*3.2. Temporal and Spatial Variation of EVI in the Growing Season*

With the trend analytical method, the trend of EVI in the growing season of the study area for 16 years was drawn (Figure 5a). With the standard deviation classification method, the change trend of EVI in the study area can be divided into seven types, significant degradation, moderate degradation, slight degradation, basically unchanged, slight improvement, moderate improvement, and significant improvement (Figure 5b). On the whole, the EVI in the growing season in IMAR was basically unchanged, slightly improved, and slightly degraded. Among them, the basically unchanged areas were mainly in northern, central, and southeastern part of the study area, accounting for 42.5% of the area; and the vegetation types were mainly evergreen coniferous forests, deciduous coniferous forests, deciduous broadleaf forests, coniferous and broadleaf mixed forests, typical steppe and swamps. The areas with slight improvement were mainly in northeastern, west-central part of the study area, accounting for 21.1% of the total area; and the vegetation types were typical steppe and desert steppe. The areas where it displayed a slight degradation were mainly in the northern and southeastern part of IMAR, accounting for 24.6% of the total area; and the vegetation types were mainly typical steppe, desert steppe, deciduous coniferous forests and deciduous broadleaf forests. The areas with significant improvement mainly included Hinggan League, Hohhot, northern Xilingol League, western Hulunbuir, and southern Tongliao, accounting for 1.6% of the total area; and the vegetation types are shrubs, meadow steppe, deciduous broadleaf forests, and mixed coniferous and broadleaf forests. The areas with moderate improvement were mainly in Chifeng, northeastern Hulunbuir, central Xilingol, and southern Erdos, accounting for 5.9% of the total area; and the vegetation types included typical steppe, desert steppe, shrubs, and meadow grasslands. The areas with moderate degradation were mainly in Baotou, Ulanqab League, southwestern Xilingol League and eastern Hulunbuir, accounting for 3.5% of the total area; and the types of vegetation were swamps and typical steppe. The areas where there was a significant degradation were mainly located in central Hulunbuir, southeast of Xilingol League, and southeast of Ulanqab League, only accounting for 0.8%, a small part of the total area, and the vegetation types are shrubs and typical steppe. The vegetation types that showed a trend of improvement in the study area were mainly the typical steppe in the north-central part and the desert steppe in the southern part. The vegetation types that showed a trend of degradation were mainly desert steppe in the south and coniferous and broadleaf mixed forest in the north.

**Figure 5.** EVI trend (**a**) and EVI change (**b**) in the study area from 2000 to 2015.

## *3.3. Time Lag Analysis of EVI in the Growing Season to Climatic Factors*

Previous studies have shown that the response of vegetation index to climatic factors show significant differences in both time and space [49,50]. And different climatic factors have different impact on vegetation with certain degree of time lag effects [32,51,52]. The GRGs are computed using the EVI in the growing season (from May to September) with different climatic factors (mean air temperature, mean relative humidity, and accumulated precipitation) in different time series (from March to July, from April to August and from May to September), resulting in the largest GRGs between EVI and climatic factors being air temperature (from April to August), relative humidity, (from March to July), and precipitation (from April to August), with GRG mean values of 0.649, 0.609, and 0.623 respectively (Figure 6). It showed that the response of growing season EVI to air temperature and relative humidity lagged by 1–2 months, and the response of growing season EVI to precipitation lagged by one month. In other words, the vegetation in the growing season of the study area responded more quickly to precipitation, and more slowly to air temperature and relative humidity.

**Figure 6.** The GRGs of growing season EVI to air temperature, relative humidity and precipitation in February–June, March–July, April–August, and May–September.
