Climate change impacts on Temperature-Humidity Index, (Case Study: Ramsar and Babolsar stations)

Rising greenhouse gases and the resulting increase temperature have disrupted the balance of the earth climate system. Combined increase in temperature and humidity above a certain threshold causes stress in livestock like dairy cows, which reduces milk production. To assess the effect of heat stress on livestock, a so-called temperature-humidity index (THI) is used. The aim of this study is to investigate the possible effects of climate change on THI in two stations located in north of Iran namely, Babolsar and Ramsar For this purpose, the projected values of THI under three climate change scenarios i.e. RCP2.6, RCP4.5, RCP8.5 were downscaled using SDSM weather generator. The results showed that there exist a significant positive trend in THI time series in both baseline (1961-2005) and future periods. According to results of this study, it is projected that number of days with heat stress would increase and more severe classes of THI will occur. The findings also indicated that the stress conditions in Babolsar have been more severe than Ramsar, such that, during the baseline period, Ramsar and Babolsar stations had 4 and 5 months of a year with heat stress , respectively, while it is projected that by the end of the century, these figures will increase to 6 and 7 months, respectively. Besides, the results showed that in the baseline period days with severe stress class (risk of mortality of dairy cattle) were not recorded in any of the studied stations, but for the far future period (2071-2100) in Ramsar and Babolsar stations, severe condition is projected to occur in two and six days of the year, respectively, which is a serious warning for the province's livestock industry.