Журнал дистанционного зондирования и ГИС

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Evaluation of the Ecosystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS) Evaporative Stress Index at Micro and Macro Climate Levels Using Field Measurements in the San Francisco Bay Area

Amanda Croteau, Marisol Zepeda, Christopher Potter

Ecosystems in northern California have experienced repeated and prolonged droughts over the past 20 years. To improve predictive capabilities for impending hot and dry periods, the ratio of Actual Evapotranspiration (AET) to Potential Evapotranspiration (PET) has been shown to be a useful index for monitoring the moisture of vegetation. The main objective of this study was to “ground truth” the Evaporative Stress Index (ESI) from NASA’s ECOSTRESS sensor across eight different county parks within the San Francisco Bay Area using field measurements of soil moisture and leaf stomatal conductance collected in the summer of 2020. To initially validate ECOSTRESS ESI image data, daily PET rates from stations in the California Irrigation Management Information System (CIMIS) were used for comparison at the meso-climate level of >10 km. Correlation results showed that ESI could accurately track CIMIS PET during both 2019 and 2020. At the micro-climate level of >1 km across the county parks, daily average ECOSTRESS ESI failed to closely track either stomatal conductance or soil moisture content at sampling locations where oak woodland cover was predominant. We hypothesized that this mismatch was due to oak trees’ ability to root deep within the soil, allowing it to access water from lower levels not accounted for by ESI surface observations. Sampling sites where oak trees were not the predominant woodland cover showed higher correlation results between ESI and stomatal conductance, however, ESI failed to closely track soil moisture content at the micro climate site level. When all of the study sites were separated between oak-dominated and non-oak-dominated and averaged by county park, there was a significant correlation between soil moisture content and daily average ESI. It was concluded that at sites dominated by a mixture of oak trees and other woodland plant species, ESI is unable to accurately track the differences in each species’ stomatal conductance rates measured during the dry summer season.