Climate change detection and annual extreme temperature analysis of the Irtysh Basin

As the largest tributary of the Ob River, the Irtysh River is an international river partially joining the territories of China, Kazakhstan, and Russia. Four meteorological stations in the Irtysh Basin were selected and the long-term observed daily temperature data were collected. The extreme temperature change was analyzed considering climate change. Detected by the heuristic segmentation by histogram comparison approach, climate was changed during the first half of the 1970s in terms of the increased mean value and decreased standard deviation of the daily temperature series. The noticeable change of the monthly mean temperature was the warmer winter. After climate change, the annual maximum temperature was little changed and its series was not segmented. However, the annual minimum temperature was significantly changed in terms of the increased mean value by more than 2°C, so its series was segmented to the pre- and post-change point subseries. The generalized extreme value distribution was fitted to the annual extreme temperature and the parameters were estimated by the maximum likelihood method. The return levels for 10/50/100-year return periods estimated by the profile likelihood method were obtained for the annual extreme temperature. The probability of occurrence of the cold extremes was decreased after 1970s.