Frontiers in plant science · 2026
Responses of stable vegetation to drought accumulation timescales and time lags in the Weihe River Basin.
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Hu Xiangxiang, Shi Yaya
Аннотация
INTRODUCTION: This study aimed to distinguish drought accumulation timescale from response timing in stable vegetation in the Weihe River Basin.
METHODS: We analyzed MODIS enhanced vegetation index (EVI) and ERA5-Drought standardized precipitation evapotranspiration index (SPEI) data for 2003-2024 on the native 0.25° drought grid. Persistent land-cover classification required at least 18 valid annual classifications and a modal-class fraction of at least 80%. Four accumulation timescales (1, 3, 6, and 12 months) and 13 window-end lags (0-12 months) formed 52 response-exposure combinations. We controlled for growing-season month effects and a linear trend. We applied maximum-statistic tests with synchronized 2-year moving-block resampling and controlled the false discovery rate across cells using the Benjamini-Hochberg procedure.
RESULTS: The area-weighted mean of grid-cell partial correlations peaked at SPEI-12, lag 0 (r = 0.3216), with a mean slope of 0.00971 EVI units per SPEI unit. Of 190 eligible cells, 126 showed a corrected positive association, covering 69.68% of eligible stable-vegetation area. Grasslands and high-elevation areas had stronger descriptive responses. Relaxing valid-area coverage from 0.70 to 0.50 retained the basin-wide peak. Across detected cells, the median bootstrap reselection frequency of the observed best timescale-lag combination was 53.1%. Across 2,252 SPEI-3 grid-cell drought events, the mean EVI residual reached -0.00909 one month after onset (95% onset-year block-bootstrap interval, -0.01448 to -0.00439). Among 2,105 uncensored events, meteorological drought termination was confirmed a median of 3 months after the last dry month (interquartile range, 2-3 months).
DISCUSSION: The dominant association links vegetation condition to the 12-month water balance ending in the response month. These findings support monitoring that combines long-term water balance, early vegetation responses, and continued vegetation observations after meteorological drought termination.
METHODS: We analyzed MODIS enhanced vegetation index (EVI) and ERA5-Drought standardized precipitation evapotranspiration index (SPEI) data for 2003-2024 on the native 0.25° drought grid. Persistent land-cover classification required at least 18 valid annual classifications and a modal-class fraction of at least 80%. Four accumulation timescales (1, 3, 6, and 12 months) and 13 window-end lags (0-12 months) formed 52 response-exposure combinations. We controlled for growing-season month effects and a linear trend. We applied maximum-statistic tests with synchronized 2-year moving-block resampling and controlled the false discovery rate across cells using the Benjamini-Hochberg procedure.
RESULTS: The area-weighted mean of grid-cell partial correlations peaked at SPEI-12, lag 0 (r = 0.3216), with a mean slope of 0.00971 EVI units per SPEI unit. Of 190 eligible cells, 126 showed a corrected positive association, covering 69.68% of eligible stable-vegetation area. Grasslands and high-elevation areas had stronger descriptive responses. Relaxing valid-area coverage from 0.70 to 0.50 retained the basin-wide peak. Across detected cells, the median bootstrap reselection frequency of the observed best timescale-lag combination was 53.1%. Across 2,252 SPEI-3 grid-cell drought events, the mean EVI residual reached -0.00909 one month after onset (95% onset-year block-bootstrap interval, -0.01448 to -0.00439). Among 2,105 uncensored events, meteorological drought termination was confirmed a median of 3 months after the last dry month (interquartile range, 2-3 months).
DISCUSSION: The dominant association links vegetation condition to the 12-month water balance ending in the response month. These findings support monitoring that combines long-term water balance, early vegetation responses, and continued vegetation observations after meteorological drought termination.