Intensification of the water cycle in northern catchments: Long-term isotopic and hydrometric evidence and consequences

Water limitation has become one of the most pressing threats to groundwater and forest resources also in the north. Despite increased precipitation in many high latitude regions, suggested by both empirical observations and climate models, large regions are on a trajectory of increasing water limitation that already caused substantial loss of forest biomass, threatening targets for biodiversity, carbon sequestration, and bioeconomy. Key to these northern challenges are how the intensification of the water cycle results in earlier snowmelt, enhanced evapotranspiration (ET) rates, lower groundwater levels during the vegetation period and declining summer runoff. In my talk, I will present 25 years of consistent water isotopic data from precipitation, groundwater and stream flow in order to disentangle critical processes that determine the availability of water for trees and streams during the growing season. I will draw my examples from the Krycklan Catchment Study (KCS) that has supported water isotope research for over tree decades. The research infrastructure is based on a 6790 ha catchment and includes a dozen gauged streams, 150 groundwater wells, 500 permanent forest inventory plots, a large radar system for tree water content measurements and a 150 meter tall tower for biosphere-atmosphere carbon and water exchange processes. The combination of long-term monitoring, shorter-term research projects, and large-scale experiments, including manipulations of the water cycle related to climate, forest management and peatland restoration. This work has contributed to our process understanding of water in the boreal landscape, while also supporting the development of better models and guidelines for research, policy, and management.