Fig. 2

Annual frequency and HWII of heat waves identified from 1971 to 2015 in the studied areas. a Box plot for annul frequency of heat waves; b Box plot for HWII of heat waves; The boxes present the 25-to-75 percentile, whiskers (i.e., the horizontal dashes linked to boxes by vertical lines) present the 10-to-90 percentile, hollow square and thick dash in boxes are mean and median values. c Annual frequency and annual average HWII of heat waves over time; d Probability distribution fittings for annul frequency of heat waves, which are Poisson distributions, the λ refers to the vector of (non-negative) means. e Probability distribution fittings for HWII of heat waves, which are Gamma distributions, the α and β refer to the shape and scale parameters. All probability distributions have passed the Chi-square test considering a p value of 0.01