IMPACTS OF CLIMATE VARIABILITY ON RIVER ICE PHENOLOGY OF NINGXIA-INNER MONGOLIA REACH IN THE UPPER YELLOW RIVER

The Ningxia-Inner Mongolia Reach in the upper Yellow River in China suffers most serious ice related problems during winter. The high sensitivity of river ice to exterior conditions as well as the frequent extreme ice disaster events make it necessary to predict the evolution tendency and explore the response mechanism of river ice so as to deal with the potential threats in a changing climate scenario. In this study, we collect the historical hydrological and meteorological data (from 1954 to 2013); use both the Mann-Kendall trend detection and the Pettitt change point test to identify the trends and changes in river ice phenology. Results indicate: (1) the air temperature increases at the average rate of 2.19 degrees C/50 years along the overall river reach; (2) the timing of earliest ice-drift delays 8.1 days/50 years, that of earliest freeze delays 4.9 days/50 years, that of earliest breakup advances 26.9 days/50 years, resulting in the decrease of freeze duration of 7.1 days/50 years; (3) the ice thickness becomes thinner at the average rate of around 0.6 cm/year, and the freeze length can intuitively be assumed smaller; (4) the river ice characters all correspond well with the air temperature, and change points of them exist within mid-1980s.