Asymmetrical Time-Lagged Response of Vegetation to Drought and Extreme Precipitation Across China

In this study, a study area was chosen in China to analyze the lagged response relationship between normalized difference vegetation index (NDVI) and extreme precipitation/drought from 1982 to 2015. A logistical function was applied to explain the increase in NDVI with mean annual precipitation in nine sub-regions, and the inflection point of precipitation was found to be very close to the threshold value for separating arid or humid regions. NDVI had a strong positive correlation with drought and extreme precipitation in the arid regions, while in humid regions, it presented a strong correlation with drought during 2000–2015; however, a weak correlation with drought was found before the 21st century. In this study, we quantified the time-lagged response of vegetation to drought (LTRD) and extreme precipitation (LTREP). Then, we defined four gradients (∂LTRD∂P, ∂LTRD∂T, ∂LTREP∂P, and ∂LTREP∂T) to quantify the precipitation and temperature gradients with the lag-time response to drought or extreme precipitation, respectively. Decreasing gradients were observed for humid regions with ∂LTRD∂P = −0.19 month·100 mm−1 for “wetting” and ∂LTRD∂T = −0.13 month·K−1 for “warming”, while increasing gradients were found in the same regions with ∂LTREP∂P = +0.18 month·100 mm−1 for “wetting” and ∂LTREP∂T = +0.14 month·K−1 for “warming”. These results suggest that the lagging responses of vegetation to extreme precipitation and droughts exhibit opposing regional patterns across China.