*Review* **Evapotranspiration Trends and Interactions in Light of the Anthropogenic Footprint and the Climate Crisis: A Review**

**Stavroula Dimitriadou and Konstantinos G. Nikolakopoulos \***

Department of Geology, University of Patras, 26504 Rion, Greece; sdhm@upatras.gr

**\*** Correspondence: knikolakop@upatras.gr; Tel.: +30-261-099-759-2

**Abstract:** Evapotranspiration (ET) is a parameter of major importance participating in both hydrological cycle and surface energy balance. Trends of ET are discussed along with the dependence of evaporation to key environmental variables. The evaporation paradox can be approached via natural phenomena aggravated by anthropogenic impact. ET appears as one of the most affected parameters by human activities. Complex hydrological processes are governed by local environmental conditions thus generalizations are difficult. However, in some settings, common hydrological interactions could be detected. Mediterranean climate regions (MCRs) appear vulnerability to the foreseen increase in ET, aggravated by precipitation shifting and air temperature warming, whereas in tropical forests its role is rather beneficial. ET determines groundwater level and quality. Groundwater level appeared to be a robust predictor of annual ET for peatlands in Southeast Asia. In semi-arid to arid areas, increases in ET have implications on water availability and soil salinization. ET-changes after a wildfire can be substantial for groundwater recharge if a canopy-loss threshold is surpassed. Those consequences are site-specific. Post-fire ET rebound seems climate and fire-severity-dependent. Overall, this qualitative structured review sets the foundations for interdisciplinary researchers and water managers to deploy ET as a means to address challenging environmental issues such as water availability.

**Keywords:** actual evapotranspiration; potential evapotranspiration; reference evapotranspiration; evaporation; evaporation paradox; global dimming; wind stilling; forest fires; groundwater

## **1. Introduction**

The importance of evapotranspiration (ET) is demonstrated by its participation in the hydrological cycle (as a hydrological process) and in the surface energy balance (as a flux) [1]. Taking into account that a high percentage of the precipitated water is evaporated and transpired (e.g., 65% Ireland [2]; 62% Greece [3]) it is obvious that water budgets are dictated by the fluctuations of ET and subsequently by the dependency of ET on several environmental parameters [4–6]. ET according to researchers is a component that is not perfectly understood yet. Thus, it should be thoroughly studied as a major key parameter involving numerous mechanisms, mediating fluctuations of other variables, and controlling processes or causing considerable problems after intense disturbances by human activity or climate change.
