Browsing by Subject "peatland hydrology"

Aapa mires are northern peatlands of high conservation value that are currently threatened by hydrological changes caused by land use and climate change. In pristine hydrological state they are characterized by wet fens and waterflows from surrounding landscape, particularly during the snow melt time in spring. In future climate conditions, increased summer evapotranspiration and earlier spring floods can possibly reduce summertime water availability in aapa mires. It is however unclear, how strong effect the changes in the different climatic hydrological components exactly have on aapa mire wetness on regional level. Particularly spatial information of climatic sensitivity of mires is lacking. Current knowledge and large-scale hydrological predictions are based mainly on measurements at individual sites, modeling and generalization, even though climate-wetness relationships seem to vary largely from site to site. In this study, Sentinel-2 satellite imagery from 2017-2020 was used to produce regionally representative information of interannual summer wetness variability in Finnish aapa mires, and to quantify with statistical modeling the relationships to interannual climatic variation based on the observations. Monthly values for optical metrics of surface moisture and areal extent of the wettest mire surfaces were extracted for wet fen mires of the Natura 2000 conservation network (n=2201), covering the whole aapa mire zone of Finland. Wetness metrics from June and July in a regionally representative sample (n=400) of mires were linked to the respective yearly climatic data of summer-time water balance (WAB, precipitation - evaporation), day of snowmelt and snow water equivalent maximum. Climate-wetness relationships were estimated regionally for the eight aapa mire zone sub-regions with mixed effects models. The resulting satellite-derived metrics revealed high interannual variability of the surface moisture conditions and the areal extent of wet surfaces in aapa mires, and this variability was shown to be significantly connected to variation in the climatic variables. Regional variation in climatic sensitivity was remarkable. Mires in the most sensitive regions had twice as strong responses to varying WAB conditions and drought-periods than mires in the least sensitive regions. If the short-term responses are assumed to reflect the sensitivity to climatic changes in the long-term, these effects imply that aapa mires might experience remarkable hydrological changes in the future, especially in the most sensitive areas in the southern and the western parts of the Finnish aapa mire zone. The results emphasize the important role of yearly snow conditions alongside summertime WAB as a driver of aapa mire wetness, especially in June but also later in the summer.