The Impact of Cloud Cover on Crop Water Stress Index (CWSI) in a Semi-arid Region of Uttar Pradesh

In agricultural practices, the widely embraced plant-based index for irrigation scheduling is the Crop Water Stress Index (CWSI). However, the conventional estimation of CWSI often operates under the assumption of clear skies and abundant sunlight. This research endeavors to explore the applicability of CWSI across various sky conditions. In a semi-arid region of Uttar Pradesh, an experiment was conducted involving wheat crops subjected to five distinct irrigation treatments across five plots. Plots 1, 2, and 3 received 50% maximum allowable depletion (MAD) through drip irrigation, 25% MAD via drip irrigation, and 50% MAD through flood irrigation, respectively. Plot 4 was designated as a rain-fed plot, while plot 5 served as a replication of a farmer’s field. The study data underwent classification based on relative sunshine duration (n/N), offering insights into cloud cover. Lower baselines of the plant-stress index were derived from plot 2. Building upon this, an empirical CWSI was calculated for all plots. The research explored three distinct cases: a regular case encompassing all cloud conditions, and two additional cases (case 1 and case 2) representing specific cloud conditions with 1 > n/N > 0.7 and 0.5 < n/N < 0.7, respectively. Unique lower baselines were developed for each case, expressed as \(-1.29 \left(VPD\right)-2.91\) for the regular case, \(-1.47\left(VPD\right)-1.69\) for case 1, and \(-1.36\left(VPD\right)-1.06\) for case 2. Here, VPD (vapor pressure deficit), a function of air temperature and relative humidity, played a crucial role. Mean CWSI values varied across the cases: for the regular case, they were 0.09, 0, 0.33, 0.95, and 0.40 for plots 1, 2, 3, 4, and 5, respectively. In case 1, the mean CWSI for the same plots were 0.16, 0.02, 0.38, 0.92, and 0.52, and in case 2, they were −0.11, −0.05, 0.28, 0.97, and 0.23. The linear relationship between CWSI and soil moisture depletion yielded R2 values of 0.59 (regular case), 0.70 (case 1), and 0.55 (case 2), providing insights into the statistical significance of the findings.