Californian hydroclimate is strongly seasonal and prone to severe water shortages. Recent changes in climate trends have induced shifts in seasonality, thus exacerbating droughts, wildfires, and adverse water shortage effects on the environment and economy. Previous studies have examined the timing of the seasonal cycle shifts mainly as temperature driven earlier onset of the spring season. In this paper, we address quantitative changes in the onset, amounts, and termination of the precipitation season over the past 6 decades, as well as the large‐scale atmospheric circulation underpinning the seasonal cycle changes. We discover that the onset of the rainy season has been progressively delayed since the 1960s, and as a result the precipitation season has become shorter and sharper in California. The progressively later onset of the rainy season is shown to be related to the summer circulation pattern extending into autumn across the North Pacific, in particular, a delay in the strengthening of the Aleutian Low and later southward displacement of the North Pacific westerlies.

中文翻译：

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加利福尼亚雨季的较晚发作

加利福尼亚州的气候气候具有强烈的季节性，容易出现严重的水短缺。气候趋势的最新变化已导致季节变化，从而加剧了干旱，野火以及对环境和经济的不利缺水影响。先前的研究已经检查了季节性周期变化的时间，主要是因为温度驱动了春季的较早发作。在本文中，我们讨论了过去6年中降水季节的开始，数量和终止的定量变化，以及支撑季节周期变化的大规模大气环流。我们发现，自1960年代以来，雨季的开始已逐渐推迟，结果加利福尼亚的降水季节变得越来越短和越来越尖锐。