| 21 Jan 2025
Understanding Changes in Iceland’s Streamflow Dynamics in Response to Climate Change
Abstract. The hydrological cycle in high-latitude regions is undergoing significant changes due to climate change. Iceland, with its extensive data from undisturbed catchments, provides a unique opportunity to study these changes in snow- and glacier-melt dominated regions. The country's heavy reliance on hydropower, without any connections to other electricity markets, makes understanding these changes crucial. Recent decades have seen warming outpace global warming trends in Iceland, along with increased precipitation, reduced glacier mass, rising soil temperatures and expanded vegetation cover. The impacts of these environmental shifts on streamflow remain largely unexplored. Our study uses the LamaH-Ice dataset, which includes streamflow observations, atmospheric forcings from climate reanalyses, and catchment characteristics, to investigate changes in Iceland's streamflow dynamics over recent decades. We first examine the long-term variability in streamflow and its primary drivers, correlating it with major climate indices. We then analyze trends during the last 30 and 50 years in annual, seasonal, and daily streamflow volumes, the timing of the spring freshet, and extreme flow conditions, linking these changes to environmental conditions and catchment attributes. Results show high inter-annual variability, decadal fluctuations, and strong correlations with the Arctic Oscillation, as reported in earlier studies. Streamflow trends vary by location and river type, with increased precipitation driving higher annual average flows in most rivers, while summer flows have decreased in most rivers, which is linked to lower summer precipitation and increased evapotranspiration. This study is the first to report coherent regional and seasonal trends in Icelandic streamflow. Annual low flows have increased in most rivers. Glacial rivers show positive streamflow trends during the last 50 years, but negative trends during the last 30 years. The findings offer crucial insights into Iceland's hydrological changes amid rapid climatic shifts, with broader implications for reservoir operations and water resources management. This study enhances our understanding of Icelandic hydrology and contributes to global knowledge on climate-induced hydrological changes.
Manuscript Review: "Understanding Changes in Iceland’s Streamflow Dynamics in Response to Climate Change"
1) Impact
This study makes a significant contribution to our understanding of how climate change affects Icelandic streamflow dynamics. By utilizing the extensive LamaH-Ice dataset, the authors provide valuable insights into long-term hydrological trends in Iceland. The findings have important implications for hydropower management, water resource planning, and ecological sustainability. Moreover, the regional focus on Iceland enriches the global discussion on climate-induced hydrological changes.
2) Strengths
3) Weaknesses
4) Specific Editorial Suggestions
Line 80 "it’s location" "its location" (remove the apostrophe)
Line 115 "which only returns as runoff up to decades later": Consider rewording for clarity: "which contributes to runoff decades later"
Line 199 "The warming appears to have slowed in recent years.": Consider adding a reference or supporting data for this claim
Line 390 "An overlying dashed black line indicates that the trend is significant (p < 0.05)." Consider rewording to match the style of other trend significance descriptions
Line 414 "We see that the trend is negative in most cases, although there are only 4 significant trends.": Suggest quantifying "most cases"
Line 505 "While a large majority of annual trends are positive...": Consider rewording for clarity: e.g. "Although most annual trends are positive, only eight out of 25 stations show statistically significant increases for 1973-2023."
Final Recommendations
Highlighting quantitative results in the conclusions would strengthen the paper's data-driven arguments and improve its relevance for climate impact assessments and policy formulation.