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Towards improved understanding of the worldwide decline of wind speed in a climate change scenario

Periodic Reporting for period 1 - STILLING (Towards improved understanding of the worldwide decline of wind speed in a climate change scenario)

Reporting period: 2016-09-01 to 2018-08-31

Wind speed has declined over mid-latitude regions over the past 50-years, a phenomenon known as “stilling”. Scientists have paid little attention on the study of the causes behind wind changes, and are divided to how global warming is impacting wind speed changes. The identification of the exact cause(s) is still unresolved and, therefore, the overall objective of this action was to better understand the current slowdown of winds in a changing climate by filling the key gap of short availability (since the 1960s) and low quality of instrumental records. Improving our knowledge on wind speed changes is of great scientific, socioeconomic, and environmental interest to advance climate change adaptation. For instance, the “stilling” phenomenon impacts a wide array of spheres, including: (i) wind power generation; (ii) agriculture, forestry, and hydrology due to evapotranspiration; (iii) air quality and impacts on human health and environment; (iv) wind damage propagation in forest; and (v) migration of wind-dispersed plant species, among others. The STILLING project addressed one of the major constraints to assess wind speed variability with high confidence: i.e. the quantity and the quality of wind speed observations to allow a reliable study. This action rescued, quality-controlled and homogenized historical wind speed data for long-term time-scales never explored before (prior to the 1960s), and improved our understanding of wind speed changes in the past. These kind of investigations that look at past wind speed changes are crucial to better assess future wind speed projections. The results of this MSCA action have shown new evidences on e.g. the impact of the degradation of anemometers on wind speed measurements; the climate variability of winds and the influence of atmospheric circulation for a hot-spot region such as the Canary Islands (Eastern North Atlantic region) since the 1940s; and the wind speed changes worldwide during last decades. The STILLING project has consolidated a novel research line on the study of wind changes, and has raised new research questions to be investigated in the future: are extreme wind gusts also declining in line with the “stilling” for mean wind or more frequent and severe wind gusts are occurring due to a changing climate?.
The STILLING project has improved our knowledge on the wind speed changes over spatio-temporal scales which have not been explored before. The work carried out by scientists from the University of Gothenburg and the partner organization at the Royal Netherlands Meteorological Institute consisted on a innovative strategy towards: (i) compilation of historical wind records from different climate databases and old-weather books; (ii) creation of new statistical algorithms/software to quality control and homogenize raw wind records; and (iii) analysis of wind speed variability over time-windows (prior to the 1960s) and regions never assessed in the scientific literature. Firstly, the project was based on the compilation of wind speed series from various data sources and throughout National Weather Services (NWS) around the world. In collaboration with staff of NWS, we also developed templates to rescue and digitize wind records from old weather books. Secondly, we designed a pioneering approach to homogenize wind records, and implemented it in the Climatol software, representing a significant outcome of this MSCA action. Thirdly, and finally, this work produced the first homogenized wind dataset with records prior to the 1960s (~3,500 stations; some of them covering a centennial time-scale), which has helped to assess and attribute wind speed variability for different regions across the world. As planned, project results have already been disseminated in peer-reviewed international scientific journals (open access) such as Climate Dynamics, International Journal of Climatology, Atmospheric Research, and the Bulletin of the American Meteorological Society, and presented in key conferences as those organized by the European Meteorological Society or the European Geophysical Union. Press releases about the STILLING project in e.g. the Horizon Magazine, Cosmos Magazine or De Standaard newspaper helped to disseminate our research beyond the academia. The homogenized databases and results achieved during the STILLING project are expected to extend wind studies to more complete analyses, which will undoubtedly help to unravel the drivers behind the “stilling” phenomenon in a changing climate.
The STILLING project represented the first attempt to rescue, homogenize and assess wind speed datasets over spatio-temporal scales never explored before in the scientific literature, with the ultimate goal to better understand the current “stilling” phenomenon. In particular, this MSCA action has developed the first long-term and quality-controlled/homogenized wind speed dataset to study wind speed variability prior to the 1960s until today. In particular, the homogenization approach defined in this research project represents a significant outcome of this MSCA IF with respect to the state-of-the-art, as it automatically homogenizes a large number of wind speed series, uses the closest reference series even not sharing a common period with candidate series or presenting missing data, and fills in all the missing data. The assessment and attribution of wind speed changes and the results on this project have direct impacts on different socioeconomic and environmental areas. For instance, our results published and new databases developed will affect policy-makers evaluating the influence of a future weakening of wind speed on power generation (wind industry), or advancing climate change adaption because of the impact of wind speed on evaporation (i.e. droughts and water resources), among many other areas. Lastly, the STILLING project also had impact on the scientific career of the MSCA fellow by being awarded with two highly prestigious grants (tenure-track positions) as principal investigator at the interface of Climatology and Meteorology in Europe.