Impact of climate warming on the humidity properties of the temperate transitional climate – the case of Poland

In recent years the climate warming has been noticed in many regions worldwide. The increase in air temperature is held as the most significant symptom of climate change. However, the thermal properties of atmospheric air also impact other characteristics of atmospheric air, especially the moisture. Therefore, the impact of the increase in air temperature on the humidity characteristics will be shown in the case of the temperate transitional climate of Poland. The meteorological data from 1966 to 2020 from the Polish Institute of Meteorology and Water Management – National Research Institute measurement database were used. The analysis of the humidity change was based on the air temperature and relative humidity measurements from the noon hours in January, April, July and October. These data were also applied to the saturation and actual water vapour pressure calculations. The Mann-Kendall test was applied to the statistical significance verification, and the Theil-Sen slope was used to describe the long-term trends in the thermal and moisture characteristics.

The air temperature affects the maximum amount of water vapour possible to collect in the atmospheric air. It is defined by the saturation water vapour pressure, which is a function of thermal properties. Comparing the changes of saturation water vapour pressure in the long-term perspective, there is a significant increase observed in all seasons. Simultaneously, the higher the temperature, the more water vapour is needed to achieve the saturation state, which modifies the condensation processes and then precipitation formation. The long-term trends in humidity characteristics are dependent on their properties, and so they react in different ways to climate warming. The indices describing the level of saturation state, like relative humidity or saturation deficit, are sensitive to the modification of air temperature, so they change significantly due to climate warming. In spring and summer, the monthly mean of relative humidity decreased by almost 10% and the monthly mean of saturation deficit increased by about 5hPa in July in the long-term perspective. On the other hand, the actual water vapour pressure describes the real water vapour amount by the pressure it exerts on the ground. The trends in the actual water vapour pressure are not as clear as in the relative humidity, except for the coastal region where a slight increase is observed.

To conclude, climate warming is a significant process of climate change, which impacts other properties of the atmosphere. The thermal conditions have a relevant effect on the air moisture by decreasing the level of the saturation state. However, the real amount of water vapour in atmospheric air (described by the actual water vapour pressure) does not change as significantly as the relative humidity or saturation deficit.