Under the background of global warming, the severity, duration, and influencing scope of drought disasters in China are all increasing in recent years. Meteorological drought is a prerequisite for the occurrence of drought disasters. On the basis of clarifying the causes of meteorological droughts, it is of great scientific significance to improve the drought early warning ability, to propose drought disaster coping strategies and defense measures. This study comprehensively sorts out the research progress of the causes of meteorological drought in China. Firstly, in view of the regional differences in the drought formation causes in the various regions, the causes of drought are summarized respectively in Northwest China, North China, Northeast China, East China, South China, and Southwest China. Considering the time persistence of drought, based on the seasonal drought, two-season drought, and three-season drought, the main influencing factors on the formation of meteorological droughts with different durations in various regions are summarized respectively, from the aspects of cooling and warming flow transport, geopotential height field, and sea surface temperature field anomaly. Secondly, the scientific problems and future research directions on causes of meteorological drought are put forward. In previous studies, the analysis of drought causes mostly considered a single influencing factor, or considering the multiple influencing factors, but there is a lack of in-depth elaboration and research on the synergy between multiple factors. The contribution rate to drought formation and the quantitative relationship between these multiple influencing factors are urgent to study.
The temperature and precipitation in the Tibetan Plateau (hereinafter referred to as the ‘TP’) increase as a whole, and the vegetation of the plateau has changed significantly under the influence of climate change. This paper summarizes the research progress on plateau climate change and its impact on plateau vegetation coverage and normalized difference vegetation index (NDVI), phenology, net primary productivity (NPP), biomass carbon pool, plant diversity and so on, and the future directions of research are discussed and expected. The main conclusions are as follows: (1) In recent 60 years, the annual average temperature increased significantly with an average increase of 0.37 ℃ per 10 years, and the annual precipitation increased with an average increase of 10.40 mm per 10 years in the TP. The warm and dry trend of climate in the southeast of the TP and the warm and humid trend of climate in the northwest of the TP were obvious. (2) Under the background of overall improvement, the vegetation coverage and NDVI degraded in local regions of the TP. The improved area accounted for 67.7%-75.0% of the plateau total area, and they mainly distributed in the central and eastern regions. (3) Under of the influence of climate change, the green returning period of vegetation in the plateau advanced, the dry and yellow period postponed, and the growth period prolonged on the whole. However, there is a great debate on the green returning period of plateau vegetation in advance after 2000. (4) NPP of plateau vegetation increased significantly as a whole, while the increasing rate of NPP slowed down after 2000. NPP of vegetation increased significantly in southern Qilian Mountains and alpine meadows of northern Nianqing Tanggula Mountains, while it decreased in northern Tibetan Plateau, ‘one river, two rivers’ and the central and western regions of Tibet three river sources. (5) The biomass carbon pool of the plateau vegetation showed an increasing trend, which was carbon sink in general, and the spatial heterogeneity was obvious. The biomass carbon of alpine meadow and steppe increased significantly, while that of other grassland increased slightly, and even decreased in some areas. (6) The plant diversity in the plateau has changed significantly. Although the research results were different, there is no doubt that the climate change has affected significantly on species composition and plant diversity of alpine grassland community. It is suggested to strengthen data networking observation comparison and multi-scale effect research, deepen internal mechanism research and multi-factor comprehensive and quantitative analysis, strengthen sharing mechanism and improve the coping ability to climate change in the future, so as to promote ecological protection and high-quality development of the plateau.
The phenomenon of drought disaster chain caused by drought disaster and its secondary disasters has a great impact on natural environment, society, economy and so on. In order to review the current research of drought disaster chain, different definitions of drought disaster chain and its two development stages have been retrospected. Then the main contents of drought disaster chain has been summarized, including the classification of drought disaster chain, evolution mechanism and control measures. Moreover, the main research methods involved in the current research have also been reviewed, including qualitative analysis, correlation analysis, probability model based method, complex network based method, and so on. From the goal of building systematic disaster prevention and mitigation, the problems existing in the current research were finally identified. The top-level research design and quantitative results are still needed. In the future, with the support of multidisciplinary knowledge, we should establish the chain catastrophe theory and put forward a series of quantitative methods. The research of this paper will be helpful to systematically understand the current progress, key points and difficulties in drought disaster chain studies, and also provide some references for future research.
