Hydrological and geocryological response of winter streamflow to climate warming in Northeast China

An abrupt warming of regional climate with a 1.3 degreesC rise in annual air temperature, coupled with an increase of 20-40% in precipitation, has occurred in the 1990s in the permafrost region of Northeast China. The geocryological and hydrological responses of a river basin at high latitude and at altitude with some permafrost are detected based on monthly climatological and streamflow data for 40 years (1958-1998). The variation in depth of the active layer is estimated by an empirical model using annual air temperature, its annual amplitude and the maximum thickness of snow cover. Significant responses of winter streamflows to a 2.4 degreesC of air temperature warming during December to February were observed. This was especially true for the greatest warming (4.4 degreesC in February during the 1990s) when runoff increased by 80% in February and by 100% in March from the prior. These responses are caused by a change in depth and temperature of the active layer ranging from 1.5 to 3.0 m in areas where the drainage of the unfrozen water can occur when the ground temperature rises above 0 degreesC from -0.8 degreesC in February and March. The depth of the seasonal frost has shrunk by about 30 cm and the active layer thickness increased by about 40 cm in permafrost in the 1990s because of the warmer climate. The hydrological response from winter streamflows in permafrost areas is more significant and quicker than that from the seasonal frost areas. The freezing and drainage of ground water at 2.0-3.0 m deep in March is very sensitive to the climatic warming. (C) 2003 Elsevier Science B.V. All rights reserved.