Effect of the forecast climate change on the apple tree water requirements in the Bydgoszcz region

The aim of the present research has been an attempt at evaluating the water requirements of apple 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 apple 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 the 2016-2050 period in the Bydgoszcz region, in the light of the temperature change scenarios, one could expect increased apple-tree water requirements. Determined with the Kemmer and Schulz method, the required annual (January-December) optimal precipitation will increase for the apple tree from 681 mm to 849 mm (by 168 mm, namely by 25 %). The optimal precipitation trend equations show that in the reference period (1981-2015), calculated with the Kemmer and Schulz numbers, the optimal annual precipitation for the apple tree was increasing in each pentad by 5.8-6.3 mm. In the forecast period (2016-2050) the water requirements will increase, however, in each pentad in a much greater range; from 8.5 to 9.6 mm. In the summer period (May-September) determined by Kemmer and Schulz, the optimal precipitation, expressing the water requirements, for the apple tree in 2016-2050 will increase by 84 mm.