Long-term trend of surface relative humidity in Hungary

Abstract

The long-term trends of relative humidity and its relationship with the long-term change of temperature are some of the unsolved problems of climate research. In this paper, the results of the analysis of long-term changes (1961–2020) in relative humidity and temperature in Hungary are presented. Homogenized station data series were used to perform the analyses. While warming was significant in each season, a significant reduction of relative humidity was observed only in spring and summer. The seasonal variability in the dependence of the change of relative humidity on the change of temperature indicates that the change of temperature directly impacts the change of relative humidity in summer, and the enhancement of evaporation due to the increase of temperature may mitigate the impact of warming in other seasons. Homogenized datasets were used to study the daily variation of the long-term trend of relative humidity. Significant reduction was found at noon in each season, except for autumn. However, the reduction was more scattered during the night, depending on the season and/or the geographical location of the station. The relationship between the surface data and data observed by radio sounding (00 UTC and 12 UTC in time period of 2007–2018) was studied to predict the long-term trends of relative humidity in the lower, 100-m deep layer of planetary boundary layer from the trend of surface relative humidity. The results suggest that this prediction can be reasonable only if daytime trends are considered.