Based on GRACE (Gravity Recovery and Climate Experiment) satellite products, the TWS changes were calculated in drylands of northern China during the past two decades. And on this basis, the characteristics and causes of TWS changes were explored by using multi-source observations and model simulations. The results show that TWS in drylands of northern China decreased with a rate of 17.80±1.72 Gt per year during 2002-2020, which was also accompanied by various degrees of reduction in groundwater, root zone soil moisture and surface soil moisture. In drylands of northern China, the effects, such as climate warming and human water consumption, caused a substantial increase of evapotranspiration. The negative contributions of evapotranspiration overpassed the concurrently positive contributions of precipitation, and thus led to the decrease in TWS and increase in regional water stress.

In recent years, the urban ozone (O3) pollution in China has become increasingly serious. The characteristics of ozone pollution and its source analysis and prevention work have attracted the attention of experts and scholars. This paper reviewed the research on the temporal and spatial characteristics and influencing factors of ozone pollution in China. From the perspective of O3 pollution of China, high pollution areas appeared in eastern and northern China, and O3 pollution was concentrated in typical urban agglomerations. Pollution incidents were mainly concentrated in summer and autumn, and less pollution in winter. The average concentration of ozone in most areas increased year by year, and anthropogenic emissions of volatile organic compounds (VOCs) and nitrogen oxides (NOx) were important reasons for ozone pollution, and in different regions it had different sensitivity to each other; high temperature, low humidity, low wind speed conditions were conducive to the maintenance and development of ozone pollution, global warming affected local tropospheric ozone concentration, and tropospheric ozone pollution also affected climate change.

Under global warming, the mean warming trend over land surface was much faster than that over ocean surface, therefore, there was difference of warming between land and ocean. As the increase of global mean surface air temperature, the difference between land and ocean warming also gradually increased, but the warming ratio between land and ocean was nearly constant, and it was the maximum in mid-high latitude of the Northern Hemisphere. The current situation of researches on land-ocean warming contrast under global warming was summarized and reviewed in this paper. The transient and equilibrium responses of climate system to external forcing such as greenhouse gases were investigated to explore the mechanism of land-ocean warming contrast. The results show that the difference of heat capacity between land and ocean was not main reason, while the atmospheric humidity and lapse rate feedback was main reason of land-ocean warming contrast, and SST forcing and change of vegetation evapotranspiration, surface evaporation, cloud amount, precipitation and relative humidity all contributed to the land-ocean warming contrast in short time scale. The simulated land-ocean warming ratio was basically consistent with the observations. However, it was excessively underestimated in mid-high latitude of the Northern Hemisphere, which might be related to the feedback of albedo induced by evergreen broad-leave forest expansion and between blocking and land-sea thermal contrast.