冰冻圈水文过程对黑河上游径流的影响分析

黑河上游处于高寒山区,开展冰冻圈水文过程对径流的影响研究,对于判断该地区径流变化趋势及其可持续性具有重要意义。本文应用基流分割、逐步多元回归等方法,分析了1960—2013年黑河上游出山径流量的变化及其原因,重点估计了融雪、冰川融化对径流的贡献,探讨了土壤冻融过程对径流变化的可能影响。分析结果表明,黑河上游山区河川径流在近54年间呈现上升趋势,其中以基流部分的上升为主。降水与气温变化对河川径流上升均有较大贡献。导致春季径流增加的主要因素为温度、降水次之;导致秋季径流增加的主要因素为降水、温度次之。夏季黑河上游东支的雨强有显著增大趋势(日雨量增幅为0.9 mm/10 a),对于河川径流贡献的比例约为15%。黑河山区的逐年降雪量变化不显著,冰川融化对径流增加的贡献小于10%。由此推断气温上升导致基流增加的主要原因是:气温升高导致高寒山区冻土活动层增厚,增加了土壤蓄水容量,从而导致降雨下渗量增加和基流量增大。由于黑河上游冻土分布广泛,未来气温持续上升的情况下,这种产流机制变化导致的基流增加具有可持续性。

Impact of cryosphere hydrological processes on the river runoff in the upper reaches of Heihe River

The upper reach of the Heihe River is located in alpine mountain area, exploring on the effect of the cryosphere hydrological process on runoff is of significance to diagnose the change of runoff and its sustainability. This study uses a method of base flow separation and a stepwise multiple regression model to investigate the reasons for the runoff changes in the upstream of Heihe River during 1960-2013. The contribution of snowmelt and glacier melt to runoff is particularly estimated to explore the possible influences of soil freezing and thawing on runoff changes. The results show an increasing trend of the total runoff from the upper reach in the past 54 years,dominated by the changes in base flow. Changes in precipitation and air temperature had great contribution to the increasing runoff. In spring,the dominant factor causing the increasing runoff was the air temperature rather than the precipitation; while in autumn,precipitation was the dominant factor rather than air temperature. In summer,rainfall intensity had a significant increasing trend (daily rainfall increase of 0.9 mm/10 a) in the east branch of the upper reach, which contributed to runoff by about 15%. Changes of snowfall in mountainous region were not significant,and glacier melt runoff contributed less than 10% to the runoff increase. Therefore, the possible reason for the increase of base flow is rising temperature thickened the active permafrost layers, which leads to the increase of soil water storage capacity, and finally results in the increase of rainfall infiltration and base flow. Because of the wide distribution of permafrost in the upper reach, the increase of base flow caused by this change of runoff mechanism will be continuous in the future as the rising air temperature.