Evaluating the Interplay Between Soil Moisture and Meteorological Drought Indicators: Implications for Drought Monitoring and Crop Productivity in India

Drought is a recurring and complex climatic event that can severely impact various sectors, including agriculture. Agricultural drought assessment typically focuses on the deficiency of soil moisture during the growing season, while meteorological drought pertains to below-average precipitation over several months to years. However, there has been limited comprehensive comparison of satellite-derived agricultural and meteorological drought indices to assess their effectiveness in monitoring drought across India's different climate regions and cropping seasons (Kharif and Rabi). Drought conditions often lead to a significant decrease in gross primary productivity (GPP). To understand the impact of drought on plant growth, we utilized GPP as an indicator. Our analysis focused on examining the relationship between various vegetation stress indicators, including SPEI-3 (Standardized Precipitation Evapotranspiration Index), Root Zone Soil Moisture (RZSM), and GPP. In most regions of India, RZSM outperformed SPEI-3 in identifying vegetation stress conditions. Additionally, we conducted a spatial correlation analysis between each stress indicator and GPP, aiming to monitor changes in these correlations over time, particularly in different climate zones. The goal of this analysis was to assess how well stress indices consistently describe crop conditions across different time points and regions in India. Pearson's correlation coefficients were calculated for each month spanning the years 2014 to 2018. These calculations encompassed all pixels, comparing pairs of GPP and the respective stress indices within specific climate zones. Results from the analysis provide valuable insights into how the strength of correlation varies over time, considering variations across different months and years and differences in climatic zones across India's crop-growing areas. Further, insights will be presented on how these stress indicators are performing across major growing seasons and their spatial variation.