城市化背景下年最大日径流演变及影响因素研究——以长江下游秦淮河流域为例

随着气候变化和人类活动的加剧,城市化地区水文过程受到较大影响,极端水文事件发生频率显著加大,探究城市化地区洪水演变和驱动机理对于防洪减灾具有重大意义。本文以长江下游快速城市化地区的秦淮河流域为例,分析了1987—2018年期间该流域年最大日径流的演变特征,构建多元线性回归模型和广义可加GAMLSS模型识别了关键驱动因子并量化其贡献作用。结果表明:(1)城市化背景下秦淮河流域年最大日径流呈现显著上升趋势,平均增长速率为14.77 m³/(s·a),并于2001年发生显著突变。(2)汛期降水量和不透水面率是年最大日径流变化的关键驱动因素,最优模型显示前者贡献率超过了70%,表明了降水改变的决定性作用,而不透水面率贡献率超过20%则表明了下垫面的改变对年最大日径流演变存在显著影响。(3)不透水面的增加对年最大日径流和汛期降水量响应关系的影响程度从突变前的6.7%增加到突变后的10.4%,快速城市化已显著改变了流域降水-径流响应过程。研究表明,随着城市发展秦淮河流域的年最大日径流受到人类活动显著影响,洪涝威胁日趋增大,研究结果可为城市化地区防洪减灾提供一定参考。

The evolution of annual maximum daily runoff and its influencing factors under the background of urbanization: An example of Qinhuai River Basin in the lower reaches of the Yangtze River

With the intensification of climate change and human activities, the hydrological process in urbanized areas has been greatly affected, the frequency of extreme hydrological events has increased significantly, and the flood disaster has become more and more serious. It is of great significance to explore the role of flood evolution and quantitative driving factors in urbanized areas for urban flood control. Taking the Qinhuai River Basin, a rapidly urbanized area in the lower reaches of the Yangtze River, as an example, this paper analyzed the evolution characteristics of its annual maximum daily runoff from 1987 to 2018, used multiple linear regression method and generalized additive model GAMLSS to identify the impact of potential driving factors on the evolution of annual maximum daily runoff, and quantifies the factors'' contribution. The results showed that: (1) Under the background of urbanization, the annual maximum daily runoff of Qinhuai River Basin showed a significant upward trend from 1987 to 2018, with an average growth rate of 14.77 m³/(s·a) and a significant mutation occurred in 2001. (2) the optimal model showed that precipitation in flood season and impervious surface ratio are the key driving factors of annual maximum daily runoff change. The former contributed more than 70%, indicating the decisive role of precipitation change; The contribution rate of impervious surface ratio exceeded 20%, also indicated that the change of underlying surface had a significant impact on the evolution of annual maximum daily runoff. (3) The impact of the rise of impervious surface ratio on the relationship between annual maximum daily runoff and flood season precipitation had increased from 6.7% pre-shift to 10.4% post-shift. Rapid urbanization had significantly changed the relationship between runoff and precipitation in this region. Flood control and disaster prevention will be an important task. This study showed that the evolution of annual maximum daily runoff in the Qinhuai River basin was greatly affected by human activities with urbanization and then the flood risk had increased. The research results can provide some reference for flood control and disaster reduction in urbanized areas.