A New Crop Water Stress Index for Desert Agriculture Derived from Satellite Observations and Soil Hydraulic Parameters

Abstract:

The Southwestern U.S. and many other arid and semiarid regions of the world face serious water shortages that are projected to have momentous adverse impacts on irrigated agriculture. Consequently, optimizing water efficiency for crop production is becoming a critical issue for providing water and food security in a changing climate. However, optimizing irrigation at the field scale is challenging due to highly heterogeneous soil and moisture conditions, both of which strongly affect water availability in the root zone. To inform efficient irrigation management, satellite remote sensing techniques can be applied to map soil moisture and actual evapotranspiration (ETa) at the field scale to quantify time- and space-varying crop water stress. The commonly used index for detection of crop water stress is derived from remotely sensed infrared measurements of foliage temperature. Application of satellite observations for estimating crop water stress at the field scale has been hampered by the difficulty of measuring foliage temperature in partially vegetated fields, owing to the coarse resolution (pixel size >100 m) that captures a composite of both soil and plant temperatures. Another issue is the strong dependence of canopy temperature on ambient atmospheric parameters. In this study, we introduce a new remote sensing-based crop water stress index (CWSI) that combines surface reflectance measurements from the Sentinel-2A/B and VENµS satellites with soil water retention data to estimate near-real time crop water stress at high spatial resolution (5 m) as a function of soil matric potential and evapotranspiration rate. To test the capability of the new index to capture water stress signals, daily CWSI maps are compared with eddy covariance measurements and thermal infrared CWSI estimates, as well as with the ECOSTRESS evaporative stress index across variably cropped fields in Yuma, Arizona. The advantage of the new index for near-real time monitoring of crop stress and its potential application for precision irrigation management at the farm level are discussed.