Summary:

This paper attempts to evaluate expected climate changes for the purpose of irrigating plants using the hydrothermal index of Sieljaninov (HTC). Air temperature and total precipitation were simulated for conditions current and expected for a chosen meteorological station in Central Poland, according to the GISS Scenario, HadCM3 and GFDL (which is typical for Poland assuming the CO2 concentration doubles, as is expected for the years 2050-2060). Four 500-year daily temperature and rainfall series were used for computing the hydrothermal index of Sieljaninov, with a 30-day window for irrigating periods, from April to September. The simulated hydrothermal index was presented on a graph during the vegetation period as a course of means, with critical area, standard deviations and probabilities of medium dry, dry, very dry and extremely dry periods.
The presented results show changes of average hydrothermal index (up to a 30 per cent drop) in considered periods and scenarios, as well as a 15 per cent variance increase (except GISS scenario). During the four critical months of the year, the estimated probability of extremely dry periods occurring (HTC<0.4) shows two, three and four times the risk of drought for the GISS Model E, HadCM3 and GFDL-R15 scenarios respectively.