Freshwater paradox: will saving of water help in mitigating climate change or increase the instability of the hydrological cycle?

The series of severe droughts in Europe from the beginning of this century may have a root cause to which we do not pay enough attention. The key function of the water cycle - energy, and water distribution - is directly influenced by climate change. Analyzing the trends of ERA5-Land gridded meteorological data for Central-Europe confirms significant trends with p=0.05 for temperature, relative humidity, and net radiation. Average increase of net radiation energy in Hungary is about 80mm in water equivalent during the last four decades. This increased load has an impact on the energy transfer processes where evapotranspiration has the largest share.

Trends of actual evaporation and Penman reference evaporation were analyzed in the study region. Evapotranspiration was estimated by the complementary relationship method of evaporation. Both parameters show significantly increasing trend. The warning signal, however, is that the gap between them is increasing, too. Demand (represented here by reference evaporation) is increasing faster than supply (evapotranspiration). Considering that water is the dominant energy transfer medium of climatic energy, an opening gap can be interpreted as the stability of the energy distribution system is decreasing. This change can trigger a growing risk of droughts, where drought is a symptom of system underperformance.

The common interpretation of evaporation as a loss factor in the hydrological cycle should be urgently changed to a functional view: energy distribution via evaporation is a vital environmental service. Atmospheric circulation and the water cycle are inherently connected. Saving water may not be the correct approach to mitigate climate change, as it only amplifies the deficiencies of the energy exchange process. One cannot stop desertification by chasing water use efficiency and using less water, but the other way around: scarcity of water can only be eliminated by ensuring that a wealth of water resources is available for evapotranspiration, thus for smooth distribution of climatic energy.