Variation in Growing Season Thermal Resources in Central-East Poland

The work assesses heat resources in central-east Poland (2001-2019). As a measure of heat resources, the concept of growing degree days (GDD) was used. GDD is a useful tool for agriculture as it takes into account the aspects of local weather and, based on it, plant development can be predicted. Daily maximum and minimum air temperatures were used to calculate GDD at 7 stations using threshold base air temperatures of 0°C (commencement of the warm season) and 5°C (start of the period of active plant growth). The following basic characteristics of the distribution were calculated: arithmetic mean, minimum and maximum values as well as coefficient of variation. The direction and significance of changes of the heat resources were determined on the basis of linear trend equations. The significance of directional coefficient of the trend was estimated with t-Student test at the significance level of α = 0.05. The average air temperature during the growing season ranged from 14.6°C in Białystok and Białowieża to 15.6°C in Włodawa, its greatest increase being recorded in Włodawa and Siedlce (by 0.36°C per year). GDD increased from north to south in the study area, but the mean GDD varied considerably from one location to another. GDD0 and GDD5 showed an upward trend over the 2001-2019 period for the study region as a whole