climate indicate that substantial changes might occur in the future as a consequence of global warming. Such changes would have important environmental, social and economical implications. However, the climate response to global warming strongly varies from region to region and thus it requires to be studied at scales that General Circulation Models (GCMs) cannot resolve. In this Thesis, the Weather Research and Forecasting (WRF) model was selected to downscale GCMs information and generate physically-consistent highresolution projections of climate change scenarios over the Iberian Peninsula (IP). A set of climate simulations over the IP were performed at 10-km resolution to explore the impact of global warming on precipitation and temperature at regional scales. At this spatial resolution, the model is able to incorporate the e↵ects of topographical features that are know be key factors in the spatial distribution of the climate regimes and the areas within the IP that might be subjected to di↵erent changes can be identified. Particular attention was paid to the model configuration and its evaluation with respect to the present climate. Initially, eight decadal (1990-1999) simulations were completed to conduct a sensitivity test and determine which combination of physics options better describe the Iberian climate features. The model outputs were compared with observations using an objective multi-step regionalization technique to circumvent the spatial scale disparity between the model estimates and the site-specific observations. No combination was found to outperforms the others under all circumstances and not all the physics schemes were found to be equally decisive. In fact, a compromise solution had to be selected bearing in mind factors such as the performance with respect to the di↵erent variables in the di↵erent regions, or the benefit gained with higher-complexity schemes. The model evaluation consisted in the assessment of the model ability to simulate present climate in terms of precipitation and temperature using the Spain02 gridded dataset to compare with. Three di↵erent present climate (1970-1999) simulations driven by three boundary data (ERA-40, ECHAM5 and CCSM3.0) covering the entire IP were completed to elucidate whether the model is suitable to study the Iberian climate. The validation reveals that, in spite of some nonnegligible errors, the model is able to reproduce most of the main features of the Iberian precipitation and temperature. In particular, WRF shows particularly good agreement with the observations in terms of the probability distributions and the upper-percentiles. Finally, the high-resolution climate change projections were obtained from an ensemble of future climate (2070-2099) simulations over the IP. In particular, three emissions scenarios (B1, A1B and A2) and two GCMs (ECHAM5 and CCSM3.0) were employed to reduce the uncertainty associated to the boundary conditions. The model estimates for temperature and precipitation were compared with those from the present climate simulations and the projected changes were analyzed. Not only the long-term means were examined, but also the highorder statistics, including di↵erent extreme indices to characterize the tails of the distributions. The high-resolution projections of climate change scenarios over the Iberian Peninsula suggests that substantial decreases in mean precipitation might be expected over IP, but their magnitude is projected to be unevenly distributed across the IP. However, the precipitation extremes events might not be overall expected to change significantly. On the other hand, temperature increases are very likely to occur over the entire IP, particularly for maximum temperature extremes. The most a↵ected areas by precipitation changes are projected to be the mountainous regions, whereas those a↵ected by temperature increases cover large areas in the interior of the IP. This Thesis represents a valuable contribution to the understanding of global warming repercussions on the Iberian climate. The spatial resolution employed in the simulations enabled the generation of climate change projections with a degree of detail that is unprecedented in the Iberian Peninsula. Furthermore, this study provides a comprehensive description of the projected changes at very di↵erent timescales, including the extreme events, which might be of greater impact than the mean climatic changes.