Abstract: High relative humidity and temperature extremes can occur simultaneously and persist for periods of time, resulting in severe harm to human health. Here, in the case of the Jialing River basin, we use air temperature and relative humidity from the observed datasets to construct the apparent temperature, and then calculate heat wave indexes and cold wave indexes, so as to evaluate the temporal and spatial distributions and risk characteristics of heat and cold waves. The results show that in the period of 1960 to 2020, the heat waves took an increasing trend, while the cold waves took a significant decreasing trend. The apparent heat wave index was approximately 2-3 times of the corresponding heat wave index, but the apparent cold wave index was slightly greater than the corresponding cold wave index. This indicates that a high relative humidity can amplify the severity of the effect imposed by a heat wave or cold wave event, and the amplification in the heat wave case is greater than that of the cold wave. Through return period analysis, we find the heat (cold) wave severity based on univariate air temperature is severely underestimated owing to the ignorance of relative humidity.

Key words: relative humidity, heat wave, cold wave, apparent temperature, Jialing River basin