Evaporation trends in Spain: a comparison of Class A pan and Piché atmometer measurements

Abstract

Interest is growing in the trends of atmospheric evaporation demand, increasing the need for long-term time series. This work describes, for the first time, the development of a dataset on evaporation in Spain based on long-term series of Piché and pan measurement records. Piché measurements have been reported for > 50 stations since the 1960s. Measurements of pan evaporation, which is a much more widely studied variable in the literature, are also available, but only since 1984 for 21 stations. Particular emphasis was placed on the homogenization of this dataset. Both the mean annual Piché and pan series over Spain showed evaporative increases during the common study period (1985−2011), by a rate of around + 0.1 mm d −1 decade −1. Furthermore, using the annual Piché records since the 1960s, an evaporation decline was detected from the 1960s to the mid-1980s, which resulted in a non-significant trend over the entire 1961−2011 period. Our results indicate agreement between the decadal variability of reference evapotranspiration and the surface solar radiation previously reported and the evaporation from Piché and pan measurements, especially during summer. The suitability of Piché records compared to pan evaporation data to represent past trends is discussed. KEY WORDS: Piché evaporimeter · Pan evaporation · Trends · SpainResale or republication not permitted without written consent of the publisher Clim Res 61: [277][278][279][280][281][282][283][284][285][286][287][288] 2014

Comparison of five different methods in estimating reference evapotranspiration in Cape Coast, Ghana

“…The underestimation partly could be due to lack of sufficient wind in the Stevenson's screen that was shielding the evaporimeter Sanchez-Lorenzo et al (2014). These underestimations of the ETo results were similar to those of Diop et al (2015), but different from those of Knox et al (2011) who observed overestimation of ETo relative to FAO56-PM.…”

“…However, the Class A pan had the least MAE and MAPE (0.26 mm day -1 and 6.5% respectively) relative to the Piche evaporimeter and even among all the methods. The difference in their correlation coefficients and the errors could be due to the fact that the Piche evaporimeter was shielded from solar radiation and its measurement could not be directly affected by the radiative parameters controlling ETo which was not the case for the Class A pan which was in the open as intimated by Sanchez-Lorenzo et al (2014).…”

“…The standard Class A pan, developed by the US Weather Bureau was used for the study. The pan was a spherical tank of galvanized iron, with a diameter around 120 cm and was 25 cm deep, and mounted on a wooden platform (Sanchez-Lorenzo et al, 2014). The pan was filled with water to about 5 cm below the rim and the daily fall of the water level was manually measured every morning at 0900 h, refilling the water level if needed or reducing the content of water if rain had caused the tank to overflow (WMO, 2008).…”

Reference crop evapotranspiration database in Spain (1961–2014)

“…The use of methods for calculating ET o requiring only temperature data, such as the Thornthwaite (Thornthwaite, 1948) or Hargreaves (Hargreaves and Samani, 1985) approaches, are still common, especially because temperature is commonly available, and temperature and solar radiation accounts for 80 % of the ET o variability (Mendicino and Senatore, 2013;Samani, 2000). One of the major drawbacks of these methods is that variability and trends in the estimated ET o values depend only on temperature, regardless of the importance of the other variables (Irmak et al, 2012;McVicar et al, 2012;Sheffield et al, 2012;Tomas-Burguera et al, 2017).…”

An updated review on recent trends in observational surface atmospheric variables and their extremes over Spain

“…They also found that ETo trends were mainly explained by the decrease in relative humidity and the increase in maximum temperature since the 1960s, particularly during summer months. Sánchez-Lorenzo et al (2014) developed, for the first time, an evaporation dataset for Spain based on long-term series of Piché atmometer and pan measurement records. Both the mean annual Piché and pan series showed evaporative increases over Spain during the study period (1985−2011).…”