*2.1. Study Area*

The study region covers the area from 50◦ N to 90◦ N and is characterized by long cold winters and short summers. There is very little precipitation and the temperature is low. As a result of the harsh environments, there are few vegetation types in the Arctic. As shown in Figure 1a, water occupies more than half of the area in the Arctic, and the dominant vegetation type are shrubland (dominated by woody perennials), savannas (tree cover 10–60%), and grasslands (dominated by herbaceous annuals (<2 m)). Savannas are distributed in relatively low latitudes, while most of the shrublands are located at high latitudes. Grasslands are mainly scattered west of Greenland. The average altitude of the Arctic is below 1000 m. Areas with higher elevations are mainly distributed in the northwestern region of Canada, the northeastern region of Russia, as well as the Greenland Island and surrounding areas.

**Figure 1.** (**a**) Location of the FLUXNET sites used in this study. The description of these sites is provided in Table 1. The base map is the land cover types of the Arctic. (**b**) The elevation distribution of the Arctic.


**Table 1.** Basic information regarding the FLUXNET sites of the Arctic.

WET: wetlands; ENF: evergreen needleleaf forests; GRA: grasslands; OSH: open shrublands; SNO: permanent snow and ice. N means the numbers of the data points of the sites after quality control.
