Characteristics of Spatial and Temporal Vegetation Index Variability and Its Responses to Temperature and Precipitation in Mongolia

The Mongolian Plateau, a vital ecological barrier in northern China, is of great importance for studying vegetation dynamics in Mongolia against the background of climate warming. Such studies can enhance our understanding of regional vegetation responses to global warming and contribute to the establishment of a stronger ecological barrier in northern China. Here, we analyzed the spatial and temporal characteristics of the NDVI (normalized difference vegetation index) in Mongolia using 8 km resolution GIMMS NDVI3g data from 1990 to 2022, along with temperature, precipitation, and elevation data. Trend analysis and correlation methods were used to examine the relationships between the NDVI and temperature, as well as precipitation. The results showed four important aspects of these relationships. (1) The NDVI in Mongolia increased significantly from 1990 to 2022 at a rate of 0.0015 yr–1 (P<0.05). (2) Mongolia's NDVI increased from 1990 to 2022 in 60.73% of the country. Of this total, the area with a significant increase accounted for 31.67% and was concentrated on the eastern and western edges. The area experiencing a significant decrease accounted for 15.67% and was mainly located on the southwestern edges. (3) The NDVI analysis revealed significant increasing trends in all regions except for those at elevations of 1500–2000 m. The greatest rate of increase was observed between 500 and 1000 m, and the increasing trend weakened as elevation continued to increase before gradually becoming significant again. Additionally, the NDVI increased significantly across different slopes, and the rate of increase decreased as the slope increased. (4) From 1990 to 2022, Mongolia's NDVI was mostly negatively correlated with temperature. This occurred over 66.75% of the total land area, with 17.21% of the region exhibiting a significant negative correlation, mainly in the southwest. Conversely, the NDVI demonstrated a positive correlation with precipitation, encompassing 86.71% of the total land area. Approximately 40.44% of the region had a significant positive correlation, primarily in the southwest. In conclusion, throughout the experimental period, the vegetation state in Mongolia improved. However, due to the warming and drying climate, more attention should be paid to vegetation degradation in the south-central region.