From the afternoon to night on 5 July 2021, severe convective weather including short-time heavy precipitation, thunderstorm wind and small hail occurred in the central region of Beijing-Tianjin-Hebei. The atmospheric environmental conditions and mesoscale characteristics of the formation of this weather process were analyzed by using the data of egional automatic meteorological station, Doppler radar, FY-2G meteorological satellite and microwave radiometer, and the fifth generation atmospheric reanalysis ERA5 from European Centre for Medium-Range Weather Forecasts. The results show that favourable water vapor conditions appeared before the occurrence of the severe convective weather including heavy precipitation, thunderstorm winds and local hail. Strong convergence of water vapor fluxes in lower and middle layers occurred 1 to 2 hours earlier than precipitation. The whole layer atmospheric precipitable water had accumulated continuously under strong uplift. The heat and power unstable environment of severe convection breaking out was created by formation of vertical θ_se energy frontal zone, maintenance of "upper dry and lower wet" unstable stratification, establishment of strong vertical wind shear from 0 to 6 km and enhancement of CAPE, K and SI indexes. Unstable stratification formed by eastward movement of the upper though carrying dry and cold air southward and low warm tongue, which had provided synoptic-scale upward movement for the occurrence of severe convection. The strong convective happening released more energy in the afternoon than in the evening. Heavy rainfall caused the local temperature to drop significantly and cold pool effect was more significant, which corresponded to the heavy precipitation area during the southward movement process. The surface convergence line at the cold pool boundary was the mesoscale trigger system. The cloud base height dropped and infrared brightness temperature increased rapidly, which indicated the formation of strong convective cloud cluster. The clear shadow at the southeast boundary of cloud body indicated the strong development of cumulonimbus cloud. Under the background of large-scale weather system, the important characteristic indexes obtained from in-depth analysis of mesoscale system can be used for the short term forecast and warning of severe convective weather.

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.

Based on the multiple remote sensing data from satellite and rice yield, the temporal and spatial distribution of drought was monitored in five provinces of the middle and lower reaches of the Yangtze River (MLRYR) in 2012 and 2013 by using the multiple drought indexes including precipitation condition index (PCI), vegetation condition index (VCI), soil moisture condition index (SMCI), temperature condition index (TCI) and optimized vegetation drought index (OVDI). And on this basis the applicability of five drought indexes in this area was contrasted by taking standardized precipitation index (SPI) and reduction rate of crop as reference. The results show that PCI and SMCI were more suitable to monitor the drought, while TCI and VCI weren’t suitable to monitor the drought alone in five provinces of the MLRYR. The drought with different levels occurred in five provinces of the MLRYR in 2012 and 2013, and the drought in 2013 was more serious (the range of drought was wide and the frequency was high) than that in 2012. The drought mainly occurred from January to February and June to August of 2012, and the drought region with NE-SW strip distribution concentrated in the north of five provinces of the MLRYR. However, the drought was mainly occurred from January to February and June to October of 2013, and the drought covered the whole area, but the drought situation in each province wasn’t synchronous.