Contribution of Biophysical Factors to Regional Variations of Evapotranspiration and Seasonal Cooling Effects in Paddy Rice in South Korea

Wei Xue,Jonghan Ko,Seungtaek Jeong,Jong-Min Yeom

doi:10.3390/rs13193992

Wei Xue, Jonghan Ko + Show 2 more

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https://doi.org/10.3390/rs13193992

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Abstract

Previous studies have observed seasonal cooling effects in paddy rice as compared to temperate forest through enhanced evapotranspiration (ET) in Northeast Asia, while rare studies have revealed biophysical factors responsible for spatial variations of ET and its cooling effects. In this study, we adopted a data fusion method that integrated MODIS 8-day surface reflectance products, gridded daily climate data of ground surface, and a remote sensing pixel-based Penman-Monteith ET model (i.e., the RS–PM model) to quantify ET patterns of paddy rice in South Korea from 2011 to 2014. Results indicated that the regional variations of the rice-growing season ET (RGS-ET, the sum of daily ET from the season onset of rapid canopy expansion (SoS) to the end of the rice-growing season (EGS)) were primarily influenced by phenological factors (i.e., the length of growing period-LGP), followed by growing season mean climatic factors (i.e., vapor pressure deficit-VPD, and air temperature). For regional variations of the paddy field ET (PF-ET, the sum of daily ET from the field flooding and transplanting date detected by satellite observations (FFTDsat) to SoS, and to EGS), the extents were substantially reduced, only accounting for 54% of the RGS-ET variations. The FFTDsat and SoS were considered critical for the reduced PF-ET variations. In comparison to the temperate forest, changes in monthly ground surface air temperature (Ts) in paddy fields showed the V-shaped seasonal pattern with significant cooling effects found in late spring and early summer, primarily due to a large decline in daytime Ts that exceeded the nighttime warming. Bringing FFTDsat towards late spring and early summer was identified as vital field management practices, causing significant declines in daytime Ts due to enhanced ET. Results highlighted climate-warming mitigation by paddy fields due to early flooding practices.

Highlights

The FAO’s annual proceedings have reported that around 167 million hectares of global land were plowed for paddy rice plantation in 2017, and more than 90% of global paddy rice areas were distributed in Northeast and Southeast Asia [1]
The SEM was applied to evaluate the magnitude and importance of the causal connection between the RF-ET and nine biophysical factors (Figure 3), including RGS-ET, biomass production, daily mean net radiation from the FFTDsat to the end of the rice-growing season (EGS), FFTDsat, daily mean and minimum air temperatures of the same period as the net radiation, season onset (SoS), LGP, the maximum leaf area index (LAI) of the rice-growing season, and daily mean vapor pressure deficit during the same period
We speculate that the significant effects of air temperature on spatial variations of RGS-ET were produced through their controls on dVPD

Summary

Introduction

The FAO’s annual proceedings have reported that around 167 million hectares of global land were plowed for paddy rice plantation in 2017, and more than 90% of global paddy rice areas were distributed in Northeast and Southeast Asia [1]. Rice is conventionally grown in fields that are flooded at different depths during the land preparation period (i.e., the first date of field flooding and transplanting detected by satellite observationsFFTDsat , referred to as the FFTDsat nominated surrogate of paddy rice land preparation, as commonly seen in the remote sensing research on regional paddy rice) until the end of the rice-growing season (EGS). Paddy rice with a water layer on the soil surface develops a wetland environment, which increases the water availability for evapotranspiration (ET). 2021, 13, 3992 of the absorbed shortwave energy during the daytime, leading to a non-radiative surface cooling effect [2,3]. A large number of reports focusing on the ET in paddy rice has indicated that the daily The positive effects of paddy fields on hydrological processes and ground surface climate changes through ET highlight the necessity for carrying out studies to disentangle important biophysical factors responsible for ET spatial variations and ET-related changes in the ground surface air temperature (Ts ).

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