Spatial-temporal Differentiation of Sauna Days with Different Intensities in China from 1961 to 2017

Sauna weather with high temperature, high humidity and long standby time has become one of the main meteorological hazards faced by urban residents. Based on the daily maximum temperature and relative humidity datasets of 545 meteorological observation stations in China from 1961 to 2017, the spatial-temporal evolution characteristics of sauna days with different intensities in China were studied from three aspects: climatic state, trend and fluctuation characteristics, using the standard of sauna days defined by the Central Meteorological Observatory of China Meteorological Administration. The results showed that: firstly, the spatial pattern of sauna days with different intensities in China was high in southeast China and low in northwest China from 1961 to 2017, and the spatial pattern of sauna days with the same intensity in different research periods had little difference, which was in good agreement with the spatial pattern of sauna days with corresponding intensities in the whole research period. With the increase of intensity, the sauna days in China decreases gradually. Secondly, the trend of sauna days with different intensities in China was bounded by Hu Huanyong Line from 1961 to 2017, showing a pattern of increasing or decreasing mosaic in the southeast China and mainly decreasing trend, while the spatial differentiation pattern in the northwest China changed little. The trend of sauna days with different intensities in China increased significantly in 1991-2017 compared with 1961-1990. Thirdly, the fluctuation of sauna days with different intensities in China was bounded by Hu Huanyong Line, showing a spatial pattern of large fluctuations in the southeast China and small fluctuations in the northwest China. And the fluctuation of sauna days and heavy sauna days showed obvious threeblock distribution characteristics. The fluctuation characteristics of sauna days with different intensities in China from 1961 to 1990 and 1991 to 2017 were in good agreement with the whole research period. The fluctuation difference before and after 1990 mainly concentrated in the vicinity of Hu Huanyong Line and its southeast area, and the fluctuation differences increased mainly, indicating that the variation of sauna days with different intensities in the southeast China increased from 1991 to 2017.