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In 2015, a new automatic weather station (AWS) was installed in a high elevation site in Gredos mountains (Central System, Spain). Since then, a surprisingly high number of heavy precipitation events have been recorded (55 days with precipitation over 50 mm, and a maximum daily precipitation of 446.9 mm), making this site a hotspot in Spain in terms of annual precipitation (2177 mm year) and extreme precipitation events. The neighboring stations available in the region with longer data series, including the closest ones, already informed of wet conditions in the area, but not comparable with such anomaly behavior detected in the new station (51% higher). In this study, we present the temporal variability of detected heavy precipitation events in this mountain area, and its narrow relation with atmospheric patterns over the Iberian Peninsula. Results revealed that 65% of the events occurred during advections from West, Southwest, South and cyclonic situations. A regression analysis showed that the precipitation anomaly is mostly explained by the location windward to the Atlantic wet air masses and the elevation. However, the variance explained by the models is rather low (average R2 for all events > 50 mm is 0.21). The regression models underestimate on average a 60% intensity of rainfall events. Oppositely, the high-resolution weather forecast model AROME at 0.025° was able to point out the extraordinary character of precipitation at this site, and the underestimation of observed precipitation in the AWS was about 26%. This result strongly suggests the usefulness of weather models to improve the knowledge of climatic extremes over large areas, and to improve the design of currently available observational networks. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Summary We analyzed the spatio-temporal evolution of evaporation observations from Piché atmometers (1961–2011; 56 stations) and Pan evaporimeters (1984–2011; 21 stations) across Spain, and compared both measurements with evaporation estimates obtained by four physical models: i.e., Food and Agricultural Organization-56 Penman–Monteith, Food and Agricultural Organization-Pan, PenPan and Penman, based on climate data. In this study we observed a positive and statistically significant correlation between Piché and Pan evaporation measurements during the common period (1984–2011; 19 stations), mainly in summer. When evaporation observations and estimates were compared, we detected positive and statistically significant correlations with the four methods, except for winter. Among the four physical models, the FAO-Pan showed the best fitting to both Piché and Pan evaporation measurements; the PenPan model overestimated evaporation rates; and the FAO-Penman–Monteith and Penman methods underestimated evaporation observations. We also observed a better spatial agreement between Pan evaporation and estimates than that obtained by Piché measurements. Annual and seasonal trends of evaporation estimates show a statistically significant increase for 1961–2011, which do not agree with long-term Piché evaporation trends; e.g. a discontinuity was found around the 1980s. Radiative and aerodynamic driving factors suggest that this discontinuity, and the observed evaporation trends across Spain could be associated with the abrupt increase in air temperature observed during last few decades (i.e., global warming). Further investigations using available Piché evaporation observations for other regions are needed to better understand physical components influencing long-term trends of evaporation. [ABSTRACT FROM AUTHOR]

In this study we analyzed the spatial distribution, temporal variability and trends in reference evapotranspiration (ET0) in Spain from 1961 to 2011. Twelve methods were analyzed to quantify ET0 from quality controlled and homogeneous series of various meteorological variables measured at 46 meteorological stations. Some of the models used are temperature based (e.g., Thornthwaite, Hargreaves, Linacre), whereas others are more complex and require more meteorological variables for calculation (e.g., Priestley-Taylor, Papadakis, FAO-Blaney-Criddle). The Penman-Monteith equation was used as a reference to quantify ET0, and for comparison among the other methods applied in the study. No major differences in the spatial distribution of the average ET0 were evident among the various methods. At annual and seasonal scales some of the ET0 methods requiring only temperature data for calculation provided better results than more complex methods requiring more variables. Among them the Hargreaves (HG) equation provided the best results, at both the annual and seasonal scales. The analysis of the temporal variability and trends in the magnitude of ET0 indicated that all methods show a marked increase in ET0 at the seasonal and annual time scales. Nevertheless, results obtained suggested substantial uncertainties among the methods assessed to determine ET0 changes, due to differences in temporal variability of the resulting time series, but mainly for the differences in the magnitude of change of ET0 and its spatial distribution. This suggests that ET0 trends obtained by means of methods that only require temperature data for ET0 calculations should be evaluated carefully under the current global warming scenario. [ABSTRACT FROM AUTHOR]