INTENSE RAINFALL EVENTS YIELD ENVIRONMENTAL AND HUMAN HEALTH RISKS: A VIEW FROM COASTAL MAINE

Along with a lengthening growing season and increased temperature extremes, coastal Maine can expect more frequent intense rainfall events (>2”/day) due to climate change. In recent years, many such events have impacted Mount Desert Island, ME, home to Acadia National Park. The 108 mi² island hosts millions of visitors annually, contributing to the local economy and increasing demands on natural and built resources. While much attention is given to impacts of large-scale events such as hurricanes, more frequent small-scale events cause chronic damage to infrastructure and threaten environmental and human health. During 2020-2022, college students collaborated with local researchers and resource managers to document impacts of intense rainfall events on the island’s post-glacial landscapes, watersheds, and drinking water. Intense rainfall (~5” in 3hr) focused on the northern bedrock slopes of the mountains of Acadia resulted in high runoff rates and stream discharge that overwhelmed culverts, caused erosion of the historic “Carriage Roads,” and led to sedimentation in the park’s forests, streams, and wetlands. A similar event (~2” in 1hr) triggered the catastrophic draining of an upland lake due to beaver dam failure, causing a debris flow that incised a ~6’ deep channel in the forest floor and buried a popular trail in ~2m of material. Fortunately, nobody was injured as the event occurred in the early morning hours. Rain during the dry summer months recharge water resources, which is important considering the elevated water demands due to seasonal visitors and as >50% of residents rely on private wells for their drinking water. However, changing groundwater levels and flow conditions can influence groundwater chemistry. Pre- and post-storm testing of private well water revealed temporarily elevated contaminant abundances to levels above state standards after rain events. Thus, testing private wells every 1-5 years as state guidelines suggest, may not be often enough to reveal exposure to contaminants associated with negative health outcomes. With more frequent intense rain events forecasted for many regions, we suggest that identification and documentation of associated hazards will enable the mitigation and planning needed to reduce environmental and human health risks and build resilient communities.