Marked observed interannual differences in the vegetation response to the trend towards a warmer and wetter climate in northwest China

Located in the interior of Eurasia and to the north of the Qinghai–Tibet Plateau, the Northwest China experiences severe drought conditions as moist air from the ocean is unable to travel the long distance and penetrate the region’s mountain barriers. These special geo-climatic conditions result in Northwest China being highly sensitive to climate change. In this study, the characteristics of the response of the normalized difference vegetation index (NDVI) to the trend towards a warmer and wetter climate in Northern China from 1982 to 2019 were investigated. The results show that there were significant differences between these trends for the periods 1982–2000 and 2000–2019, with overall precipitation decreasing before 2000 but increasing afterwards. After 2000, the rate of temperature increase also slowed down, whereas the NDVI increased at an obviously faster rate. Compared with the period 1982–2000, during the period 2000–2019, the NDVI was more affected by precipitation than by the temperature. The results of a normalized linear regression also show that, for most vegetation types, the temperature played a more dominant role during the period 1982–2000, whereas precipitation had a more significant effect on the NDVI during the period 2000–2019. However, it was also found that, throughout the study period, the precipitation had a greater impact on forest NDVI and the temperature had a greater impact on the NDVI in areas of bare land. In addition, the results show that the strength of the relationship between the NDVI and climate in northwest China changed over time, with the relationship between NDVI and precipitation tending to become stronger and the relationship between NDVI and temperature tending to become weaker. The results will provide a new understanding of the relationship between vegetation and climate in northwest China and help to better cope with the risks brought by climate change.