Climatic influence on atmospheric evaporative demand in Estonia (1951-2015)

Atmospheric evaporative demand (ADE) trends at global scale are important to understand the impact of global warming in the hydrological cycle. But there is no consensus, in the global scale studies, about ADE variability and many areas have been ignored in regional studies. This is the case of Estonia, located in the eastern coast of the Baltic Sea between 57.5 and 59.5°N. To shed light on the ADE variability in the country we have studied the spatial and temporal variability of ET₀ from 1951 to 2015.

We have computed ET₀ from 9 high-quality meteorological stations by Penman–Monteith equation. We have analysed the spatial and temporal variability of ET₀ and its main drivers i.e. maximum temperature, minimum temperature, wind speed, sunshine duration, relative humidity and atmospheric pressure.

ET₀, at annual scale and country level, shows a positive and significant trend with a magnitude of change during the studied period of 5.3 mm decade^-1, with the highest values during the spring (4.1 mm decade^-1).  The costal series show a higher magnitude of change (7.1 mm decade^-1in average) than the inland series (4.3 mm decade^-1 in average), principally because coastal areas show greater magnitude of change during the summer. High significant correlation (r=0.7-0.8) have been found among computed ET₀ and observed evaporation measurements with evaporation pan and lysimeter during the period 1968-2005.

At annual scale, during spring and summer ET₀ is highly correlated with sunshine (positive), relative humidity (negative) and maximum temperature (positive). Meanwhile sunshine has no significate trend, maximum temperature shows positive and significant trend in all the series and seasons and relative humidity shows significant negative trends in 8 of the 9 series studied during the spring.