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

Abstract

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 ((Formula presented.), (Formula presented.), (Formula presented.), and (Formula presented.)) 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 (Formula presented.) = −0.19 month·100 mm−1 for “wetting” and (Formula presented.) = −0.13 month·K−1 for “warming”, while increasing gradients were found in the same regions with (Formula presented.) = +0.18 month·100 mm−1 for “wetting” and (Formula presented.) = +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.