Widening Gap of Land Evaporation to Reference Evapotranspiration Implies Increasing Vulnerability to Droughts in Hungary

Abstract

Severe droughts of 2022 in Europe raise the question if one has sufficient knowledge and tools to predict and prevent such events. Analysis of 40 years of meteorological data for Hungary between 1981 and 2020 confirms significant upward trends with p = 0.05 in temperature, relative humidity, and net radiation. Shortwave net radiation has increased by 89.6 mm in water equivalent. Estimates of land evaporation and reference evapotranspiration also show a significantly increasing trend. The gap between them is widening with a significant trend in northeast Hungary. The demand (reference evapotranspiration) is increasing by 2.23 ± 0.3 mm yr^–1, while supply (land evaporation) by 1.64 ± 0.2 mm yr^–1. The opening gap can be interpreted as a decreasing stability of the energy distribution system, where water is the dominant energy transfer medium for climatic energy. This change could lead to an increased risk of droughts, a symptom of system underperformance. The climatic energy distribution process – a key environmental service - is shifting to a new operating point where more water would be needed to transport energy. These trends call for a process capability approach. Desertification cannot be stopped by chasing water use efficiency and using less water, but vice versa: water scarcity can only be eliminated by ensuring that there is sufficient water available for evapotranspiration. This will raise the priority for initiatives to design and implement a wide range of preventing actions, such as nature-based solutions and water retention measures.