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

We analyse recent trends and variability of observed near-surface wind speed from 19 stations across Saudi Arabia (SA) for 1978-2013. The raw wind speed data set was subject to a robust homogenization protocol, and the stations were then classified under three categories: (1) coast, (2) inland and (3) mountain stations. The results reveal a statistically significant (p<0.05) reduction of wind speed of -0.058m s(-1) dec(-1) at annual scale across SA, with decreases in winter (-0.100m s(-1) dec(-1)) and spring (-0.066m s(-1) dec(-1)) also detected, being non-significant in summer and autumn. The coast, inland and mountain series showed similar magnitude and significance of the declining trends across all SA series, except for summer when a decoupled variability and opposite trends of wind speed between the coast and inland series (significant declines: -0.101m s(-1) dec(-1) and -0.065m s(-1) dec(-1), respectively) and the high-elevation mountain series (significant increase: +0.041m s(-1) dec(-1)) were observed. Even though wind speed declines dominated across much of the country throughout the year, only a small number of stations showed statistically significant negative trends in summer and autumn. Most interestingly, a break in the stilling was observed in the last 12-year (2002-2013) period (+0.057m s(-1) dec(-1); not significant) compared to the significant slowdown detected in the previous 24-year (1978-2001) period (-0.089m s(-1) dec(-1)). This break in the slowdown of winds, even followed by a non-significant recovery trend, occurred in all seasons (and months) except for some winter months. Atmospheric circulation plays a key role in explaining the variability of winds, with the North Atlantic Oscillation positively affecting the annual wind speed, the Southern Oscillation displaying a significant negative relationship with winds in winter, spring and autumn, and the Eastern Atlantic negatively modulating winds in summer.