Analysis of evaporation from water surface measured automatically by the EWM evaporimeter at the weather station in Ústí nad Orlicí between 2001 and 2014

Abstract

Evaporation from water surface at the station in Ústí nad Orlicí was measured using an automatic EWM evaporimeter. The analysed period was from May 1st to September 30th in the years 2001 to 2014. Statistical analysis of the daily evaporation showed that the values ranged between 0.0 mm and 7.3 mm (July 17, 2007). This maximum value was analysed in detail and considered to be realistic based on the unusual weather conditions on that day. The highest average daily evaporation was observed in July (2.8 mm), followed by August (2.5 mm). On the other hand the lowest average daily evaporation was found to be in September (1.6 mm). Average monthly evaporation totals in the analysed period (2001–2014) ranged from 49.1 mm (September) to 86.1 mm (July). The absolute lowest monthly evaporation total in the analysed period was measured in September 2002 (34.4 mm), on the other end of the scale, the absolute highest monthly evaporation in the period of interest was measured in August 2003 (114.5 mm). Statistics of annual data show that out of the 14 years analysed, the lowest evaporation was observed in 2005 (263.5 mm), while the highest in 2007 (426.1 mm). Average annual (May-September) evaporation for the 14 years is 355.0 mm. The trend in evaporation for May and August is negative, in the other months it is positive. The largest change was seen in July, where the linear index value is +1.555. However, the trends in monthly values are not statistically significant.