Can peatland restoration enhance drought and flood resilience in boreal forests?

Peatlands, unique wetlands where peat forms because waterlogging inhibits decomposing organisms, are predominantly found in the boreal region. In Sweden, nearly 18% of the land surface is covered by forested peatlands.  However, many of these areas have experienced severe anthropogenic disturbances in the 20^th century. Drainage, a common practice to improve soil conditions for agriculture and forestry, along with commercial peat harvesting, has exerted considerable pressure on these ecosystems. In recent years, peatlands have been recognized for their value in climate-change mitigation, serving as crucial ecosystems that can store carbon and water. Peatland restoration, often referred to as rewetting, is considered an effective nature-based solution to reinstate hydrological, ecological, and biogeochemical conditions essential for various ecosystem services. Global and national policies actively promote peatland restoration, positioning it as a highly effective measure to build resilience against climate-change impacts. Following a series of extreme summers in Sweden, especially the mitigation of hydroclimatic extreme events, such as floods and droughts, is a widely claimed benefit. However, assessing the success of restoration efforts is difficult due to diverse hydroclimatic conditions, a wide range of catchment properties, long response times to restoration measures, and a limited number of long-term monitored restoration case studies. Specifically, restoration impacts on hydrological functioning, including water storage, flood control, groundwater recharge, and drought buffering, remain poorly understood. To strengthen the scientific basis and provide comprehensive insights for decision-makers, we conducted a literature review synthesizing existing empirical evidence on how rewetting boreal peatlands influences hydrological feedbacks. Our focus was particularly on the role of peatlands during drought and flood events, how their location and the time elapsed after restoration affects drought and flood vulnerability, and how peatlands themselves might be impacted by such extreme events. Our results represent a crucial initial step towards understanding the hydrological mechanisms regulating peatlands over time and under various hydroclimatic conditions, which is pivotal in guiding future conservation, rewetting and sustainable use of peatlands as nature-based solutions.