1999年夏季中昆仑山北坡诸河冰雪大洪水及其成因分析

Extreme Flood Events in 1999 and Their Formation Conditions in Northern Slopes of the Middle Kunlun Mountains

1999年盛夏中昆仑山北坡大多数河流出现了有正式水文记录以来的最大洪峰,各河流最大洪峰出现时间存在不一致性,洪峰变化复杂.应用主要河流出山口水文站的逐日流量和降水量,和田气象站的逐日0℃层高度,500 hPa气温以及NCEP/NCAR 500 hPa高度场资料,分析了1999年夏季中昆仑山北坡诸河出现的历史特大洪水特性及其气象成因.这次特大洪水是高空持续高温引起的冰雪融水与产流区出现的暴雨共同作用下的混合型洪水.洪水前期春季到初夏该区域山区降水偏多,高空气温和0℃层高度持续偏低,对高山区的积雪积累极为有利;7月底至8月初和田高空气温和0℃层高度迅速上升并维持数日,使冰雪快速消融,同时山区出现大降水是引发洪水的直接气象成因.在青藏高原东部柴达木盆地上空存在有500 hPa稳定高压,使中亚副热带大槽东移中昆仑山北坡是这次特大洪水发生的环流系统特点.

The Super-flood and its cause of the rivers on the northern slopes of the Middle Kunlun Mountains in 1999 is analyzed, using the daily runoff and precipitation of hydrological stations, the 0 ℃ level and 500 hPa temperature of Hotan meteorological observation, and the height field of NCEP/NCAR. The flood peak in 1999 is the maximum in the instrumental records. It was a medley flood caused of snow-ice melting water and heavy rain. The precipitation from spring to early summer was more then the average. The 0℃ level and 500 hPa temperature were lower than the average.Snow cover was deeper. The 0 ℃ level and 500 hPa temperature increased rapidly from the end of July to the early August, and then lasted a few days. The ice and snow were melting rapidly. At the same time, a heavy rain occurred in the mountains. The circulation system causing the flood was characterized by a high press located upon the Qaidam basin of the northeast Tibetan Plateau and a trough of Central Asia moved eastward to the northern piedmont of the Middle Kunlun Mountains.