以秦岭南北的汉江上游、渭河为例,对比分析了万年以来洪水发生的时间、流量的差异,并探讨了气候变化与洪水发生的联系。结果表明:在长时间尺度上,秦岭南北的汉江上游、渭河均有古洪水事件的沉积记录,汉江上游的洪水流量远大于渭河流域的洪水流量,洪水发生时间主要集中在4200~4000 a BP和3200~3000 a BP这两个时间段内;对季风气候变化分析表明,4200~4000 a BP和3200~3000 a BP是季风突变气候恶化的两个转折期,气候突变使得秦岭南北河流在这个时间段均有古洪水事件记录,但因测年分辨率的限制,似乎秦岭南北洪水发生时间具有一致性。在短时间尺度上,对秦岭南北实测洪水分析发现,虽然大多数年份秦岭南北没有洪水同时发生,但在个别年份内秦岭南北还是有洪水同时发生情况;从华西秋雨角度分析表明,秦岭南北的汉江上游、渭河处于华西秋雨核心区,但因多种因素的影响,在多数情况下秦岭南北洪水发生的时间并不都是完全相同。研究成果有助于从水文学角度在长时间尺度上揭示秦岭南北地区主要河流洪水发生规律,深化特大洪水事件与季风气候的关系;同时也加深了对秦岭地理分界作用的认识,对秦岭南北因地制宜的进行防洪减灾和水资源的合理调度开发有重要的实践意义。
英文摘要:
The upper reaches of Hanjiang River and Weihe River in the northern and southern regions of Qinling Mountains were significant climate zone in China. The northern region of Qinling Mountains located at zone of the temperate monsoon climate where the annual precipitation varies between 400 mm and 600 mm regionally, and 70% of precipitation occurs in form of rainstorm between June and October. The upper reach of Hanjiang River is situated in the humid zone with a subtropical monsoonal climate. The mean annual precipitation is 830-900 mm,which is brought by the southeastern and southwestern maritime monsoon. Lots of researches including characteristics of temperature change,effects of different disaster inducing factors had been taken in those areas,while few research about the rule of longtime scale flood. Then the upper reaches of Hanjiang River and Weihe River in the northern and southern regions of Qinling Mountains were chosen to study comparatively on floods time,discharge and its relationship with climate change in different timescales. The study result showed that the palaeoflood events were identified in the upper reaches of Hanjiang River and Weihe River in the northern and southern regions of Qinling Mountains,and the palaeoflood discharge in the upper reaches of Hanjiang basin were bigger than those in Weihe in longer timescale. And the palaeoflood events happened mainly in 4 200- 4 000 a BP and 3 200-3 000 a BP,the facts of the occurrence of extraordinary floods suggest that the climate with highly unstably and variable in the region. Climatic variability resulted in an increased frequency of extreme hydroclimatic events in the semi-arid and subhumid regions. However,because of low dating resolution,the difference of flood time in the upper reaches of Hanjiang River and Weihe River could not be achieved. While in short timescale of observed floods,the upper reaches of Hanjiang River and Weihe River were the center of the autumn rains in West China,due to the influence of many factors for the autumn rains in West China,most of the flood time was asynchronous in the most years in the upper reaches of Hanjiang River and Weihe River except the floods of 1983,2005 and 2011. This had proved that climate change macroscopic region would cause floods events in the northern and southern regions of Qinling Mountains. It is suggested that this study results would not only contribute to the better understanding the rule of flood events,and from hydrological point,revealing the relationship between flood events and monsoon climates in the northern and southern regions of Qinling Mountains, but also provide significant data for flood hazards mitigation,development and water resource utilization in local condition in the northern and southern regions of Qinling Mountains.