China’s deserts greening and response to climate variability and human activities

RESEARCH ARTICLE China’s deserts greening and response to climate variability and human activities Xiaoyu LiuID1,2, Liangjie XinID1* 1 Key Laboratory of Land Surface Pattern and Simulation, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Science, Beijing, China, 2 College of Resources and Environment, University of Chinese Academy of Sciences, Beijing, China * xinlj@igsnrr.ac.cn Abstract Vegetation, which is a good indicator of the impacts of climate variability and human activi- ties, can reflect desert ecosystem dynamics. To reveal the vegetation variations in China’s deserts, trends in the monthly, seasonal, and annual normalized difference vegetation index (NDVI) from 2000 to 2017 were measured both temporally and spatially by the Theil-Sen estimator and Mann-Kendall test. Additionally, correlation coefficients and residual analysis were employed to evaluate the correlations between the NDVI and climatic factors and to distinguish the impacts of climate variability and human activities. The results showed that China’s deserts underwent greening. The annual NDVI showed a significant increasing trend at a rate of 0.0018/yr, with values of 0.094 in 2000 and 0.126 in 2017. Significant increasing trends in NDVI were observed in all four seasons. The NDVI were higher in sum- mer and autumn than in spring and winter. Both the monthly NDVI and its trends showed an inverted U-shaped curve during the year. Spatially, the greening trends were mainly distrib- uted on the southern edge of the Gurbantunggut Desert, in the northwestern part of the

Taklimakan Desert, and in the Kubuqi Desert. The correlations between the NDVI and cli- matic factors at the monthly and seasonal scales were stronger than those at the annual scale. Temperature and precipitation had positive effects on NDVI at the monthly and sea- sonal scales, but only precipitation had a positive effect at the annual scale. Human activi- ties, especially oasis expansion and sand stabilization measures, were two major causes of large increasing areas of desert greening in China indicated by the NDVI. Introduction Deserts are one of the major land-cover types, covering approximately one-third of the terres- trial area of the earth [1]. Due to topography, atmospheric circulation, latitude, ocean currents, etc., deserts, as a product of arid climatic conditions, are mostly located on the western coasts of continents near 30˚ north and south latitude [2,3]. There is still no universally accepted common or technical definition for deserts, only distinguished by characteristics (e.g., climate, weather, and hydrology) [4]. In addition, deserts are dynamic, and their boundaries are grad- ual and not clearly defined. In China, deserts are mainly distributed in the northwest, which is PLOS ONE PLOS ONE | https://doi.org/10.1371/journal.pone.0256462 August 30, 2021 1 / 20 a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 OPEN ACCESS Citation: Liu X, Xin L (2021) China’s deserts greening and response to climate variability and human activities. PLoS ONE 16(8): e0256462. https://doi.org/10.1371/journal.pone.0256462

Editor: Gerald Forkuor, United Nations University Institute for Natural Resources in Africa, GHANA Received: June 2, 2021 Accepted: August 6, 2021 Published: August 30, 2021 Copyright: © 2021 Liu, Xin. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: The temperature and precipitation data used in our manuscript were obtained through a request from the National Tibetan Plateau Data Center, which is not directly produced by us, but directly uses someone else’s data product. Due to data copyright issues, we are unable to upload the data directly. The data is currently open access and readers can access the data by requesting it directly on the platform (https://data.tpdc.ac.cn/en/). Temperature and precipitation data can be obtained at the following websites: temperature: https://data.tpdc.ac.cn/en/ data/71ab4677-b66c-4fd1-a004-b2a541c4d5bf/? q=1-km%20monthly%20mean%20temperature%