| Evapotranspiration plays a crucial role in the surface hydrothermal balance.On a regional scale,an accurate estimate of evapotranspiration in blown-sand regions,in particular,has important guiding significance for a rational allocation of water resources and drought monitoring.In this study,we chose the blown-sand region in the Ordos Basin as our research area.Based on six sets of Landsat8 remote sensing imaging data obtained in 2015-2016 and the corresponding surface meteorological observational data,we estimated the surface evapotranspiration in this area by adopting the Surface Energy Balance Algorithm for Land?SEBAL?model built on the basis of the principle of equilibrium.We then tested the accuracy of our result by introducing the FAO Penman-Monteith equation to calculate the evapotranspiration of the reference crop,based on which we also analyzed the characteristics of temporal and spatial distributions of evapotranspiration in the research area.Our results show that:1)The estimates for key surface parameters in this study show that?1?the mean surface albedo varies spatially between 0.16 and 0.245;?2?the surface albedo is smaller in vegetation-covered regions than in barred sand dunes,and high surface albedo values appear in saline fields on the southeast side of Baozhainur Lake;?3?the surface emissivity does not show much variation with time in the research area but is significantly affected spatially by the underlying surface,leading to a distribution pattern with the highest emissivity values in the central lake region and the lowest values in barred sand dunes;and?4?the surface temperature is significantly affected by seasons and the properties of the underlying surface,so the surface temperature is the lowest in the lake region in winter when water freezes,while the surface temperature is the highest in the sand dunes in summer;the difference between the maximum and minimum temperatures can reach up to 39 K.2)the daily evapotranspiration in the research area shows seasonal variability:June(4.85mm·day-1)>August(3.21 mm·day-1)>April(2.17 mm·day-1)>October(1.65mm·day-1)>February(0.74 mm·day-1)>December(0.40 2.17 mm·day-1),which highest in summer,lower in fall and spring,and lowest in winter;3)the evapotranspiration in the research area is distinctly characterized by its spatial variability,which is related to the terrain and geomorphology in this area as well as the effect of human activities;specifically,the regional evapotranspiration is higher overall in the east and lower in the west and distributed as alternating stripes along the NW-SE direction,which is generally consistent with the terrain,geomorphology,and distribution characteristics of sand dunes in this area;4)the daily evapotranspiration in the research area estimated by the SEBAL model was also tested using the FAO Penman-Monteith model,which yielded an average error of 19.5%,demonstrating that the SEBAL model can be applied to robustly estimate the evapotranspiration in the blown-sand region in the Ordos Basin.In summary,the remote-sensing-data-based SEBAL model can be applied to robustly estimate evapotranspiration in blown-sand regions,and the result from this study provides an important reference for future studies of water circulation,rational utilization of water resources,and protection of the ecological environment in this region. |
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