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Based on the ERA5 reanalysis dataset, we analyzed the changes in extreme climate indices on the MP from 1981 to 2020, and the relationship between the extreme climate indices and atmospheric circulation indices. The results showed that (1) for temperature, (a) in terms of hot events, the inter-annual variation trends of summer days, warm days, and warm nights have significantly increased across the entire MP, with the central region experiencing a higher probability of extreme hot events. The inter-decadal variation of extreme hot indices showed a considerable increase from the period of 1991 to 2000 to the period of 2001 to 2010. (b) In terms of cold events, a substantial decrease in extreme cold events was revealed, with a great decrease from the period of 1981 to 1990 to the period of 1991 to 2000. (2) For precipitation, there was a decrease in extreme wet indices from 1981 to 2020. The simple precipitation intensity index (SDII) and total precipitation in wet days (PRCPTOT) exhibited a significant descending trend in the northern and northeastern MP. Decadal variations showed a decrease in extreme precipitation events, with a significant decline observed between the period of 1991 to 2000 and the period of 2001 to 2010. (3) For the relationship between the extreme climate indices and atmospheric circulation indices, extreme temperature indices are likely influenced by polar vortices, with the Asian polar vortex area index (APVAI) negatively correlated with extreme hot indices and the Asian polar vortex intensity index (APVII) positively/negatively correlated with most extreme hot and cold indices. Asian zonal circulation index (AZCI) showed significant correlations with most extreme hot and cold indices. Extreme precipitation indices only showed significant negative correlations with the Atlantic Meridional mode (AMM). [ABSTRACT FROM AUTHOR]

Based on the precipitation records of 2474 meteorological stations, this study investigated precipitation characteristics and trends in China from 1961 to 2010, including spatiotemporal distribution and changes in average annual precipitation amount, number of days when daily precipitation > = 1, 5, 10, 25, 50 mm, and extreme precipitation indices. The results showed that: (1) in terms of annual average precipitation amount, both dry to wet, wet to wetter, and shifting between wet and dry showed decadal and climatical fluctuations in annual precipitation totals in space and time, with a clear shift in space from the 0 to 200 mm and above 400 mm precipitation levels to the 200 to 400 mm precipitation level. (2) In terms of graded precipitation days, three kinds of trend changes were observed: (a) enhancement, manifested as an increase in precipitation events, mainly in the northwest and northeast of China; (b) reduction, manifested as a decrease in precipitation events, mainly in the central parts of China; and (c) polarization, which is manifested as a decrease in gentle and light precipitation events but an increase in dry days, heavy, and rainstorm precipitation events, primarily along coastal area in southeast China. (3) In terms of extreme precipitation events, precipitation persistence showed a decreasing trend, but an increasing trend in precipitation intensity and magnitude in most regions of China. This paper also presents the relationship between certain atmospheric circulation indices and the seasonal precipitation of summer and winter. The distribution characteristics and changes in minor precipitation events were highlighted, including gentle and light rain events. Relevant findings can provide scientific guidance for water resource management and conservation. [ABSTRACT FROM AUTHOR]

The long-term variability of direct and diffuse solar radiation at the surface remains unknown for many areas of the world due to the lack of measurements. In this study, two methods, an empirical model and a neural network, are used to estimate annual direct and diffuse solar radiation in North China for the 1959–2016 period. Results reveal that the two methods have a good performance in estimating direct solar radiation (R2 = 0.49–0.95), and the estimation accuracy of diffuse solar radiation can be improved by incorporating the influence of aerosols (R2 = 0.29–0.79). Generally, total and direct solar radiations have significantly decreased with the declining trend in sunshine duration since 1959 (p < 0.01). However, diffuse solar radiation shows a significant (p < 0.01) increasing tendency over the period of 1959–2016. The proportions of direct and diffuse solar radiation are almost equal from 1982 onward. Influenced by the atmospheric aerosols, two periods with large diffuse solar radiation values have been observed from 1959 to 1989 and from 2004 to 2016. Over the period of 2000–2016, sunshine duration and aerosols can explain 89 and 85% of direct and diffuse solar radiation variations, where aerosol concentration accounts for about 63% of changes in diffuse solar radiation. This study characterizes the long-term variability of direct and diffuse solar radiation in North China since 1959 and highlights the significance of aerosols to diffuse solar radiation from 2000 to 2016. [ABSTRACT FROM AUTHOR]