Drought intensity and duration in southern California, USA during the 21st century has been exceptional, and the changing climate dynamics of drought in this arid and semiarid region have been linked to anthropogenic warming. We examine the frequency, intensity, and persistence of drought in southern California's two climatic divisions during 1900–2022 and use the monthly instrumental record of the Palmer Drought Severity Index (PDSI) to track how drought events have changed. We introduce an empirical definition of “hot drought” by combining mean summer PDSI values with standardized scores of mean summer minimum temperature. Droughts in southern California, USA have become increasingly more severe, frequent, and long-lived in the 21st century. Moderate drought conditions (PDSI < −2) were recorded during more than half of the months in the decade ending in 2020. Similarly, hot droughts, droughts associated with both water deficits and significantly above-normal temperatures, have become increasingly frequent in recent decades. By the 21st century, hot droughts were occurring in approximately half of the summers. Our findings support the idea that anthropogenic warming results in a changing drought climatology for arid and semiarid regions of southern California and that hot droughts will likely become the dominant drought type.

21世纪美国加利福尼亚州南部的干旱强度和持续时间非同寻常，该干旱和半干旱地区干旱气候动态的变化与人为变暖有关。我们研究了 1900 年至 2022 年期间南加州两个气候分区的干旱频率、强度和持续性，并使用帕尔默干旱严重程度指数(PDSI) 的每月仪器记录来跟踪干旱事件的变化。我们通过将夏季平均 PDSI 值与夏季平均最低气温的标准化得分相结合，引入了“炎热干旱”的经验定义。进入21世纪，美国南加州的干旱变得越来越严重、频繁和持久。截至 2020 年的十年中，超过一半的月份记录了中度干旱（PDSI < -2）。同样，近几十年来，炎热干旱、与缺水和气温显着高于正常温度相关的干旱也变得越来越频繁。到了21世纪，大约一半的夏季发生炎热干旱。我们的研究结果支持这样的观点，即人为变暖导致南加州干旱和半干旱地区的干旱气候发生变化，并且热干旱可能会成为主要的干旱类型。