Evaluation of agricultural drought monitoring through the utilization of vegetation optical depth (VOD) and gross primary productivity (GPP)

Drought is one of the natural disasters that have a major impact on human survival, production and life, long-term meteorological drought causes water shortage of surface soil and vegetation, and eventually leads to agricultural drought. Therefore, agricultural drought monitoring research is of great significance for global agricultural production and food security. In this study, The VOD/GPP ratio was employed as an agricultural drought index to assess irrigated agriculture in Xinjiang. The correlation between VOD/GPP and SPEI as well as SSMI at various time scales in Xinjiang farmland was analyzed. By calculating the normal distribution probability of VOD/GPP, potential agricultural arid areas were identified, and the feasibility of VOD/GPP in characterizing agricultural drought was determined by comparing crop yields in those areas. The findings revealed the following: 1) The correlation between VOD/GPP and SPEI was higher in the northern slope of the Tianshan Mountains and southern Xinjiang, but low in most regions. Longer SPEI time scales showed lower correlations. 2) VOD/GPP exhibited a positive correlation with SSMI in northern Xinjiang, while most parts of southern Xinjiang showed a negative correlation. Correlation decreased with longer time scales. 3) The study identified Hami, Turpan, Hotan, and Kashgar as severely affected agricultural arid areas. Crop yields in Turpan were significantly lower than the Xinjiang average, corn yields in Hotan consistently fell below the Xinjiang average, and Yecheng, a county in Kashgar experienced a sharp decline in production since 2010. In conclusion, VOD/GPP can effectively serve as an indicator to characterize agricultural drought in Xinjiang, reflecting the impact of atmospheric and soil drought on crops and resulting in reduced crop yields.