中巴经济走廊归一化植被指数(NDVI)时空变化及影响因素分析

The Impact of Climate and Land Use on the Spatio-temporal Changes of NDVI of China-Pakistan Economic Corridor

中巴经济走廊是“一带一路”重要组成部分,探究该地区归一化植被指数(NDVI)变化对当地生态环境改善具有重要意义。基于1995-2015年AVHRR GIMMS NDVI数据集,结合同期气候和土地利用类型数据,采用最大值合成法、Sen+MK趋势分析和偏相关分析法,分析中巴经济走廊植被NDVI时空变化趋势及其与气候、土地利用的关系。结果表明:(1)中巴经济走廊植被覆盖状况整体较差,近20年来植被NDVI整体上呈现波动上升趋势,但空间差异较明显,呈现由中部向南北递减的变化趋势;(2)中巴经济走廊地区植被NDVI以明显改善和基本稳定为主,其中,改善区域主要分布在巴基斯坦东北部和中国新疆喀什西部地区,基本稳定区域分布在巴基斯坦西南部和新疆东部地区;(3)中巴经济走廊地区年均温和年降水量在1995-2015年总体呈现波动上升趋势,与植被NDVI均呈现显著相关性,研究区气温抑制植被生长,而降水对植被生长起促进作用;各气候区中热带季风气候区植被NDVI最高,年增长速率最快;各气候区降水与植被NDVI均呈现正相关关系,而热带沙漠气候区植被NDVI与气温呈现负相关;(4)1995-2015年中巴经济走廊耕地、林地和草地平均NDVI呈现增加趋势,其中,耕地NDVI增长速率(0.002 4 a^(-1))最快,耕地NDVI增长对整个区域NDVI增加总量的贡献更大。研究结果可以为中巴经济走廊地区植被保护和区域生态环境改善提供科学依据和参考。

The China-Pakistan Economic Corridor is a flagship project of the Belt and Road Initiative, the change of the normalized differential vegetation index(NDVI) along the Corridor has a profound impact on the improvement of the local ecological environment. Based on the 1995-2015 AVHRR GIMMS NDVI data set, and in combination with data on the climate and land use types during the same period, the spatiotemporal shifts and trends of the vegetation NDVI of the Corridor, as well as the relationship between climate changes and land uses have been analyzed by using maximum value synthesis methods, the Sen+MK trend analysis and the partial correlation analysis. The results show that:(1) There is relatively poor vegetation coverage along the China-Pakistan Economic Corridor. Over the 20 years period, its overall vegetation NDVI had shown an upward trend, despite some fluctuations;however, the spatial difference is remarkable, showcasing a decreasing trend from the center to the north and south;(2) The vegetation NDVI along the Corridor has been generally improved and kept basically stable. The improved areas are mainly distributed in the northeastern part of Pakistan and the western part of Kashgar of Xinjiang, China, while the basically stable ones are located in the southwestern part of Pakistan and the eastern part of Xinjiang;(3) The average annual temperature and precipitation in the China-Pakistan Economic Corridor area demonstrated a fluctuating upward trend from 1995 to 2015, indicating a significant positive correlation with the changes in the vegetation NDVI. The temperature in the research area inhibits the growth of vegetation, whereas the precipitation promotes it. Among all the climate zones of the Corridor, the tropical monsoon climate delivers the highest vegetation NDVI, and with the fastest annual growth rate;precipitation and vegetation NDVI are positively correlated in all climate zones of the Corridor, but vegetation and temperature are negatively correlated in the tropical desert climate;(4) From 1995 to 2015, there was an increasing trend in the average NDVI of cultivated land, woodland and grassland in the Corridor. Specifically, the NDVI of cultivated land grew at the fastest speed(0.002 4 a^(-1)), contributing the most to the total increase in NDVI across the entire region. The results of this study can provide a scientific basis and reference for vegetation enhancement and regional ecological environment protection in the China-Pakistan Economic Corridor.