Transition from rainfed to irrigated agriculture requires an accurate understanding of crop-water interactions. Conventional crop water stress indicators (CWSI) that quantify leaf water condition assumes a uniform distribution of temperature across the leaf (represented by the mean), which is rarely observed in rainfed conditions. This study is aimed at understanding the crop water status of rainfed cotton using three stress indicators (empirical: CWSIemp; statistical: CWSIstat; and simplified: CWSIsim). Performance of each index is evaluated by comparing with observed leaf water potential ( \(\:\psi\:\) leaf), and found to be low (R2emp = 0.66; R2stat = 0.54; R2sim = 0.51), thus recommending re-constitution. The stress indicators were then modified by considering spatial variability of temperature within the leaf as captured by a high-resolution thermal camera. Results showed that the modified index in statistical form (mCWSIstat) has outperformed other indices in estimating leaf water status (R2 = 0.82, r = 0.90) during the crop cycle. Dynamics of mCWSIstat are gradually increased from 0.20 ± 0.08 during flowering and reached the peak 0.80 ± 0.10 during boll bursting stage. The modified index is further used to ascertain the role of various environmental and biophysical factors. Among these factors, air temperature (R2 = 0.66, r = -0.81) and soil moisture (R2 = 0.62, r = -0.78) were found to be the key drivers of mCWSIstat. Our study revealed that crop water stress controls both carbon (R2 = 0.55, r = -0.74) and water (R2 = 0.72, r = -0.84) fluxes by regulating the stomatal conductance. The study findings can aid in the rapid assessment of crop water status from environmental conditions in rainfed crops, thus enabling effective management.
