Assessing crop water stress during late kharif season using Normalized Diurnal Difference Vegetation Water Content (nddVWC) of Advanced Microwave Scanning Radiometer–Earth Observing System (AMSR-E)

AMSR-E derived vegetation water content (VWC) at predawn (01:30 LST) and afternoon (13:30 LST) were found to have differences relating to rainfall patterns (wet spell/dry spell) over the rainfed region during late kharif season (August–October). A new index called Normalized Diurnal Difference Vegetation Water Content (nddVWC), i.e., diurnal difference of VWC per unit leaf area index (LAI) was conceptualized to assess the spatiotemporal variations of crop water stress. The nddVWC was found to be significantly (p = 0.05) correlated with rainfall particularly at 3 days time lag. It is also found to have significant correlation with Drought Severity Index (DSI). Irrigated rice crop was used as a benchmark to characterize nddVWC to represent different intensity of crop water stress (no stress ≤0.4, moderate stress >0.4 to ≤0.8, high stress >0.8). Inter-year comparative analysis of temporal variations of nddVWC was performed to assess its sensitivity in characterizing the normal and sub-normal years in term of the intensity and the persistence of crop water stress. Persistent high/moderate stress condition was observed over Vidarbha meteorological subdivision during 2009 (drought year), whereas no stress condition was prevailing during 2005 (normal year), and the year 2008 showed an intermediate condition. The spatiotemporal patterns of nddVWC could capture the progression of crop water stress condition at regional level. The proposed index has potential to monitor crop water stress in the areas otherwise considered to be too densely vegetated for conventional soil moisture retrieval.