Impact of land use/land cover types on surface humidity in northern China in the early 21st century

In the context of global change, it is essential to promote the rational development and utilization of land resources, improve the quality of regional ecological environment, and promote the harmonious development of human and nature for the regional sustainability. We identified land use/land cover types in northern China from 2001 to 2018 with ENVI images and ArcGIS software. Meteorological data were selected from 292 stations in northern China, the potential evapotranspiration was calculated with the Penman—Monteith formula, and reanalysis humidity and observed humidity data were obtained. The reanalysis minus observation (RMO, i.e., the difference between reanalysis humidity and observed humidity) can effectively characterize the impact of different land use/land cover types (forestland, grassland, cultivated land, construction land, water body and unused land) on surface humidity in northern China in the early 21 st century. The results showed that from 2001 to 2018, the area of forestland expanded (increasing by approximately 1.80×10 4 km 2 ), while that of unused land reduced (decreasing by approximately 5.15×10 4 km 2 ), and the regional ecological environment was improved. Consequently, land surface in most areas of northern China tended to be wetter. The contributions of land use/land cover types to surface humidity changes were related to the quality of the regional ecological environment. The contributions of the six land use/land cover types to surface humidity were the highest in northeastern region of northern China, with a better ecological environment, and the lowest in northwestern region, with a fragile ecological environment. Surface humidity was closely related to the variation in regional vegetation coverage; when the regional vegetation coverage with positive (negative) contributions expanded (reduced), the land surface became wetter. The positive contributions of forestland and water body to surface humidity were the greatest. Unused land and construction land were associated with the most serious negative contributions to surface humidity. Affected by the regional distribution pattern of vegetation, surface humidity in different seasons decreased from east to west in northern China. The seasonal variation in surface humidity was closely related to the growth of vegetation: surface humidity was the highest in summer, followed by autumn and spring, and the lowest in winter. According to the results, surface humidity is expected to i