Analysis of China's Haze Days in the Winter Half-Year and the Climatic Background during 1961–2012

The characteristics of haze days and the climatic background are analyzed by using daily observations of haze,precipitation,mean and maximum wind speed of 664 meteorological stations for the period of 1961–2012.The results show that haze days occur significantly more often in eastern China than in western China.The annual number of haze days is 5–30 d in most parts of central-eastern China,with some areas experiencing more than 30 d,while less than 5 d are averagely occurring in western China.Haze days are mainly concentrated in the winter half-year,with most in winter,followed by autumn,spring,and then summer.Nearly 20%of annual haze days are experienced in December.The haze days in central-eastern China in the winter half-year have a significant increasing trend of 1.7 d per decade during 1961–2012.There were great increases in haze days in the 1960s,1970s and the beginning of the 21st century.There was also significant abrupt changes of haze days in the early 1970s and 2000s.From 1961 to 2012,haze days in the winter half-year increased in South China,the middle-lower reaches of the Yangtze River,and North China,but decreased in Northeast China,eastern Northwest China and eastern Southwest China.The number of persistent haze is rising.The Longer the haze,the greater the proportion to the number persistent haze.Certain climatic conditions exacerbated the occurrence of haze.The correlation coefficient between haze days and precipitation days in the winter half-year is mainly negative in central-eastern China.The precipitation days show a decreasing trend in most parts of China,with a rate of around–4.0 d per decade in central-eastern China,which reduces the sedimentation capacity of atmospheric pollutants.During the period of 1961–2012,the correlation coefficients between haze days and mean wind speed and strong wind days are mainly negative in central-eastern China,while there exists positive correlation between haze days and breeze days in the winter half-year.The mean wind speed and strong wind days are decreasing,while breeze days are increasing in most parts of China,which is benefitial to the reduction of the pollutants diffusion capacity.As a result,haze occurs more easily.

Characteristics and Diagnosis of the Landfalling Tropical Cyclones in the Guangdong-Hong Kong-Macao Greater Bay Area of China During 1981-2018

This paper applies statistical and synthetic analysis methods to study the characteristics of the three types of tropical cyclone(TC) that landed in the Guangdong-Hong Kong-Macao Greater Bay Area(GBA) from 1981 to2018 and the reasons for the differences of TC-induced wind and precipitation. The results show that there are interdecadal changes in the frequency and intensity of the landfalling TCs in the GBA, with decreased frequency but increased intensity in the 2010 s. The TCs that landed in the west of the Pearl River Estuary(PRE) have the highest frequency and the strongest intensity during landing, which bring the strongest winds;the TCs that landed in the PRE have the lowest frequency and the shortest duration after landing, which cause the strongest precipitation;the TCs that landed in the east of the PRE have the longest duration on the land. This study shows that near the center of the TCs that landed in the PRE, there is a weak anomalous cyclonic shear compared with the ones that landed in the west of the PRE. It is a confluence area of anomalous north wind and anomalous southwest wind, with better water vapor convergence and dynamic rising conditions, which is conducive to the formation of heavy precipitation.Compared with the TCs that landed in the PRE and in its east, there is a closed positive anomalous center of pressure gradient in the northwest center of the TCs that landed in its west, resulting in higher wind speeds in the west of the PRE. The characteristics of the three types of TCs in the GBA are highly related to TC-induced damage.In the future, the GBA needs to focus on preparing for TCs landing in its west. Zhuhai, Jiangmen and Huizhou are key cities to guard against TCs. The results of this study provide foundations for effective management and reduction of TC disaster risks in the future development of the GBA.

Climate services for addressing climate change: Indication of a climate livable city in China

China, like many countries, is under great pressure to reduce climate change and adapt to current situations while simultaneously undertaking economic development and transformation. This study takes advantage of climate opportunities and provides a new concept and mode of urban climate services in order to address climate change. Eighteen indicators based on climate and climate-related variables were used to provide an assessment, in the form of an index, of how livable a city is depending on prevailing climatic conditions. The resulting index can also be used to investigate how recent and future changes in the climatic conditions could affect livability. All Chinese cities and regions share the common goals of promoting low-carbon development, improving resilience against climate change, and integrating economic growth with climate actions. Climate services have been developed in China to provide decision-makers this measure of livability. Such a move facilitates sustainable development alongside economic growth by aiding government efforts in climate adaptation and low-carbon development. Our approach represents multidisciplinary and demand-driven research on adaptation to and the impacts of regional climate change, thereby transforming climate science into a climate service and ensuring that climate information can be provided in a scientific, practical, and customized way for policy-makers. The outputs can be used locally to take concrete climate actions and integrate climate services into decision-making processes.