Investigation of long-term extreme temperature indices in a Humid subtropical climatic zone of the Subarnarekha river from 1951 to 2024

Climate change, combined with anthropogenic activity, accelerates the frequency and intensity of extreme events. Thus, the objective of the study is to understand the changing trends in air temperature and extreme air temperature indices over the Subarnarekha River Basin on an annual and seasonal basis. The study also examines the spatio-temporal variation in extreme temperature indices. The maximum and minimum temperature data are downloaded from the India Meteorological Department (IMD) from 1951 to 2024. A total of 12 extreme temperature indices, as defined by the ETCCDI (Expert Team on Climate Change Detection and Indices), are selected for the study. These indices are TX10p (cool days), TX90p (warm days), TN10p (cool night), TN90p (warm night), SU (summer days), TR (tropical night), TXx (hottest day), TNx (hottest night), TNn (coldest night), WSDI (warm spell duration indicator), and CSDI (cold spell duration indicator). A significant temperature trend is assessed at the 0.05 level of significance. The result indicates that the trend of minimum temperature (from 0 °C to > 0.1 °C) of the basin increases more rapidly than the maximum temperature (from − 0.05 °C to 0.01 °C). Consequently, the difference between the maximum and minimum temperatures is decreased. We also observe that temperature changes are more pronounced at the seasonal level. The highest temperature increases are observed in the monsoon and post-monsoon seasons. The result also shows that of the twelve extreme air temperature indices, only four (TX10p, TN90p, TR, and TNn) show positive trends, while the remaining indices show negative trends.