Using very high resolution thermal infrared imagery for more accurate determination of the impact of land cover differences on evapotranspiration in an irrigated agricultural area

Authors: CHENG, J. - Beijing Normal University; Kustas, William - Bill

Submitted to: Remote Sensing
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/30/2019
Publication Date: 5/5/2019
Citation: Cheng, J., Kustas, W.P. 2019. Using very high resolution thermal infrared imagery for more accurate determination of the impact of land cover differences on evapotranspiration in an irrigated agricultural area. Remote Sensing. 11(6):613. https://doi.org/10.3390/rs11060613.
DOI: https://doi.org/10.3390/rs11060613

Interpretive Summary: Urbanization, often of previously agricultural areas, alters the land cover significantly affecting water use and evapotranspiration (ET). This study showed the utility of very high resolution (~ 8 m) ET mapping using airborne remote sensing and a land surface model in determining the impact of land cover on water use compared to satellite ET at 90 m resolution over a mixed agricultural-urban area in China. The very high resolution aircraft imagery can more accurately determine the change in the magnitude of ET by having pure pixels of the main land cover types, namely urban and agriculture, while at the coarser 90 m resolution, the ET estimates are more often a mixture of urban and agricultural ET, especially near the urban-agriculture land cover boundaries. This study demonstrates the utility of very high resolution ET mapping for more reliable information for water resource management of agricultural areas undergoing urban encroachment.

Technical Abstract: Land cover has a strong effect on the evapotranspiration (ET) and the hydrologic cycle. Urbanization alters the land cover affecting the surface energy balance and ET, such as urban encroachment in agricultural areas. This study investigates the potential utility of high resolution evapotranspiration (ET) in determining more accurately the impact of land cover on water use for an agricultural area. The approach was to apply the physically-based two-source energy balance (TSEB) model to very high resolution (~ 8 m) aircraft thermal data and compare the ET pattern and distribution to TSEB output using the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data acquired on August 2, 2012. Modeled flux components were validated using measurements collected from a network of 16 eddy-covariance (EC) towers at the study site. The modeled ET using the aircraft data agreed satisfactorily with the flux tower measurements and had better performance than the TSEB model applied to the ASTER data. The percent errors between ET closed by Bowen Ration (BR) and residual (RE) approaches were 3% and 1%, respectively. It is shown that the high resolution aircraft ET can more accurately determine the change in ET magnitude by having pure pixels of the main land cover types, namely urban, agriculture and natural vegetation. As a result, the ET histogram exhibits a significant bi-modal distribution which can be used to accurately distinguish the impact on ET from urban versus agricultural land cover areas and potentially monitor the effect on ET over a landscape due to small changes in land cover At the coarser 90 m resolution of ASTER, the TSEB ET estimates are more often a combination of urban and agricultural land cover ET near the urban-agriculture land cover boundaries. As a result, the bi-modal distribution in ET is almost nonexistent. This study demonstrates the potential utility of high resolution ET mapping for more accurately determining the magnitude of the ET differences between cropland and urban land cover. It also suggests that with high resolution thermal imagery, TSEB is a potential tool for monitoring the impact on ET due to relatively small changes in land cover as a result of urban expansion useful for watershed management.