The Modified SEBAL for Mapping Daily Spatial Evapotranspiration of South Korea Using Three Flux Towers and Terra MODIS Data

Yonggwan Lee,Seongjoon Kim

doi:10.3390/rs8120983

Abstract

Evapotranspiration (ET) is expected to increase by a considerable amount because of the impact of future temperature increase. Nowadays, the daily to seasonal ET maps can be used to provide information for a sustainable and adaptive watershed eco-environment. This study attempts to estimate the spatial ET of South Korea (99,900 km2), located within the latitudes of 33°06′N to 43°01′N and the longitudes of 124°04′E to 131°05′E, on a daily basis. The satellite-based image-processing model Surface Energy Balance Algorithms for Land (SEBAL) was adopted and modified to generate the spatial ET data. The SEBAL was calibrated using two years (2012–2013) of measured ETs by an eddy covariance (EC) flux tower at three locations (two in a mixed forest area and one in a rice paddy area). The primary inputs for the model were land surface temperature/emissivity (LST/E), the Normalized Distribution Vegetation Index (NDVI), albedo (Ab) from a Terra Moderate-resolution Imaging Spectroradiometer (MODIS) satellite, a digital elevation model, and wind speed and solar radiation (Rs) from 76 ground-based weather stations. When LST data were unavailable because of clouds and/or snow, the bias-corrected ground temperature measured at the weather stations was used. The NDVI and Ab were used as the monthly average value to maintain relatively stable values rather than using the original time interval data. The determination coefficient (R2) between SEBAL and the flux tower ET was 0.45–0.54 for the two mixed forest towers and 0.79 for the rice paddy tower reflecting the known characteristics of closed and open space ET estimation. The spatial distribution of SEBAL showed that the spatial ET reflected the geographical characteristics, revealing that the ET of lowland areas was higher than that of highland areas.

Highlights

Evapotranspiration (ET) is a term used to describe total loss of water from the Earth’s surface to the atmosphere by combined processes of evaporation from the open water bodies, bare soil and plant surfaces, etc. and transpiration from vegetation or any other moisture containing living surface [1], and a total loss from ET accounts for approximately 40% out of total amount of water resources in South Korea [2]
The Moderate-resolution Imaging Spectroradiometer (MODIS) LST exhibited a deviation of −16.14 K and an R2 of 0.79 compared with the ground measured LST (Figure 3b)
We find that Ra24 was unsuitable for South Korea and instead used Rs

Summary

Introduction

Evapotranspiration (ET) is a term used to describe total loss of water from the Earth’s surface to the atmosphere by combined processes of evaporation from the open water bodies, bare soil and plant surfaces, etc. and transpiration from vegetation or any other moisture containing living surface [1], and a total loss from ET accounts for approximately 40% out of total amount of water resources in South Korea [2]. The long-term trends shows the increasing direction in the northern part of Korea and decrease in the southwestern part of Korea [3], not changed in total amount during a hydrologic year. These changes hinder sustainable water resources management, because of the Remote Sens. Because ET has a large effect on other related hydrological processes, such as soil moisture dynamics, groundwater discharge, and runoff generation [5], the right understanding in ET variations can provide clues for solving water resources problems. The spatial distribution and temporal variation of ET is an important issue in the watershed hydrologic study [6]

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Conclusion