Obtaining evapotranspiration and surface energy fluxes with remotely sensed data to improve agricultural water management

Abstract

4559 ABSTRACTThe quantification of evapotranspiration from irrigated areas is important for agriculture water management, especially in arid and semiarid regions where water deficiency is becoming a major constraint in economic welfare and sustainable development. Conventional methods that use point measurements to estimate evapotranspiration are representative only of local areas and cannot be extended to large areas because of heterogeneity of landscape. Remote sensing based energy balance models are presently most suited for estimating evapotranspiration at both field and regional scales. In this study, SEBAL (Surface Energy Balance Algorithm for Land), a remote sensing based evapotranspiration model, has been applied with Landsat ETM+ sensor for the estimation of actual evapotranspiration in the Habra plain, a semiarid region in west Algeria with heterogeneous surface conditions. This model followed an energy balance approach, where evapotranspiration is estimated as the residual when the net radiation, sensible heat flux and soil heat flux are known. It involves in the input the remote sensing land surface parameters such as surface temperature, NDVI and albedo. Different moisture indicators derived from the evapotranspiration were then calculated: evaporative fraction, Priestley-Taylor parameter and surface resistance to evaporation. These calculated indicators facilitate the quantitative diagnosis of moisture stress status in pixel basis. The study area contains extremes in surface albedo, vegetation cover and surface temperature. The land uses in this study area consists of irrigated agriculture, rain-fed agriculture and livestock grazing. The obtained results concern the validation of the used model for spatial distribution analysis of evapotranspiration and moisture indicators. The evaluation of daily evapotranspiration and moisture indicators are accurate enough for the spatial variations of evapotranspiration rather satisfactory than sophisticated models without having to introduce an important number of parameters in input with difficult accessibility in routine. In conclusion, the results suggest that SEBAL can be considered as an operational method to predict actual evapotranspiration from irrigated areas having limited amount of ground information.

Application of SEBAL and Ts/VI Trapezoid Models for Estimating Actual Evapotranspiration in the Algerian Semi-Arid Environment to Improve Agricultural Water Management

“…However SEBAL follows an energy balance approach, where the latent heat flux (corresponding to the energetic equivalent of ET) is estimated as the residual term when net radiation, sensible and soil heat fluxes are known, by using a rather complex hot and cold pixel based contextual approach to internally calibrate sensible heat flux through an iterative approach. SEBAL may not be as applicable as other models for ET spatialization over agricultural areas where ground information is scarce or difficult to collect (Khaldi et al, 2011). Moreover, SEBAL has the particularity of using a calibration procedure to compensate for temperature and albedo errors without the need for a complex atmospheric correction (Bastiaanssen et al, 2005).…”

Evapotranspiration and Surface Energy Fluxes Estimation Using the Landsat-7 Enhanced Thematic Mapper Plus Image over a Semiarid Agrosystem in the North-West of Algeria

“…Spatial resolution is 30´30 m on the optical bands and 60´60 m on the thermal band. This high spatial resolution is well suited for monitoring evapotranspiration on heterogonous landscapes (Khaldi et al, 2011).…”

“…However, the estimated latent heat flux should be considered with caution and have only a relative value, because there is no method of validation over wide scales of time and space (Khaldi et al, 2011).…”

“…It is recognized as the only way to retrieve evapotranspiration at several temporal and spatial scales (Zhang et al, 2016;Liou et al, 2014). To this end, there has been a major effort over the past several years to develop remote sensing-based methods that provide spatially distributed surface fluxes maps using airborne and satellite data (Khaldi et al, 2011). Basically, these methods can be classified into three main categories:…”

“…It constitutes the link between the hydrological and energetic equilibrium at the soil-vegetation-atmosphere interface and its knowledge is crucial for climatic and agrometeorological studies (Khaldi et al, 2011). Nearly two-thirds of precipitation over land is returned back to the atmosphere by the evapotranspiration (Jato et al, 2016).…”