Spatiotemporal Changes of Vegetation in the Northern Foothills of Qinling Mountains Based on Kndvi Considering Climate Time-Lag Effects and Human Activities

Abstract

Vegetation is fundamental to regulating the climate system and ensuring carbon balance. Recognizing the effects of climate change (CC) and human activities (HA) is vital for understanding shifts in vegetation. However, climate time-lag effects are rarely measured, resulting in an inadequate assessment of CC's effects on vegetation dynamics. In this study, firstly, based on the Landsat image dataset, the spatiotemporal variations of the kernel Normalized Difference Vegetation Index (kNDVI) in the northern foothills of the Qinling Mountains (NQLM) from 1986 to 2022 were analyzed. Then, the multiple regression residuals method, accounting for time-lag effects, was employed to determine the effects of CC and HA on kNDVI change. Finally, six patterns of kNDVI change were obtained based on the kNDVI trend and the changes of CC and HA to kNDVI. Our research found: (1) During the past 37 years, the kNDVI increased at a rate of 0.0061/a, the annual kNDVI increased in 84.82% areas of the NQLM, and the kNDVI decreased in 0.86% areas. (2) The kNDVI exhibited a positive correlation with both precipitation and temperature, kNDVI response to precipitation with 1-month time lag and 0-month for temperature. (3) The contribution of CC to kNDVI change was 84%, temperature and precipitation drive kNDVI change rates with 0.0012/a and 0.0039/a, respectively. The contribution of HA to kNDVI change was only 16%. (4) Among the six patterns of kNDVI change, CC and HA collectively contributed to kNDVI change, and the effect of CC alone was more significant than that of HA. These findings will assist the critical need for informed, sustainable vegetation restoration strategies in the NQLM.

Keywords: kNDVI, Climate Change, human activities, Time lag, Wavelet analysis