Abstract
Abstract. The Chinese Loess Plateau is located in the north of China and has a significant impact on the climate and ecosystem evolvement over the East Asian continent. Estimates of evapotranspiration (ET) at a regional scale are in crucial need for climate studies, weather forecasts, hydrological surveys, ecological monitoring and water resource management. In this research, the ET of the Chinese Loess Plateau was estimated by using an energy balance approach and data collected during the LOess Plateau land-atmosphere interaction pilot EXperiments 2005 (LOPEX05). With the combined data of the Medium Resolution Imaging Spectrometer (MERIS), the Advanced Along-Track Scanning Radiometer (AATSR) and some other variables such as air temperature, crop height and wind speed, the instantaneous net radiation, sensible heat flux and soil heat flux were calculated; the instantaneous latent heat flux was derived as the residual term of energy balance, and then converted to daily ET value by sunshine duration. The calculated daily ET from the model showed a good match with the measurements of the eddy covariance systems deployed in LOPEX05. The minimum relative error of this approach is 9.0%, the cause of the bias was also explored and discussed.
Highlights
Evaporation is the process of water changing from a liquid state into a gas or vapor state, transpiration is the evaporation of water from a plant’s leaves, stem, flowers or roots back into the atmosphere
Many algorithms using remote sensing information to estimate ET have been developed, and from simple and empirical approaches to complex and data consuming ones. These can be put into two groups broadly: (1) to estimate ET by set empirical relation between ET and parameters that could be measured from meteorological satellites (Index, 1994; Boegh, 2002; McCabe et al, 2005); (2) to calculate the sensible heat flux first and obtain the latent heat flux as the residual of the energy balance equation, SEBAL (Bastiaanssen et al, 1998), SEBS (Su et al, 1999; Su, 2002), NTDI (McVicar and Jupp, 1999)
The land surface albedo was derived from SMAC and Medium Resolution Imaging Spectrometer (MERIS) data, it was portioned by the vegetation fractional coverage and the typical discrepancy between soil and canopy surface albedo, these were αv = αs − (1 − fv)δα αg = αs + fvδα where αs was the surface albedo of a mixed pixel derived from satellite remote sensing data; αg was the albedo above the bare soil surface; αv was the albedo above the canopy surface; δα was the typical discrepancy between the soil and canopy surface albedo (0.1 was taken in this research)
Summary
Evaporation is the process of water changing from a liquid state into a gas or vapor state, transpiration is the evaporation of water from a plant’s leaves, stem, flowers or roots back into the atmosphere. Many algorithms using remote sensing information to estimate ET have been developed, and from simple and empirical approaches to complex and data consuming ones These can be put into two groups broadly: (1) to estimate ET by set empirical relation between ET and parameters (vegetation index, temperature, albedo) that could be measured from meteorological satellites (Index, 1994; Boegh, 2002; McCabe et al, 2005); (2) to calculate the sensible heat flux first and obtain the latent heat flux as the residual of the energy balance equation, SEBAL (Bastiaanssen et al, 1998), SEBS (Su et al, 1999; Su, 2002), NTDI (McVicar and Jupp, 1999).
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