The potential for widespread landslides is generally increased when extraordinary wet periods occur during times of elevated subsurface hydrologic conditions. A series of storms in early 2018 in Pittsburgh, Pennsylvania, overlapped with a period of increased shallow soil moisture and rising bedrock groundwater levels resulting from seasonally diminished evapotranspiration and induced widespread landslides in the region. Most of the landslides were shallow slope failures in colluvium, landslide deposits, and/or fill. However, deep-seated landslide activity also occurred and corresponded with record cumulative precipitation from late February to April and bedrock groundwater levels rising to an annual high. Landslides blocked or damaged roads, adversely affected multiple houses, disrupted electrical service, crushed vehicles, and resulted in considerable economic losses. The initial landslides occurred during or immediately after a rare period of three successive days of heavy rain that began on February 14. Subsequent landslides between late February and April were induced by multiday storms with smaller rainfall totals. As shallow soil moisture at a monitoring site rose above a volumetric water content of 32%, the mean rainfall intensities necessary to induce slope failure in colluvium and other surficial deposits decreased. Deep-seated landslide movement occurred in the region mostly when the groundwater level in a bedrock observation well was shallower than 1.7 m. The availability of hydrologic and landslide movement monitoring data during this extraordinary series of storms highlighted the evolution of the landslide hazard with changing moisture conditions and yielded insights into potential hydrologic criteria for anticipating future widespread landslides in the region.

当地下水文条件升高时，如果出现异常潮湿的时期，通常会增加发生广泛滑坡的可能性。宾夕法尼亚州匹兹堡在2018年初发生了一系列暴风雨，同时由于蒸发蒸腾量的季节性减少和该地区的广泛滑坡而导致浅层土壤水分增加和基岩地下水位上升的时期重叠。大多数滑坡是在崩积层，滑坡沉积物和/或填土中的浅层边坡破坏。但是，也发生了深层滑坡活动，这与2月下旬至4月的创纪录累积降水和基岩地下水位上升到年度最高水平相对应。滑坡阻塞或损坏道路，对多栋房屋造成不利影响，电力服务中断，车辆被压碎，并造成了可观的经济损失。最初的滑坡发生在2月14日开始的连续三天的罕见罕见降雨期间或紧随其后的罕见时期。随后的2月下旬至4月之间的滑坡是由降雨总量较小的多日风暴引起的。随着监测地点的浅层土壤湿度上升到超过32％的体积水分含量，诱发崩塌和其他表层沉积物的边坡破坏所必需的平均降雨强度下降。当基岩观测井的地下水位低于1.7 m时，该地区发生了深层滑坡运动。