基于复合事件指数的西北地区高温干旱复合事件风险评估

基于标准化降水指数SPI和标准化温度指数STI构建了两个监测高温干旱复合事件指数：标准化复合事件指数SCEI和混合干热事件指数BDHI，并评估了SCEI和BDHI在西北地区高温干旱复合事件中的监测能力。以严重程度、面积覆盖百分比和发生频率分析了高温干旱复合事件的风险变化。结果表明：由于BDHI充分考虑了不同干热条件之间的相关性，其在西北地区监测高温干旱复合事件的能力明显优于SCEI，而SCEI存在将湿热状况误判为高温干旱复合事件的情况。相较于1982—1993年，1994—2022年西北地区发生高温干旱复合事件的严重程度、范围和频率更高；1994—2022年西北地区发生轻度、中度、重度等级以上的高温干旱复合事件的面积占比分别为35%、25%、10%；新疆中部、甘肃北部和东部、青海南部和陕西大部分地区在1982—1993年几乎未发生过重度等级以上的高温干旱复合事件，但上述地区在1994—2022年的发生频率明显增加。

Risk assessment of compound dry-hot events in northwest China based on compound event indexes

Two compound dry-hot event indexes, i.e., standardized compound event indicator (SCEI) and blended dry and hot events index (BDHI), were calculated based on the standardized precipitation index (SPI) and the standardized temperature index (STI). Then, the performance of SCEI and BDHI in monitoring the compound dry-hot events over northwest China was evaluated, by which the risk changes of compound dry-hot events were analyzed based on the severity, area coverage percentage and frequency. The results show that the BDHI has a better performance in monitoring the compound dry-hot events over northwest China than SCEI, due to its coverage of diverse correlations between different dry and hot conditions; whereas the SCEI may misjudge the hot and wet conditions as compound dry-hot events. The severity, area coverage percentage and frequency of compound dry-hot events were higher during the period of 1994-2022 than that of 1982-1993 over northwest China. During the period of 1994-2022, the area proportions of compound dry-hot events with the light, moderate, and severe categories were 35%, 25%, and 10%, respectively. Notably, the central part of Xinjiang, northern and eastern Gansu, southern Qinghai, and most of Shaanxi have hardly experienced compound dry-hot events above the severe level during the period of 1982-1993; however, the frequency of these events has significantly increased in these areas during the period of 1994-2022.