Climatic water balance in the Gory Opawskie Landscape Park

This paper presents the analysis of the climatic water balance (KBW) in Góry Opawskie Landscpe Park, situated in the southern part of Poland. The research concerned Norway spruce forest stability disturbances against the rainfall conditions in the lower montane zone of the Jesioniki Massif. The data comes from weather measurements in years 1981−2018, which were collected at the three IMGW−PIB and one ČHMÚ meteorological stations. Detailed analysis concerned vegetation season from April to October. Multiannual average value of KBW index in whole vegetation period totalled to +220.5 mm (±175 mm). The lowest values were recorded in April (+20.3 mm on average), while the highest ones in July (+41.0 mm). The average ratio of the number of months with a positive climatic water balance to months with a negative balance equaled to 3.7. The probability of a month with a negative value of the climatic water balance is 20%. In the investigated period, months with negative values of climatic water balances occurred in almost 21% of the cases. In the analysed vegetation period the climatic water balance reached values below zero in years 1992, 1993, 2003, 2004 and 2015, which turned to be the lowest result (–129.7 mm, i.e. 159% below the climatic norm). Due to the high variability (σ2=2794.7 mm) of the climatic water balance and long−term periods with precipitation deficits in recent years, the phytoclimatic conditions do not promote the development of spruce forest vegetation in this area