Assessing crop water deficit using MODIS data during winter wheat growing period along the lower reaches of the Yellow River, China

The Weishan Irrigation Zone along the lower reaches of the Yellow River consists of a total irrigated area of 3600 ha. The region has an average annual rainfall of 500–600 mm, with 60–70% of local rainfall occurring during the summer, and with less than 15% in spring. The water deficit during the spring affects the winter wheat growth from March to early June, which is a major growth period significantly impacting overall wheat production. Remote sensing has been an efficient guide for irrigation agriculture by providing regional estimates of crop water deficits. Daily Terra and Aqua MODIS surface reflectance and temperature products from March to June 2006 were collected and the Surface Energy Balance System (SEBS) was applied to model the turbulent energy flux. A drought severity index (DSI) derived in SEBS and the normalized difference water index (NDWI) were used to evaluate the canopy water deficit during the growing period. Combing with in situ soil moisture and crop growth observations, it was found that DSI can provide reasonable estimates of crop water deficits. NDWI can be used as an index for vegetation water content (VWC) but can not be used for crop water stress detection without knowing the ideal status of crop growth.