Validation of ETWatch using field measurements at diverse landscapes: A case study in Hai Basin of China

The latent heat of evapotranspiration (ET) plays an important role for water resource management in water scarcity areas. Compared to the water balance method or to in situ measurements, an operational integrated monitoring method of regional surface ET from remote sensing data is a potentially useful approach to achieve water saving. This study presents new algorithms for the aerodynamic roughness length for complex landscape, for gap filling for cloud days, and for data fusion at different resolutions, based on the Penman-Monteith equation. It also presents an improved algorithm for ET calculation with remotely sensed data for clear days. Algorithms were integrated into the ETWatch. The research objective was to present the enhanced features of the ETWatch algorithm and its validation in the 320,000 km(2) Hai Basin in Northern China. This area faces serious over-exploitation of groundwater. ET was modeled and extensive field campaigns were done to collect data on soil moisture depletion, lysimeter measurements, eddy covariance measurements, and water balance calculations at diverse landscapes. The overall deviation for individual fields on a seasonal basis was 12% and decreased to 6% for an annual cycle. For larger areas, the deviation was 3% for an annual cycle. These levels of deviation are within the error bands for in situ measurements. The study concludes that data sets from ETWatch are able to aid consumptive water use reduction management in the study area. (C) 2012 Elsevier B.V. All rights reserved.