Near‐surface mean wind in Switzerland: Climatology, climate model evaluation and future scenarios

Graf, M.; Scherrer, Simon C.; Schwierz, Cornelia; Begert, Michael; Martius, Olivia; Raible, Christoph C.; Brönnimann, Stefan

doi:10.1002/joc.6108

Cited by 12 publications

(5 citation statements)

References 44 publications

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“…The intensity and duration of autumn mixing affect the dissolved oxygen concentration at ice‐on (Kirillin et al, 2012; Leppäranta, 2015). Like most inner Alpine valleys (Graf et al, 2018), Lake Tovel has little wind (Eccel & Toller, 2006), especially during late autumn (mean wind velocities < 0.5 m s −1 ). By mid‐November, Lake Tovel was usually isothermal or showed only weak thermal stratification as indicated by density‐based mixing indices.…”

Section: Discussionmentioning

confidence: 99%

Ice Cover and Extreme Events Determine Dissolved Oxygen in a Placid Mountain Lake

Flaim

Andreis

Piccolroaz

et al. 2020

Water Resources Research

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A decrease in hypolimnetic dissolved oxygen (DO) is a commonly seen effect of climate change. However, in oligotrophic Lake Tovel (Italy), a deep mountain lake, annual mean DO (% saturation) has increased from near anoxia to >20% in the bottom layer (35-39 m). We analyzed long-term patterns of DO (1937-2019) using different methods (correlation and trend analysis, identification of extreme events) to link DO to drivers and indices of mixing. While spring mixing remained temporally limited, later ice-in (5.1 days decade −1) and the positive relationship between ice-in and DO the following year evidenced autumn mixing as the main driver for hypolimnetic DO increase. Extreme meteorological events also replenished hypolimnetic DO. Using DO and conductivity (1995-2019), we identified 14 deep mixing events with hypolimnetic DO > 40%. Density-based indices (Schmidt stability, relative thermal resistance, Lake Number, and Wedderburn Number) only partially captured these events that were related to snowmelt, flooding, and cold spells during spring and autumn, with a carryover effect sometimes lasting >1 year. Recently, annual mean DO in the upper layer decreased beyond temperature-dependent solubility. This decrease was not comprehensively confirmed by statistical tests but was possibly linked to atmospheric stilling. We suggest that Lake Tovel's shift from meromixis to dimixis was driven by climate warming (i.e., increasing air temperature 0.6°C decade −1) that delayed ice-in and increased autumn mixing. Our work underlines the vulnerability of mountain lakes and their different response to climate change with respect to more studied lowland lakes. Plain Language Summary Dissolved oxygen is fundamental for aquatic life. Lake Tovel (Brenta Dolomites, Italy) has a long history of limnological studies starting in the 1930s; therefore, we can study oxygen's long-term evolution. Contrary to most temperate lakes, dissolved oxygen is increasing in the deep layers of Lake Tovel since the 1990s. We linked this to later ice-in: as a consequence of climate change, Lake Tovel has lost almost 3 weeks of ice cover since the mid-1980s. This loss (5.1 days decade −1) in ice-in is much steeper than in lowland lakes. Because dissolved oxygen is replenished in lakes by mixing, a longer ice-free period means more time to mix, with oxygen reaching deeper layers. Extreme events such as heavy snowmelt, flooding, and cold spells during spring and autumn also increased mixing with effects often lasting over a year. However, in the last decade, we are beginning to see a decrease in dissolved oxygen at the surface, probably because of less wind. Years with little snow also tend to coincide with lower concentrations of dissolved oxygen in the deep layers. Changes in air temperatures, precipitation, and wind will determine the evolution of dissolved oxygen in Lake Tovel, a sentinel mid-altitude lake for climate change.

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Section: Discussionmentioning

confidence: 99%

Ice Cover and Extreme Events Determine Dissolved Oxygen in a Placid Mountain Lake

Flaim

Andreis

Piccolroaz

et al. 2020

Water Resources Research

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“…It can be seen that the Alpine region (AL, purple color) presents the lowest mean values, with an overall ERA5 underestimation, together with the larger overestimated cut-in and light wind hours. This result is related to the difficulties for modelled wind to accurately describe the atmospheric dynamics over these mountainous areas [8,17,71,72]. To reduce such biased results could be obtained using higher resolution modelling simulations [19].…”

Section: Comparison Between Low Wind Conditions From Era5 and Observa...mentioning

confidence: 99%

“…Europe is a challenging region for wind studies, due to the presence of numerous areas of complex orography. Several studies [3,[9][10][11][12][13] have analysed the basic wind speed statistics and have shown the importance of the spatial and temporal resolution of climate models for wind modelling, as can be seen in the analysis of coastal winds [14,15], or areas with orographic complexity [8,[16][17][18][19].…”

Section: Introductionmentioning

confidence: 99%

Low wind climatology (1979-2018) over Europe from ERA5 reanalysis

Gutiérrez

Molina

Ortega

et al. 2023

Preprint

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Research and wind speed assessment has increased lately among other things, due to its interest as a renewable energy resource. Whereas mean values and trends are commonly studied, less attentions is paid to the evaluation of extremes. In terms of lower winds, it is difficult to find agreement on a definition for those conditions. Here, the long-term characterization of low wind values over oceanic and land regions in Europe is assessed from hourly data of ERA5 reanalysis for the period 1979-2018. An absolute threshold (cut-in) related to a generalized wind power curve is used. The number of hours below cut-in threshold (3 m/s) present a reasonable agreement with the available observations, with annual values around 3000-4000 h for most of the locations over Europe, although severe limitations are found to properly represent wind speed field over mountainous areas. Important differences in the amount of hours below cut-in threshold are obtained between northern and southern regions of the domain, where the overall more complex orography and coast line seems to play a relevant role. Interannual and seasonal low wind variability show differences larger than 20-25\% for both timescales. Atlantic Ocean and Mediterranean regions behave differently, but both with less low wind values than land regions. In terms of persistence, analysis of low wind spells indicate that the largest ones, on annual averages, can reach up to 120 consecutive hours (4-5 days) over many land areas. Overall, mean hourly wind spells range from 10 to 20 h, with more than 200 episodes per year

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“…Over recent years a number of compound extremes have been investigated. For instance, several studies have analysed the dependence between storm surge and heavy precipitation (Wahl et al, 2015;Zheng et al, 2013;Bevacqua et al, 2019) or extreme runoff (Ward et al, 2018;Hendry et al, 2019) to estimate the risk of compound flooding in coastal areas. Compound droughts and heatwaves have been studied for dif-ferent regions and varying temporal scales (Mazdiyasni and AghaKouchak, 2015;Zscheischler and Seneviratne, 2017;Manning et al, 2019;Sutanto et al, 2020;Zscheischler and Fischer, 2020).…”

Section: Introductionmentioning

confidence: 99%

Evaluating the dependence structure of compound precipitation and wind speed extremes

et al. 2021

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Abstract. Estimating the likelihood of compound climate extremes such as concurrent drought and heatwaves or compound precipitation and wind speed extremes is important for assessing climate risks. Typically, simulations from climate models are used to assess future risks, but it is largely unknown how well the current generation of models represents compound extremes. Here, we introduce a new metric that measures whether the tails of bivariate distributions show a similar dependence structure across different datasets. We analyse compound precipitation and wind extremes in reanalysis data and different high-resolution simulations for central Europe. A state-of-the-art reanalysis dataset (ERA5) is compared to simulations with a weather model (Weather Research and Forecasting – WRF) either driven by observation-based boundary conditions or a global circulation model (Community Earth System Model – CESM) under present-day and future conditions with strong greenhouse gas forcing (Representative Concentration Pathway 8.5 – RCP8.5). Over the historical period, the high-resolution WRF simulations capture precipitation and wind extremes as well as their response to orographic effects more realistically than ERA5. Thus, WRF simulations driven by observation-based boundary conditions are used as a benchmark for evaluating the dependence structure of wind and precipitation extremes. Overall, boundary conditions in WRF appear to be the key factor in explaining differences in the dependence behaviour between strong wind and heavy precipitation between simulations. In comparison, external forcings (RCP8.5) are of second order. Our approach offers new methodological tools to evaluate climate model simulations with respect to compound extremes.

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Near‐surface mean wind in Switzerland: Climatology, climate model evaluation and future scenarios

Cited by 12 publications

References 44 publications

Ice Cover and Extreme Events Determine Dissolved Oxygen in a Placid Mountain Lake

Ice Cover and Extreme Events Determine Dissolved Oxygen in a Placid Mountain Lake

Low wind climatology (1979-2018) over Europe from ERA5 reanalysis

Evaluating the dependence structure of compound precipitation and wind speed extremes

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