Temporal evolution of surface humidity in Spain: Recent trends and possible physical mechanisms

We analyzed the evolution of surface relative humidity (RH) and specific humidity (q) in Spain, based on complete records available from the State Meteorological Agency of Spain. The surface RH records used span the period 1920-2011, but because of spatial and temporal constraints in the dataset we used a subset of the data, covering the period 1961-2011. The subset contained 50 monthly series of RH, which were created through a process of quality control, reconstruction and homogenization. The data shows that there was a large decrease in RH over mainland Spain from 1961 to 2011, which was greatest in spring and summer. In contrast, there was no overall change in the specific humidity in this period, except in spring, when an increase was observed. The decrease in RH affected the entire country, but the changes in specific humidity were less homogeneous. For specific humidity there was a general increase in the northern and eastern parts of Spain, whereas negative trends dominated in the central and southern areas, mainly during the summer months. The results suggest that an increase in the water holding capacity of the atmosphere as a consequence of warming during recent decades has not been accompanied by an increase in the surface water vapor content, probably because the supply of water vapor from the main terrestrial and oceanic areas has been constrained. We discuss the implications of these findings for evapotranspiration processes, precipitation and water management in Spain. © 2013 Springer-Verlag Berlin Heidelberg.The authors are grateful to J. C. González-Hidalgo for his helpful comments on the first draft of this article. We would like to thank the Spanish Meteorological State Agency (AEMET) for providing the database used in this study. This work has been supported by the research projects CGL2011-27574-CO2-02 and CGL2011-27536 financed by the Spanish Commission of Science and Technology and FEDER, “Demonstration and validation of innovative methodology for regional climate change adaptation in the Mediterranean area (LIFE MEDACC)” financed by the LIFE programme of the European Commission and CTTP1/12 “Creación de un modelo de alta resolución espacial para cuantificar la esquiabilidad y la afluencia turística en el Pirineo bajo distintos escenarios de cambio climático”, financed by the Comunidad de Trabajo de los Pirineos. The second author was granted by the postdoctoral JAE-DOC043 (CSIC) and JCI-2011-10263 (Spanish Ministry of Science and Innovation) grants. The third author was supported by a postdoctoral fellowship from the “Secretaria per a Universitats i Recerca del Departament d’Economia i Coneixement, de la Generalitat de Catalunya i del programa Cofund de les Accions Marie Curie del 7è Programa marc d’R+D de la Unió Europea” (2011 BP-B 00078).Peer Reviewe