Increasing Extreme Temperature Events in the Guwahati City During 1971–2010

Abstract

Extreme temperatures are changing worldwide together with changes in mean temperatures. This study investigates the daily maximum and minimum temperatures of Guwahati city of Northeast India for different intensity and frequency indices for the period 1971–2010. The trends were estimated by linear regression technique and statistical significance of the trends was determined by Kendall’s tau statistic. Annual mean indices of extreme temperature events, viz, hottest day, hottest night, and coldest night showed increasing trends while coldest day showed decreasing trend. All frequency indices of hot events showed increasing trends while that of the cold events showed decreasing trends. Number of days above 35 °C is increasing significantly. On the other hand, number of nights above 25 °C is increasing while the number of nights below 10 °C is decreasing. Monthly intensity and frequency indices of hot and cold events during two sub-periods of 1971–1990 and 1991–2010 relative to the mean of the entire period (1971–2010) showed that the hottest day temperature was lower in the months of February, March, and April during 1991–2010 while in other months it was higher than the 1971–1990 sub-period. On the other hand, hottest and coldest night temperatures are more during the recent period. Similarly, both the number of hot days and hot nights showed increase in frequencies while number of cold days and cold nights showed decrease in frequencies in almost all months.