Long-Term Changes in the Relative Humidity in Poland in 1966–2020

Abstract

The main purpose of this paper was to identify significant changes in air moisture conditions in Poland, which accompany climate warming. Meteorological data used in the research included the relative humidity (RH) values from 48 stations obtained from the Institute of Meteorology and Water Management—National Research Institute from 1966 to 2020. The monthly mean, standard deviation (SD) and coefficient of variation of RH from 12 PM for all months (with particular reference to the middle months of seasons—January, April, July and October) were used. Additionally, the dry weather (RH < 30%) frequency in the warm half of the year was observed. Long-term changes were found by comparing relative humidity values in three 15-year subperiods (1966–1980, 1986–2000 and 2006–2020) and the statistical significance was estimated using the Mann-Kendall test. The most considerable long-term changes were noticed in April and July, especially in the last 15-year subperiod. The statistical significance was higher, mostly in warmer months. The SD was also higher in April and July than in January and October. Hence the humidity conditions in the warmer half of the year fluctuated more and more widely. A significant decrease in the RH mean values and an increase in SDs in spring and summer impact the increasing frequency of dry weather. Relations between meteorological characteristics suggest the warming climate contributes to drying the near-surface atmosphere but also impacts intensive precipitation events or snow cover parameters. The decreasing trend of long-term relative humidity may negatively impact the environment, human health and well-being and cause serious economic losses.