The humidity conditions and atmospheric drought risk in Poland in 1966-2020

Increasing air temperature is the factor causing relevant changes in humidity conditions in the long-term perspective. The growth of saturation water vapour pressure impacts the essential changes in relative humidity and saturation deficit, mostly in the warmer half of the year. As achieving a saturation state is advantageous for precipitation and cloud formation, the saturation deficit strengthening will disrupt these processes. Therefore, the drought indices were used to verify the frequency of dry months and the intensity of atmospheric droughts. The Standardised Precipitation-Evapotranspiration Index (SPEI), thermal-precipitation index (also called Ped index) and Sielianinov index were calculated using the air temperature and precipitation from April to September from the Polish Institute of Meteorology and Water Management – National Research Institute database for 46 measurement stations in Poland in 1966-2020.

The results for drought indices vary, but in a wider perspective, they point to spatial differentiation in the possibilities of droughts occurring and their intensity. The highest frequency in atmospheric drought is detected using the Sielianinov index. On the other hand, the Ped index points to the increasing frequency of drought throughout the year. Using the SPEI, the frequency of drought is similar. The trends in the indices are also varied, but there are some relevant similarities. In all of Poland, there are drying trends in April, which is caused by the relevant increase in the air temperature then (Ustrnul et al. 2021). From June to August, a visible drying trend is observed in Central and Southern Poland. The previously mentioned observations formed the basis of the drought risk regionalisation, which consists of three regions: Northern, Central and Southern Poland. Northern Poland has 11 stations, where the frequency of dry months was lower, and the trends were weaker. In Central Poland (25 stations), there is a higher frequency in dry months, and there are prominent drying trends in April, June and August. So, the dry conditions are frequent, and these conditions are not very changeable. Stronger drying trends are observed in the region of Southern Poland (10 stations), but the frequency of dry months is lower than in Central Poland.

Regarding the results, Northern Poland is a region with quite stable conditions and a lower risk of droughts. Atmospheric drought is more frequent in Central Poland, which is unfavourable for the region with well-developed agriculture. In Southern Poland, the long-term changes in meteorological conditions lead to drying trends of the atmosphere. It might cause the limited supplies of water to the upper parts of rivers, disrupting the hydrological cycle, and then leading to soil and hydrological drought.

 

This research was funded by the National Science Center (NCN) (grant number 2023/51/B/ST10/01926)