Hillslope-stream connectivity significantly affects streamflow and water quality responses during rainfall and snowmelt events, but is difficult to quantify. One approach to quantify subsurface hillslope-stream connectivity is graph theory, which considers linear connections between groundwater measurement sites. We quantified subsurface connectivity based on surface topography and shallow groundwater data from four small (<14 ha) headwater catchments in the Italian Dolomites and the Swiss pre-Alps, determined the relation between rainfall, antecedent wetness conditions and subsurface connectivity and assessed the sensitivity of the results to changes in the measurement network. Event total stormflow was correlated to maximum subsurface connectivity. Subsurface connectivity increased during rainfall events but maximum connectivity occurred later than peak streamflow, resulting in anti-clockwise hysteretic relations between the two. Subsurface connectivity was positively correlated to rainfall amount. Maximum subsurface connectivity was related to the sum of total rainfall plus antecedent rainfall for the Dolomitic catchments, but these relations were less clear for the pre-alpine catchments. For the pre-alpine catchments, the fractions of time that the groundwater monitoring sites were connected to the stream were significantly correlated to the upslope site characteristics, such as the Topographic Wetness Index. For the Dolomitic catchments, the fractions of time that the monitoring sites were connected to the stream were correlated to the topographic characteristics of the upslope contributing area for the catchment with the small riparian zone, and with the distance to the nearest stream for the catchment with the large riparian zone. The leave-one-out sensitivity analysis showed that small changes in the structure of the groundwater monitoring networks had a limited influence on the results, suggesting that graph-theory approaches can be used to describe subsurface hydrologic connectivity. However, the proposed graph-theory approach should be verified in other catchments with different groundwater monitoring networks.

在降雨和融雪事件期间，山坡-溪流的连通性会显着影响溪流和水质响应，但难以量化。图论是量化地下山坡-河流连通性的一种方法，它考虑了地下水测量点之间的线性关系。我们根据地貌和来自意大利白云岩和瑞士阿尔卑斯山前四个小型（<14公顷）上游水源地的浅层地下水数据对地下连通性进行了定量分析，确定了降雨，前期湿润条件与地下连通性之间的关系，并评估了结果将导致测量网络的变化。事件总的暴雨流与最大地下连通性相关。在降雨事件期间，地下连通性增加，但最大连通性发生在峰值流量之后，从而导致两者之间出现逆时针磁滞关系。地下连通性与降雨量呈正相关。最大的地下连通性与多洛米奇流域的总降雨加上前期降雨的总和有关，但是对于高山前流域，这些关系还不清楚。对于高山前流域，地下水监测点与河流相连的时间分数与上坡点特征（如地形湿度指数）显着相关。对于多洛米特流域，监测点与河流相连的时间分数与小河岸带集水区的上坡贡献区的地形特征以及大河岸带集水区到最近溪流的距离相关。留一法敏感性分析表明，地下水监测网络结构的细微变化对结果的影响有限，表明图论方法可用于描述地下水文连通性。但是，建议的图论方法应在具有不同地下水监测网络的其他流域进行验证。留一法敏感性分析表明，地下水监测网络结构的细微变化对结果的影响有限，表明图论方法可用于描述地下水文连通性。但是，建议的图论方法应在具有不同地下水监测网络的其他流域进行验证。留一法敏感性分析表明，地下水监测网络结构的细微变化对结果的影响有限，表明图论方法可用于描述地下水文连通性。但是，建议的图论方法应在具有不同地下水监测网络的其他流域进行验证。