The aim of the present research has been an attempt at evaluating the water requirements of plum trees over 2016-2050 in the Bydgoszcz region drawing on the forecast changes in temperature. The paper draws on the forecasting of mean monthly temperature for the Bydgoszcz region in 2011-2050 according to the climate change scenario for Poland SRES: A1B (Bąk, Łabędzki 2014). The water requirements of the plum tree have been determined based on the indispensable precipitation determined by Kemmer and Schulz. The water requirements were calculated for the period January through December and May through September for each year in the 35-year period (2016-2050). The reference period was made up by a 35-year period immediately preceding it (1981-2015). In 2016-2050 in the Bydgoszcz region, in the light of the forecast temperature change scenarios, one should expect an increase in the water requirements of the plum tree. The annual (January-December) optimal total precipitation determined according to the Kemmer and Schulz method will increase for the plum tree from 712 mm to 807 mm (by 95 mm, which accounts for 13%). The optimal precipitation trend equations show that in the reference period (1981-2015), calculated, drawing on the Kemmer and Schulz number, the optimal annual precipitation was increasing in the plum tree in each pentad by 7.1-7.5 mm. In the forecast period (2016-2050) the water requirements will increase, however, in each pentad within a much smaller range, from 2.6 to 3.0 mm. In the summer period (May-September) determined by Kemmer and Schulz, the total precipitation optimal for the plum tree, expressing water requirements, in 2016-2050 will increase by 47 mm.