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

Abstract

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

Updating the assessment of climate change impact on temperature at decadal scale and consolidating with CMIP6 future projections

“…Most deficiencies arise due to either the scarcity of data in the past, which impacts the model estimations over time [17], and due to altitude differences when comparing ERA5 grid points with observations in areas with sharp orography or complex terrain [16,[18][19][20]. From a seasonal perspective, ERA5 tends to underestimate summer temperatures and overestimate winter temperatures [17,21,22], resulting in a smaller number of identified heatwaves and a larger number of identified coldwaves [23].…”