基于耦合协调度的黄土高原地区NDVI与降水关系的变异诊断

植被是地表生态系统的重要"指示器",在能量交换、水循环、碳循环、生物地球化学循环和维持中发挥着重要作用,降水是影响植被变化的主要气候因子,研究两者之间的作用关系具有重要的意义和价值。利用Mann-Kendall趋势检验法和Hust指数分析了黄土高原地区归一化植被指数（NDVI）的变化趋势,使用相对发展率（RDR）指数和重心转移模型分析了NDVI变化的时空差异,并构建了基于耦合协调度理论和Pettitt检验方法的NDVI与降水关系的变异诊断方法,识别了黄土高原地区NDVI与降水关系的突变点,探讨了降水对NDVI变化的影响以及造成NDVI与降水关系变化的原因。结果表明：（1）黄土高原地区73.49%面积的NDVI在1998-2017年有呈现显著增加趋势（P<0.05）,大部分地区NDVI在未来依旧呈现增加趋势;（2）黄土高原地区丘陵沟壑区与高原沟壑区的NDVI增加幅度大于黄土高原地区整体的增加幅度,而北部风沙区和农灌区以及黄土高原地区边界区域的NDVI增加滞后于区域整体变化;（3） NDVI与降水耦合协调程度逐年增强,两者关系在2006年发生显著突变（P<0.05）;（4） NDVI呈现显著增加区域降水明显高于不显著变化区域（P<0.05）,降水对NDVI变化存在一定影响,在丘陵沟壑区、高原沟壑区北部和东部河谷及土石山区北部NDVI和降水存在显著正相关关系（P<0.05）,然而黄土高原地区大部分区域的降水并不存在显著变化趋势（P>0.05）,因此造成黄土高原地区NDVI与降水关系在2006年发生显著突变的主要原因应该是人类活动（P<0.05）。研究成果有助于进一步理解黄土高原植被变化与降水的相互作用,为黄土高原生态建设和水土流失治理提供一定的科学支撑。

Diagnosis of the relationship between NDVI and precipitation based on the coupling coordination degree

Vegetation is an important indicator of surface ecosystems, and plays an important role in energy exchange, water cycle, carbon cycle, biogeochemical cycle and maintenance. Among many environmental factors, precipitation is the main climatic factor that affects vegetation changes. Studying the relationship between Normalized Difference Vegetation Index (NDVI), which can reflect vegetation coverage, and precipitation has important meaning and value. In this study, the Mann-Kendall trend test and Hurst exponent were used to analyze the change trend of the NDVI in the Loess Plateau region. The relative development rate (RDR) exponent and the center of gravity shift model were used to analyze the spatial and temporal differences in NDVI changes in the Loess Plateau region. A change-point diagnosis method of the relationship between NDVI and precipitation based on the coupling coordination degree and Petttt test method were constructed, and the change-point of the relationship between NDVI and precipitation in the Loess Plateau area was identified. The impact of precipitation on the change of NDVI and the reason for the change in the relationship between NDVI and precipitation were discussed. The results showed that:(1) NDVI in 73.49% area of the Loess Plateau showed a significant increase from 1998 to 2017(P<0.05), and NDVI will continue to increase in most areas in the future. (2) The increase in NDVI in the hilly and gully areas of the Loess Plateau was greater than that of the overall increase in the Loess Plateau. However, the increase of NDVI in the northern sandstorm area, agricultural irrigation area, and the border area of the Loess Plateau lagged behind the overall regional change. (3) The coupling coordination degree between NDVI and precipitation was increasing year by year, and the coupling coordination degree between NDVI and precipitation had a change-point significantly in 2006(P<0.05). (4) Precipitation in significant increase areas of NDVI was higher than precipitation in non-significant increase areas of NDVI(P<0.05). Precipitation had a certain effect on NDVI changes. There was a significant positive correlation between NDVI and precipitation in hilly and gully areas, northern and eastern valleys of plateau gully areas, and northern soil and rocky mountainous areas(P<0.05). However, precipitation in most areas of the Loess Plateau did not had a significant change trend(P>0.05). The main reason for the significant change-point between NDVI and precipitation in 2006 should be human activities(P<0.05). Significant change-point in the overall NDVI of the Loess Plateau were 7 years behind the implementation of the policy of returning farmland to forests in the Loess Plateau(P<0.05), and vegetation restoration required a longer period of time. The results help to further understand the interaction of vegetation changes and precipitation on the Loess Plateau, and provide a certain scientific support for ecological construction and soil erosion control in the Loess Plateau.