Increased winds in California's Channel Islands; Evaluation of trends in reanalysis model back-casts over the last half century with implications for human impacts

As elsewhere, in the Southern California Bight (SCB) the role of coastal winds in driving local ocean circulation has lead to extensive research on the character of the atmospheric boundary layer, and the recognition that wind stress and curl have increased in the recent past. However, around Northern Channel Islands in the SCB, local mariners have claimed that recently conditions have gotten perceptibly windier. The general pattern of winds in this area include strong equartorward flow along the central California coast outside the SCB and discretely weaker flow in the inner SCB with a pronounced transition south and east of Point Conception. Increased surface winds have numerous implications for local commerce and maritime safety, including limitations on days at sea by fishermen, tourists and commercial traffic. However, human perception of environmental conditions are often biased by perceptions of extreme events as representative of larger scale or longer term conditions. To evaluate if recent perceptions are accurate, we evaluated trends in surface winds generated by NCAR/NCEP and European Center for Medium Range Weather Forecasts (ECMWF) reanalysis models. Reanalysis back-casts revealed that indeed surface winds in the areas of the outer Southern California Bight are increasingly windy on average, and that averages are increasing due to increasing frequency of wind events, rather than the entire distribution of winds shifting to higher speeds. In some localized areas the number of days within a year that exceed 20knots (10.31 m/s) on average are increasing at a rate of one additional day per year in the NCAR/NCEP data. The utility of 20knots is this is wind speed that can trigger a small craft warning from the US Coast Guard, and which will in turn affect human activity on the sea. The spatial distribution of the increasing trends indicates that there is a focus of increasing winds to the South of Point Conception and North West of San Nicolas Island within the Southern California Bight. The nature of wind back-casts with reanalysis models demands a significant effort at data validation, which in this case was addressed with comparisons among models and with buoy and land station wind time series. The comparison process revealed helpful insights into strengths, weaknesses and general utility for local users of the reanalysis products.