Modelling evaporation processes in soils from the Huasco salt flat basin, Chile

Water Resources Research

Meruane

2017

Altiplanic wetlands are unique ecosystems located in the elevated plateaus of Chile, Argentina, Peru, and Bolivia. These ecosystems are under threat due to changes in land use, groundwater extractions, and climate change that will modify the water balance through changes in precipitation and evaporation rates. Long‐term prediction of the fate of aquatic ecosystems imposes computational constraints that make finding a solution impossible in some cases. In this article, we present a spectral model for long‐term simulations of the thermodynamics of shallow wetlands in the limit case when the water depth tends to zero. This spectral model solves for water and sediment temperature, as well as heat, momentum, and mass exchanged with the atmosphere. The parameters of the model (water depth, thermal properties of the sediments, and surface albedo) and the atmospheric downscaling were calibrated using the MODIS product of the land surface temperature. Moreover, the performance of the daily evaporation rates predicted by the model was evaluated against daily pan evaporation data measured between 1964 and 2012. The spectral model was able to correctly represent both seasonal fluctuation and climatic trends observed in daily evaporation rates. It is concluded that the spectral model presented in this article is a suitable tool for assessing the global climate change effects on shallow wetlands whose thermodynamics is forced by heat exchanges with the atmosphere and modulated by the heat‐reservoir role of the sediments.

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Spectral model for long‐term computation of thermodynamics and potential evaporation in shallow wetlands

Water Resources Research

Meruane

2017

“…The hydrological functioning of the high Andean basins in the Altiplano region is characterized by semi-arid to hyper-arid climate and endorheic conditions [1]. In this area, water is crucial for natural habitats, industry, and agriculture.…”

Section: Introductionmentioning

confidence: 99%

E-DATA: A Comprehensive Field Campaign to Investigate Evaporation Enhanced by Advection in the Hyper-Arid Altiplano

Suárez

Lobos

et al. 2020

Water

Self Cite

In the endorheic basins of the Altiplano, water is crucial for sustaining unique ecological habitats. Here, the wetlands act as highly localized evaporative environments, and little is known about the processes that control evaporation. Understanding evaporation in the Altiplano is challenging because these environments are immersed in a complex topography surrounded by desert and are affected by atmospheric circulations at various spatial scales. Also, these environments may be subject to evaporation enhancement events as the result of dry air advection. To better characterize evaporation processes in the Altiplano, the novel Evaporation caused by Dry Air Transport over the Atacama Desert (E-DATA) field campaign was designed and tested at the Salar del Huasco, Chile. The E-DATA combines surface and airborne measurements to understand the evaporation dynamics over heterogeneous surfaces, with the main emphasis on the open water evaporation. The weather and research forecasting model was used for planning the instruments installation strategy to understand how large-scale air flow affects evaporation. Instrumentation deployed included: meteorological stations, eddy covariance systems, scintillometers, radiosondes and an unmanned aerial vehicle, and fiber-optic distributed temperature sensing. Additional water quality and CO2 fluxes measurements were carried out to identify the link between meteorological conditions and the biochemical dynamics of Salar del Huasco. Our first results show that, in the study site, evaporation is driven by processes occurring at multiple spatial and temporal scales and that, even in the case of available water and energy, evaporation is triggered by mechanical turbulence induced by wind.

“…Shokri and Or (2011) showed that the vertical diffusion of water vapor across ξ is the transport mechanism that mobilizes water vapor toward the atmosphere. Sophisticated models that consider vertical transport of water (liquid and gas phases) from the water table to the surface can be implemented for computing E (Hernández‐López et al, 2014, 2016; Sakai et al, 2009). However, these models require solving the water transport equations in the soil and coupling them to the atmospheric boundary layer (Davarzani et al, 2014), which makes them difficult to use in hydrological systems where surface water and ground water interact.…”

Section: Introductionmentioning

confidence: 99%

Evaporation From Unsaturated Soils as a Function of the Air and Soil Sides of the Land Surface

Amesti

Water Resources Research

Suárez

2020

Self Cite

A theoretical framework for computing the evaporation from unsaturated soils is presented and validated based on laboratory experiments that were conducted in an uncontrolled environment where forcing variables vary in time according to diurnal meteorological cycles. This theory introduces a dimensionless number that controls the ratio between the actual and potential evaporation from unsaturated soils. The dimensionless number depends on the transfer velocity, which characterizes evaporation into the atmosphere, the diffusion coefficient of water vapor in the soil, and the water table depth. We show that depending on the value of the dimensionless number, evaporation can be limited by either the air-side or the soil-side of the land surface. For large transfer velocity values, evaporation is controlled by water vapor diffusion in the soil, while for shallow water tables, evaporation is controlled by water vapor transport from the land surface into the atmosphere. Despite the good agreement between the shape of the observed and predicted evaporation rates, a fitted dimensionless parameter is required to match the predicted evaporation rates. Possible explanations for this disagreement are given in the discussion. Plain Language Summary This article seeks to understand and quantify the hydrological cycle in closed basins that are found in the Altiplano region of the Andes Cordillera of South America. These closed basins are found in the desert and, by definition, have no outflow rivers, so the water that precipitates in the catchment must be completely evaporated within the catchment. An important part of this evaporation occurs in the open wetlands (many of which are protected by both national and international laws), which are found in the central depression of the basin, as well as in from the surrounding desert, where groundwater is located at a certain depth below the land surface. In this article, we propose and validate a simple expression for computing soil water evaporation and conduct laboratory experiments in an uncontrolled environment where air and soil temperatures, air humidity, and wind speed vary over time according to diurnal meteorological cycles. where E denotes evaporation expressed as (kg H2O /m 2 /s), k t is the transfer velocity (m/s), ρ v∞ is the water vapor concentration (kg H2O /m 3) far away from the surface, and ρ vi is the water vapor concentration (kg H2O /m 3) at the surface. Note that kg H2O and kg air are used to differentiate between water vapor mass and air mass, respectively. Both ρ v∞ and ρ vi can be written as follows (Brutsaert, 1982; Stull, 1988