中国西北干旱区流域洪水的形成机制及时空变化特征

Mechanisms and spatiotemporal variation characteristicsof flooding over northwestern China

中国西北干旱区的自然地理特征和水文气候条件导致了复杂多变的流域洪水形成机制。在全球和区域气候变化影响下,该地区流域洪水的年际变化特征及驱动机制仍不明确,制约了重点区域防洪减灾以及“一带一路”倡议的实施。本文基于中国西北干旱区58个流域1961—2017年实测年最大洪峰量级系列,借助统计检验和机器学习聚类方法,分析并揭示了该地区过去近60年流域洪水的形成机制、空间格局及年际变化特征。研究发现中国西北干旱区流域极端洪水频次和年最大洪峰量级均呈增加趋势,极端洪水频次最大增幅约0.84次/10a,年最大洪峰量级相较于多年平均值最大增幅约29%/10a,增幅较大流域主要位于天山东部和祁连山地区。西北地区流域洪水成因主要可分为暴雨型、融雪型和混合型3种,其中暴雨型和混合型洪水频次呈增加趋势,融雪型洪水频次呈减少趋势。洪水成因转换对年最大洪峰量级增加贡献最高可达38%,显著高于由单一水文气象要素变化对洪峰量级变化的贡献程度。研究结果强调从成因机制转变角度开展地理环境复杂地区流域洪水预测及变化归因的重要性。变化环境下的工程水文设计需要考虑洪水成因导致的洪水样本非一致特征对洪水频率分析的影响,从而为流域洪水风险管理及应对提供科学支撑。

The physical geography and hydroclimatic conditions in the arid region of in northwestern China leading to diverse flood-generation mechanisms.Under the influence of global and regional climate change,the spatiotemporal variation of floods and flood-generation mechanism in this region is still unclear and restricts flood prevention and mitigation and the implementation of the Belt and Road Initiative in the major regions.Based on the series of the annual maximum flood peak discharge in 58 river basins in the study area from 1961 to 2017,we analyzed and revealed the mechanisms,spatial distribution and interannual variation characteristics of flood in the basin in the past 60 years based on statistical tests and machine learning approaches.The results show that the frequency of extreme floods and the annual maximum flood peak discharge magnitude are increasing,with the maximum increase in the frequency of extreme floods at about 0.84 times/10 years,and the maximum increase in the annual maximum flood peak discharge magnitude at about 29%/10 years compared with the multi-year average,and the largest increase is mainly observed in the eastern Tianshan Mountains and the Qilian Mountains.There are three main flood generation mechanisms,i.e.,rain(R),snow(S)and mix(M),the frequency of R and M floods increased significantly,while the frequency of S floods decreased.The contribution of flood mechanisms transformation to the increase of annual maximum flood peak discharge magnitude can reach up to 38%,which is significantly higher than the contribution of a single hydrometeorological factor such as precipitation.The results of this study emphasize the importance of attributing and predicting the changes of flood characteristics in geographically complex region from the perspective of flood mechanisms.Engineering hydrological design in the changing environment also needs to consider the influence of the heterogeneity of flood samples caused by different flood mechanisms on the flood frequency analysis,so as to provide scientific support for flood risk management and response in the basin.