Summary:

The aim of this study to estimate the water demand for spiked speedwell (Veronica spicata L.) on a green roof in Bydgoszcz urban aglomeration, depending on projected climate change. A scenario of climate changes for Poland SRES: A1B was taken into account. Water needs of spiked speedwell were determined by the method of plant coefficients. Based on adopted assumptions and performed calculations, it was found that in the forecast period (2021-2050) there will be greater variability in the water needs of the spiked speedwell. In the forecast period, a clear tendency towards increasing water needs of the spiked speedwell is expected every 6.9 mm in a decade. The total rainfall shortages are expected to decrease for the entire growing season of the spiked speedwell (11. May - 10. July). Those water shortages decreased - in an average, moderately dry and very dry year, respectively - from 129.9 mm, 175.7 mm and 210.7 mm in the reference period to 121.2 mm, 169.4 mm and 205.5 mm in the forecast period.