Progress and prospect on climate warming and humidification in Northwest China

The northwest region of China is located in the hinterland of Eurasia, far from the ocean. The significant topography of the Qinghai-Tibet Plateau makes it one of the most arid and semi-arid regions of the world. Consequently, it occupies a crucial position in the global climate and environmental system. The regional climate change is unique, the formation mechanism is complex, and the impact on society and natural environment is prominent. Especially, since the beginning of this century, the scientific understanding of climate transition from warm and dry to warm and wet in Northwest China has been put forward, which has aroused widespread concern in academia and even the community on the issue of climate change in Northwest China. A wide range of studies on the climate change trend, drive mechanism and influence characteristics in Northwest China have emerged, and a large number of research progress has been accumulated in the past thirty years. However, due to the different types, the length of the sequence and the spatial and temporal resolution of data used in previous studies, the different periods and regions of concern, and the different perspectives and dimensions, there have been some disagreements and even contradictory conclusions on climate change in the northwest region, resulting in some social and media debates. Some media even believe that Northwest China may become "Jiangnan" or return to "Han and Tang", and so on. In view of this, this paper systematically sorts out the historical climate change research in Northwest China, summarizes the existing research results, and comprehensively considers different perspectives and dimensions, and divides six stages of understanding the characteristics of warming and dry-wet change in Northwest China. On the millennium scale, the climate in Northwest China experienced two cold-dry periods and two warm-wet periods. From the 1950s to the middle of the 1980s, it showed significant warming and drying. In the middle of 1980s, warm and humid signal appeared in the west of Northwest China. From the long-term trend of half a century, the precipitation in the east and west of Northwest China showed a seesaw change under the background of climate warming. Since the early 1990s, the climatic warming and humidification process in the arid area of Northwest China has intensified. Since the beginning of this century, the warming and humidification in Northwest China has been increasing eastward and enhancement. Meanwhile, this paper summarizes the influencing mechanism of warming and wetting in Northwest China from two aspects of human activities and atmospheric circulation, evaluates the effects of warming and wetting on ecology, agriculture and water resources, and analyzes the future trend of warming and wetting and its possible risk. Finally, in view of the deficiencies and problems existing in the current research of warming and wetting in Northwest China, it is proposed that future research needs to make breakthroughs in key scientific issues such as the synergistic driving mechanism of atmospheric circulation, hydrology and ecology on warming and wetting, the change characteristics of extreme weather and climate events under the background of warming and wetting, the response characteristics of surface water circulation to warming and wetting, the internal relationship between warming and wetting and hydrology and ecology, the possible opportunity and risks of warming and wetting to water security, ecological security and food security, and the future climate trends and adaptation in Northwest China under the "double carbon" target.