B019-0006
Evapotranspiration trends in Spain: potential land surface-atmosphere feedbacks

Tuesday, 8 December 2020
Poster
Monica Garcia, Technical University of Denmark, Department of Environmental Engineering, Copenhagen, Denmark, Gorka Mendiguren González, DTU Environment, Environmental Engineering, Kgs Lyngby, Denmark, Sergio M Vicente-Serrano, Instituto Pirenaico de Ecología, Zaragoza, Spain, Maria Carmen Moyano, Universidad Politecnica de Madrid, Ingeniería Agroforestal,, Madrid, Spain, Alicia Palacios-Orueta, Universidad Politecnica de Madrid, Ingeniería Agroforestal, Madrid, Spain and Maria J. Santos, URPP Global Change and Biodiversity, University of Zurich, Geography, Zurich, Switzerland
Abstract:
Spain has shown two distinct trends in the past decades: an increase in primary productivity and a positive trend in the atmospheric evaporative demand. The vegetation needs to balance these increasing demands for evapotranspiration with the available water supply and optimize carbon assimilation by adjusting canopy conductance in the short term, and growth in the long term, which influences land surface-atmospheric feedbacks. However, the net effect of all these drivers on actual evapotranspiration (ET) and the capability of vegetation to keep up with a drying atmosphere is not clear in Spain at spatial resolutions of 1km.

Here we investigated annual and seasonal trends in ET for Spain based on the PT-JPL model at 1km between 2001-2017 and assessed whether these trends could be explained land use, greening and climate. In general, a divide between temperate and more humid ecosystems in the North and more arid ecosystems in the rest was found.

Our trend analysis revealed four hotspots of land-atmosphere interactions with different drivers along an aridity gradient:

(i) Dryland agriculture in an arid steppe emerge as a large hotspot of ET reduction related to decreases in water supply and radiative demand. Other hotspots included two opposite cases of LAI decreases/increases associated to decreases/increases in ET. The potential mechanisms suggested to explain the ET changes are based on water vapor trends implying an atmospheric feedback from LAI to water vapor: (ii) positive for decreasing LAIs (La Mancha vineyards) amplifying the decrease in ET and (iii) negative (counteracting the increase in ET due to high LAI) in the case of temperate, more humid forests in North stripe. Finally, (iv) in a temperate but warmer region (Southwest) the most outstanding driver was the increase in radiative demand. ET mostly increased in irrigated and forested areas while in the rest ET decreased suggesting tighter stomatal control in responses to drier atmospheric conditions.

These results suggest that even though ET might slightly increase, it is not enough to compensate the increases in evaporative demand, indicating that a very large part of Mediterranean ecosystems are under even stronger water stress due to land surface-atmosphere interactions.

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