Abstract

Increasing air temperatures reduce the duration of ice cover on lakes and rivers, altering their water quality, ecology, biodiversity, and physical, economical and recreational function. Using a unique in-situ record of freeze and breakup dates, including records dating back to the beginning of the 18th century, we analyze changes in ice duration (i.e., first freeze to last breakup), freeze and breakup patterns across Sweden. Results indicate a significant trend in shorter ice duration (62 %), later freeze (36 %) and earlier breakup (58 %) dates from 1913–2014. In the latter 3 decades, the mean observed ice durations have decreased by about 11 days in northern (above 60N) and 28 days in southern Sweden, whereas the average freeze date occurred about 10 days later and breakup date about 17 days earlier in southern Sweden. The rate of change is roughly twice as large in southern Sweden as in its northern part. Sweden has experienced an increase in occurrence of years with an extremely short ice cover duration (i.e., less than 50 days), which occurred about eight times more often in southern Sweden than previously observed. Our analysis indicates that even a 1 °C increase in air temperatures in southern (northern) Sweden results in a mean decrease of ice duration of 22.5 (7.6) days. Given that warming is expected to continue across Sweden during the 21st century, we expect increasingly significant impacts on ice cover duration and hence, ecology, water quality, transportation, and recreational activities in the region.

Highlights

  • The world’s freshwater systems are critically important for all humans and they have experienced significant environmental changes due to human activities and anthropogenic climate change (Dudgeon et al 2006) (Vörösmarty et al 2010)

  • Increasing air temperatures reduce the duration of ice cover on lakes and rivers, altering their water quality, ecology, biodiversity, and physical, economical and recreational function

  • Since a long time series of lake ice observations can serve as a proxy for climate change and provide a convenient climate index (Duguay et al 2003), we extend these previous studies using more recent observations, longer records of ice duration, breakup, and freeze data, and more observation sites across the whole of 65 Sweden

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Summary

Introduction

The world’s freshwater systems are critically important for all humans and they have experienced significant environmental changes due to human activities and anthropogenic climate change (Dudgeon et al 2006) (Vörösmarty et al 2010). One impact of global warming is the reduction in ice cover duration of freshwater systems, often associated with both a later freeze and an earlier breakup (Duguay et al 2003). Decreased ice cover duration and earlier ice breakup have critical ecological consequences, influencing the timing of photosynthesis (Quayle et al 2002) (Leppäranta et al 2012), productivity and biodiversity of 40 phytoplankton, and the occurrence of fish kill (Leppäranta et al 2003), (Watz et al 2016), as well as shaping the vegetation of flowing waters (Lind et al 2014). Changes in ice duration modulate the energy and moisture exchange over the water surface (Duguay et al 2003) and the timing of vertical mixing and stratification in lakes (Bengtsson 2011)

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