Postdoctoral Scholars Association

The growing water scarcity in California has heightened interest in investigating agricultural irrigation water conservation strategies. This study examines the diurnal crop water stress index (CWSI) using micrometeorological data from the Tree Crop Remote Evapotranspiration eXperiment (T-REX) over four almond orchards in California. Diurnal variation of air-canopy temperature difference (T_c−T_a) is used to estimate the upper and lower baseline of the theoretical CWSI. This theoretical framework relies on the surface energy balance equation. This approach assumes that the aerodynamic resistance (r_a) is driven by turbulent transport of heat, water vapor, and momentum and is modeled using the Monin-Obukhov Similarity theory, incorporating atmospheric heat and momentum transfer. As expected, we found an overall higher T_c than T_a over the entire year, and the temperature difference between the two ranges within ±10°C. The CWSI during the daytime lies in its usual range (0–1) with a mean of ~0.6 (moderately stressed), and we further noted a significant control of actual evapotranspiration (ET) on its temporal variability in addition to net ecosystem productivity. The preliminary study results opened pathways for investigating surface energy fluxes on almond stress dynamics at multi-temporal and -spatial scales.