Trends of daily peak wind gusts in Spain and Portugal, 1961–2014

Abstract

Given the inconsistencies of wind gust trends under the widespread decline in near-surface wind speed (stilling), our study aimed to assess trends of observed daily peak wind gusts (DPWG) across Spain and Portugal for 1961-2014 by analyzing trends of (i) the frequency (90th percentile) and (ii) the magnitude (wind speed maxima) of DPWG. Wind gust series were homogenized on a daily basis, using MM5-simulated series as reference, resulting in 80 suitable station-based data sets. The average DPWG 90th percentile frequency declined by À1.49 d decade À1 (p < 0.05) annually. This showed marked seasonal differences: decreasing in winter (À0.75 d decade À1 ; p < 0.05) and increasing in summer (+0.18 d decade À1 ; p > 0.10). A negligible trend was calculated for the annual magnitude of DPWG (À0.005 m s À1 decade À1 ; p > 0.10), with distinct seasonality: declining in winter (À0.168 m s À1 decade À1 ; p < 0.10) and increasing in summer (+0.130 m s À1 decade À1 ; p < 0.05). Combined, these results reveal less frequent and declining DPWG during the cold semester (November-April) and more frequent and increasing DPWG during the warm semester (May-October). Large-scale atmospheric changes such as the North Atlantic Oscillation Index (negative correlations~À0.4-À0.6; p < 0.05) and the Jenkinson and Collison scheme (positive correlations mainly with Westerly regime:~+0.5-0.6; p < 0.05) partly account for the decadal fluctuations of both frequency and magnitude of DPWG, particularly in winter. However, the North Atlantic Oscillation index-DPWG relationships are smaller in spring, summer, and autumn (~À0.1-À0.2; p > 0.10), especially for the frequency, suggesting the role of local-to-mesoscale drivers.In view of (i) the minimal number of studies reporting long-term changes from observed DPWG over land; (ii) the overall inconclusive nature DPWG trends observed from anemometers; and (iii) the substantial societal and environmental impact of this natural hazard (e.g., for human safety, maritime and aviation activities, engineering and insurance applications, and energy production), additional trend assessments, and studies that assess these trends from a large-scale atmospheric circulation perspective are needed to increase our understanding of wind extremes [Vose et al., 2014]. The principal objective of this study is to determine, for AZORIN-MOLINA ET AL.

Recent trends in wind speed across Saudi Arabia, 1978–2013: a break in the stilling

“…These data uncertainty are due to climate monitoring issues such as instrumental malfunctions, anemometer changes and technological improvements, shifts in measurement height and sites and so on (Pryor et al, ), and the absence of metadata to accurately detect break‐points (Li et al, ). Recently, some advances on the homogenization of such non‐climatic changes in wind speed series have been achieved by the scientific community (Wan et al, ; Azorin‐Molina et al, , ), allowing one to make accurate wind speed trend assessments from quality‐controlled and homogenized data sets as for SA.…”

“…() evoked the term ‘stilling’ to refer to this declining trend. Two major drivers of stilling have been proposed: (1) an upward trend in land‐surface roughness (Vautard et al, ; Bichet et al, ; Wever, ); and (2) decadal variability of atmospheric circulation (Lu et al, ; Azorin‐Molina et al, , ). This phenomenon is also found to be in line with the widespread reduction in pan evaporation, which has been attributed to stilling (e.g.…”

Tendencias de las rachas máximas diarias de velocidad del viento en España y Portugal, 1961-2014

“…En total se ajustaron 85 discontinuidades, y el total de las 80 series originales (73 España y 7 Portugal) fueron utilizadas para el análisis de tendencias. Una descripción detallada del proceso de homogeneización de series diarias de rachas máximas de velocidad del viento se puede consultar en Azorin-Molina et al (2016).…”

“…Según Azorin-Molina et al (2016), estos cambios en la frecuencia y magnitud de las rachas máximas de velocidad del viento están asociados, principalmente en invierno, a la variabilidad decadal de la Oscilación del Atlántico Norte; sin embargo, se ha comprobado que la circulación atmosférica juega un papel débil en primavera, verano y otoño, lo que sugiere que otros mecanismos a escala local y mesoescalar explicarían las tendencias observadas en los últimos 50-60 años.…”

“…Sin embargo, el estudio de las tendencias de las rachas máximas diarias de la velocidad del viento ha sido escasamente abordado, y sólo en los últimos años ha adquirido un mayor interés debido al posible impacto del cambio climático en la frecuencia e intensidad de los fenómenos meteorológicos extremos: es decir, los temporales de fuerte viento. Recientemente, Azorin-Molina et al (2016; vid "Tabla 1") hicieron una revisión bibliográfica detectando que en un 55% de los estudios científicos se observaba un descenso en las rachas máximas diarias de velocidad del viento, acorde con el fenómeno "stilling"; en cambio, en el 45% restante se observaba un ascenso o no se identificaba una tendencia clara de los episodios de viento extremo.…”