Abstract: This study explores the spatial distribution of flash drought characteristics from multi-source soil data, and quantifies the thresholds of soil moisture and vapor pressure deficit that lead to a decrease in solar-induced chlorophyll fluorescence under flash drought conditions, using a two-dimensional copula method. We also examines the thresholds’ spatial heterogeneity in different aridity zones and different vegetation types across China. The results show that in the period of 2001-2020, the northern region experienced flash droughts less than 8 times, lasting over 10 pentads, with intensities mostly at Levels 3-4. In contrast, the southern region experienced more than 8 times, lasting about 6-10 pentads, with intensities mostly at Levels 1-2. For soil moisture-dominated region, the soil moisture thresholds for SIF ≤ SIF40% are roughly 0.39 m3m-3, 0.35 m3m-3, 0.25 m3m-3, and 0.06 in the humid, sub-humid, semi-arid, and arid zones, respectively, and 0.38 m3m-3, 0.35 m3m-3, and 0.28 m3m-3 for forests, croplands, and grasslands, respectively. In vapor pressure deficit-dominated regions, the thresholds are around 7 hPa, 4 hPa, and 2.5 hPa in arid, humid and sub-humid, and semi-arid zones, respectively, and 5 hPa, 4 hPa, and 3 hPa for croplands, forests, and grasslands, respectively.

Key words: flash drought, soil moisture, vapor pressure deficit, Copula, vegetation, threshold