Evapotranspiration of an Abandoned Grassland in the Italian Alps: Influence of Local Topography, Intra- and Inter-Annual Variability and Environmental Drivers

Abstract

Evapotranspiration is a key variable of the hydrological cycle but poorly studied in Alpine ecosystems. The current study aimed to characterise the impact of topography and temporal variability on actual evapotranspiration (ETa) and its environmental drivers at an Alpine abandoned grassland encroached by shrubs on a steep slope. Eddy covariance, meteorological, hydrological and soil data were analysed over four growing seasons, of which two had wet and two dry conditions. The topography caused a systematic morning inflexion of ETa in all growing seasons, reflecting the valley wind system. Inter-annual differences of ETa exceeded 100 mm, and ETa means and cumulative values were significantly different between wet and dry growing seasons in the four years. Besides, ETa had a larger temporal variability in wet growing seasons. A bimodality of ETa was found in all years, caused by the onset of plant activity in the morning hours. Energy- and water-limited ETa periods were identified by comparing ETa to potential evapotranspiration (ETo). Periods of fifteen days revealed the main intra- and inter-annual differences of the environmental variables (air temperature, vapour pressure deficit—VPD, precipitation and ETa). The fixed effects of a linear mixed model based on ETa drivers explained 56% of ETa variance. The most important ETa drivers were net radiation and VPD, followed by wind speed. In growing seasons characterised by dry conditions, air temperature and the ground heat flux at the surface (either both or one of them) influenced ETa as well. The current study contributed to the understanding of topographical and temporal effects on evapotranspiration and other micrometeorological variables in an Alpine ecosystem still rarely studied.

ECOSTRESS Reveals the Importance of Topography and Forest Structure for Evapotranspiration from a Tropical Forest Region of the Andes

“…Intermediate slopes can accommodate more trees per unit ground area than level areas, while past a certain threshold, slopes become too steep to support forest ecosystems [31,84], thus potentially influencing ET via changes in vegetation cover and tree density. In complex mountainous terrain, slope may additionally affect wind flow regimes and thus energy and water exchange [85]. It also affects soil water availability, which can constrain or enhance local ET; as such, previous studies reported enhanced (evapo)transpiration on slopes compared to waterlogged valley bottoms [77,83].…”

Comparison and applicability analysis of different evapotranspiration models for maize farmland in the lower Yellow River Plain based on the eddy covariance system

“…Relevant scholars have found that solar radiation is an important factor impacting the change in evapotranspiration. Related studies have emphasized that the net radiation, photosynthetically active radiation and vapor pressure deficit are important drivers of evapotranspiration (Wieser et al, 2008;Gisolo et al 2022;Shi et al 2022).…”