Based on gridded temperature data from the China Meteorological Administration (CMA), two types of methods, i.e., absolute methods and relative methods, respectively, were used to identify heat waves in Mainland China. Four statistical indicators, including the occurrence frequency, duration days, earliest occurrence date, and latest extinction date, were constructed to analyze the spatial-temporal characteristics of heat waves, especially on the annual and decadal change trends. Firstly, we found that both the frequency and the duration of heat waves decreased in the period from 1960 to 1989 but increased in the 1990s and increased significantly from the early 2000s to the 2010s. Spatially, the frequency and the duration obtained by each type of method are significantly different among different regions when considering different facts, such as different regions that have different degrees of tolerance to heat waves. Secondly, the decadal distribution characteristics of the earliest occurrence date and the latest extinction date of heat waves well capture the hot summer, the stronger sensitivity of winter to warming than other seasons, and the gradually increasing intensity of heat waves. It provides a multidimensional reference for the cause analysis and prediction of extreme heat waves in China.

High-quality measurements of air quality are the highest priority for understanding widespread air pollution. Visibility has been widely suggested to be a good alternative to PM_2.5 concentration as a measure. In this study, the similarities and differences between visibility and PM_2.5 measurements in China are checked and the results reveal the potential application of visibility observation to the study of air quality. Based on the quality-controlled PM_2.5 and visibility data from 2016 to 2018, the nonparametric Spearman correlation coefficient (ρ) values between stations for PM_2.5 and visibility-derived surface extinction coefficient (b_ext) decrease as the station distance (R) increases. Some relatively low ρ values (<0.4) occur in regions characterized by the lowest (background) levels of PM_2.5 and b_ext values, for example, the Tibetan and Yungui Plateau. The relatively lower ρ for b_ext compared to PM_2.5 is probably caused by the predefined maximum threshold of visibility measurements (generally 30 km). A significant correlation between PM_2.5 and b_ext is derived in most stations and relatively larger ρ values are evident in eastern China (Northeast China excluded) and in winter (the national median ρ is 0.67). The abrupt changes in specific mass extinction efficiency (α_ext) imply a potentially large influence of alternation of visibility sensors or recalibrations on visibility measurements. The b_ext data are thereafter corrected by comparison to the reference measurements at the adjacent stations, which leads to a three-year quality assured of visibility and b_ext datasets.

The rainfall distribution in southwest China is uneven, and the rainstorm threshold cannot use in a unified standard. This paper synthesizes a calculation method for the extremely heavy precipitation threshold and the provision of the rainstorm threshold in meteorological operation. It calculates the daily precipitation rainstorm threshold at 400 national ground stations in southwest China. The rainstorm events from 1961 to 2021 were statistically analyzed using the rainstorm threshold and analyzing the spatial-temporal variation characteristics. The results show that the number of single-station rainstorm events and the average precipitation of single-station rainstorm events in southwest China decreased from east to west. The number and frequency of single-station rainstorm events in Guizhou, Sichuan, Tibet, and Chongqing are increasing, while the number of single-station rainstorm events in Yunnan is decreasing. There is no apparent spatial distribution pattern for the continuous rainstorm events in the southwest region. From 1961 to 2021, the number and frequency of rainstorm events at a single station in southwest China followed an upward trend. The number of rainstorm events at a single station increased by 16.7 times · (10a)⁻¹, and the frequency of rainstorms increased by 9.9% · (10a)⁻¹. The continuous rainstorm events show an increasing trend, with an increase of 0.1 times · (10a)⁻¹. Using the rainstorm threshold in southwest China, the early warning threshold for rainstorm disasters can be adjusted. The temporal and spatial characteristics of rainstorm events since 1961 can analyze the changes occurring in rainstorm events under global warming and provide data to support the response of southwest China to climate change.