One effect of global warming is the increasing risk of drought. The shortage of water in the soil has a direct impact on crop plants. It can therefore be expected that drought stress will negatively affect forests. The aim of this study was to determine the length of the drought in the forests of Poland in 2015. Calculations were carried out using data from 21 meteorological stations for the conditions prevailing in the reference stand, which was determined to be a middle-aged pine stand growing on poor sandy soils classified as Dystric Arenosol. Drought was treated as the state when the soil water available to plants is depleted up to a depth of one meter. Daily changes in soil water storage were measured on the basis of the balance of water inflow-outflow. Climatic water balance was also determined. The calculations of the soil water storage deficit for the conditions of the reference forest ecosystem showed that in 2015 drought soil occurred in almost all of the forests of Poland. Wielkopolska was affected by the earliest-starting and longest-lasting drought. To a lesser extent, however, it extended throughout all of central Poland, from the west to the eastern border of the country. This is where one could expect to see the negative effects of the lack of water available to trees, which can be manifested as a smaller increase in growth, a decrease in health status, and – in particularly unfavorable conditions – dying trees. The climatic water balance showed that the annual water deficit in Wielkopolska exceeded 100 mm.