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

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 km 2 ), 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 (R 2 ) 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.

COMS-Based Retrieval of Daily Actual Evapotranspiration over Korea

“…Several methods have been developed to estimate ET from remotesensing data including empirical and statistical methods with remotely sensed vegetation indices [16][17][18], physical models that calculate ET as the residual of SEB using remotely sensed thermal infrared (IR) data [19][20][21][22][23][24][25], and other physical models such as the Penman-Monteith equations [26], the revised Resistance-Surface energy balance and the PenmanMonteith (RS-PM) equations [27][28][29] and Priestley-Taylor equations [30][31][32]. On a global or continental scales, the spatial ET is provided by the European Organization for the Exploitation of Meteorological Satellites (EUMETSAT) Satellite Application Facility (SAF) on Land Surface Analysis (LSA) and the National Aeronautics and Space Administration (NASA).…”

Assessment of an Automated Calibration of the SEBAL Algorithm to Estimate Dry-Season Surface-Energy Partitioning in a Forest–Savanna Transition in Brazil

“…However, there is still a need to refine the endmembers selection process, which will further improve the model accuracy since estimations are sensitive to changes in endmembers [55][56][57][58]. Regional applications of the SEBAL are usually based on local meteorological measurements [52,55,59,60], including wind speed ( ), relative humidity ( ), and shortwave incident radiation ( ). On the other hand, large-scale estimations can potentially benefit from the use of global, gridded meteorological variables (e.g., reanalysis methods) due to their global spatial coverage and long time-series [17,21,24,[61][62][63].…”

Using SEBAL to Investigate How Variations in Climate Impact on Crop Evapotranspiration

“…The instantaneous value can be used to calculate the daily value because the evaporative fraction tends to be constant during daytime hours, although the H and λE fluxes vary considerably [19,24]. The difference between the instantaneous evaporative fraction at satellite overpass and the evaporative fraction derived from the 24-h integrated energy balance is marginal and may be neglected [19,25,26].…”