在快速城市化的大背景下,城市地区下垫面变化是影响径流过程的重要因素,而影响机制尚待研究。选择武汉市青山区作为典型研究区域,通过遥感技术、GIS分析以及BP神经网络模型等方法,对典型研究时段城市下垫面变化进行了定量评估,并分析了这些变化对径流系数的影响。通过对比分析发现:城市下垫面变化对径流系数具有显著影响,随着建筑用地和道路的增加,径流系数呈现上升趋势,2009—2017年研究区径流系数从0.399增至0.535;而绿地、植被等用地面积的增加则有助于降低径流系数,同时海绵城市建设通过增加强透水地面面积,额外增加雨水调蓄容积,可达到降低径流系数的作用,海绵城市项目实施后,2017年径流系数为0.535,较海绵城市项目实施前降低0.051。研究成果可为城市规划和防洪排涝系统的设计提供科学依据,也可为城市水文循环和水资源管理提供技术支撑。

[Objective] Against the background of rapid urbanization, changes in the urban underlying surface constitute a significant factor influencing runoff processes, yet their mechanisms remain inadequately studied. [Methods] Taking Qingshan District of Wuhan City as a representative study area, this paper used remote sensing technology, GIS analysis, and a BP neural network model to quantitatively assess urban underlying surface changes during the typical study period and analyze its impact on the runoff coefficient. [Results] (1) Under urban development, land use in the study area from 2002 to 2017 shifted overall from permeable to impermeable surfaces. Vegetation, rooftops, and other land-use types fluctuated, whereas water bodies shrank year by year. Construction of the sponge city demonstration zone in 2015 slowed this trend. (2) The runoff coefficient was jointly affected by underlying surface changes and rainfall. However, urban rainfall changed little over short timescales, the impervious surface ratio was the dominant factor. As the area ratio of high-runoff land use (e.g., hardened ground) increased and that of low-runoff land use (e.g., vegetation, green space) decreased, the runoff coefficient rose yearly—from 0.399 in 2009 to 0.535 in 2017—showing that land-use change directly altered the runoff coefficient to some extent. (3) After sponge city interventions, the annual runoff coefficient showed a decreasing trend; in 2017 it was 0.535, 0.051 lower than in 2014. [Conclusions] Sponge city construction reduces the runoff coefficient by expanding highly permeable surfaces and adding storage volume, thereby mitigating the adverse impacts of urban development on stormwater regulation capacity. The study offers scientific guidance for urban planning and flood-control drainage system design, and technical support for urban hydrological cycles and water-resource management.