The severity of heat and cold waves amplified by high relative humidity in humid subtropical basins: a case study in the Gan River Basin, China

Abstract

High relative humidity (RH) and temperature extremes can occur simultaneously and persist for periods of time, resulting in serious harm to human health, especially in humid regions. Here, in the case of the Gan River Basin, we used air temperature and RH from the observed and ERA5 reanalysis datasets to construct the apparent temperature and investigate the characteristics of heat and cold waves. Heat waves showed the increasing trends from 1961 to 2018 (particularly from 1997 to 2018), whereas during the same period, cold waves showed the significant decreasing trends. In general, ERA5 reasonably reflected the spatiotemporal characteristics of heat and cold waves, and the ability to simulate cold waves was slightly greater than that of heat waves. The amplifying effect of high RH on heat waves was significantly greater than on cold waves. The increasing rates of heat waves in ERA5 at the mild, moderate, and severe grades were slightly greater than the observations. Cold waves at various grades showed significant downward trends, and the decreasing rates of cold waves in the observations were slightly greater than those in ERA5. Using an analysis of the return period (occurrence probability), traditional univariate risk assessment methods based on maximum or minimum temperature may substantially underestimate the risk of extreme events, such as the 2014 heat wave and the 1969 cold wave, because the effects of RH were ignored.