Impact of wildfires on the drinking water catchment for the capital area of Iceland – a case study†

Abstract

Climate change is leading to an increase in extreme weather events in the Arctic, which can significantly affect both the quality and availability of drinking water. Prolonged droughts lower groundwater levels and reduce soil moisture that elevates the risk of wildfires, which can contaminate water resources and damage water supply infrastructure. This case study examines the impact of wildfires on water quality in porous volcanic strata in the Arctic. The primary water extraction area for the capital region of Iceland supplies drinking water to six municipalities, representing approximately 64% of the country's population. The water source is mainly located in a postglacial porous lava field with thin volcanic strata and limited surface water. On May 4th, 2021, a large wildfire occurred in the watershed following a prolonged drought, burning 56.5 hectares of land. Three of the water intake zones for the capital region are situated 300 meters to a few kilometres from the fire-affected area. Water quality monitoring data from these zones, covering the period 2011–2023 and comprising 47 samples (28 pre-fire and 19 post-fire), were analysed. The results show the presence of polycyclic aromatic hydrocarbons (PAHs) and volatile organic compounds (VOCs), as well as an increase in certain metals after the wildfire. The total concentration of the five detected PAHs ranged from 1.1 to 7.3 ng l⁻¹, with PAHs detected up to five months post-wildfire. These were predominantly five- or six-ring carcinogenic PAHs, though levels remained well below the parametric values set by Icelandic drinking water regulations. Some VOCs were also detected after the wildfire, albeit mostly at a later stage. Additionally, several metals were found in concentrations up to nearly six times higher than the median values recorded from 2011 to 2020. These findings suggest that groundwater quality is vulnerable to contamination following wildfires, underscoring a critical knowledge gap regarding the impacts of climate change on the water sector and the need for enhanced risk mitigation strategies.