Unravelling evapotranspiration controls and components in tropical Andean tussock grasslands

Abstract

The study of the environmental factors that control evapotranspiration and the components of evapotranspiration leads to a better understanding of the actual evapotranspiration (ET) process that links the functioning of the soil, water and atmosphere. It also improves local, regional and global ET modelling. Globally, few studies so far focussed on the controls and components of ET in alpine grasslands, especially in mountainous sites such as the tussock grasslands located in the páramo biome (above 3300 m a.s.l.). The páramo occupies 35 000 km 2 and provides water resources for many cities in the Andes. In this article, we unveiled the controls on ET and provided the first insights on the contribution of transpiration to ET. We found that the wet páramo is an energy-limited region and net radiation (Rn) is primarily controlling ET. ET was on average 1.7 mm/day. The monthly average evaporative fraction (ET/Rn) was 0.47 and it remained similar for wet and dry periods. The secondary controls on ET were wind speed, aerodynamic resistance and surface resistance that appeared more important for dry periods, where significantly higher ET rates were found (20% increase). During dry events, transpiration was on average 1.5 mm/day (range 0.7-2.7 mm/day), similar to other tussock grasslands in New Zealand (range 0.6-3.3 mm/day). Evidence showed interception contributes more to ET than transpiration. This study sets a precedent towards a better understanding of the evapotranspiration process and will ultimately lead to a better landatmosphere fluxes modelling in the tropics.

Water transport and tracer mixing in volcanic ash soils at a tropical hillslope: A wet layered sloping sponge

“…Transpiration of the tussock grass vegetation that covers the experimental hillslope only affects the rooted layer of the soil profile (up to 10–15 cm depth). However, this water flux represents only a small fraction of evapotranspiration in the study region (Ochoa‐Sánchez, Crespo, Carrillo‐Rojas, Marín, & Célleri, ). Evaporation and transpiration effects on the isotopic composition of soil water are likely suppressed by the local environmental conditions.…”

“…Evaporation and transpiration effects on the isotopic composition of soil water are likely suppressed by the local environmental conditions. That is, high relative humidity (annual average = 90%; Muñoz et al, ), low net radiation (annual average = 100 W m −2 ; Ochoa‐Sánchez et al, ), and sustained input of low intensity precipitation (Padrón et al, ) throughout the year. Thus, the soil water MTT estimations were unaffected by evaporation and transpiration effects.…”

Assessment of fog gauges and their effectiveness in quantifying fog in the Andean páramo

“…sock grasslands in the p aramo. According toOchoa-S anchez et al (2020), quantification of fog is needed to provide a better understanding of the Evapotranspiration process.Overall, this study furthers the advances of our understanding of the importance of fog to p aramo ecosystems and establishes the basement for coming studies on climate change and its effects on the hydrology, notably, the water yield from these ecosystems in the Andes. Further work is needed to quantify the contribution of fog to the water used by vegetation and to elucidate the ecohydrological role of fog.…”

A concerted research effort to advance the hydrological understanding of tropical páramos

“…However, when data are limited, errors can be as high as 30% (Carrillo‐Rojas, Silva, Córdova, Célleri, & Bendix, 2016; Córdova et al, 2015). Using an Eddy‐covariance tower, one of the highest in the world, evapotranspiration for páramos was measured, reporting values of around 620 mm yr −1 in southern Ecuador (Carrillo‐Rojas et al, 2019; Ochoa‐Sánchez, Crespo, Carrillo‐Rojas, Marín, & Célleri, 2020; Ochoa‐Sánchez, Crespo, Carrillo‐Rojas, Sucozhañay, & Célleri, 2019). At the same site, net radiation was reported as the primary control of ETa (Ochoa‐Sánchez et al, 2020); while meteorological observations highlighted the role of radiation and air humidity variation in the control of the hydrological system (Carrillo‐Rojas et al, 2019; Ochoa‐Sánchez et al, 2020).…”

“…Using an Eddy‐covariance tower, one of the highest in the world, evapotranspiration for páramos was measured, reporting values of around 620 mm yr −1 in southern Ecuador (Carrillo‐Rojas et al, 2019; Ochoa‐Sánchez, Crespo, Carrillo‐Rojas, Marín, & Célleri, 2020; Ochoa‐Sánchez, Crespo, Carrillo‐Rojas, Sucozhañay, & Célleri, 2019). At the same site, net radiation was reported as the primary control of ETa (Ochoa‐Sánchez et al, 2020); while meteorological observations highlighted the role of radiation and air humidity variation in the control of the hydrological system (Carrillo‐Rojas et al, 2019; Ochoa‐Sánchez et al, 2020). Furthermore, Buytaert and Beven (2011) emphasized the importance of non‐stationary hydrological processes such as changing evapotranspiration, infiltration, and routing due to vegetation growth.…”