Flash drought is a type of drought that develops quickly (usually within 2–4 weeks) in contrast to conventional, slowly evolving drought. Due to its sudden onset, flash drought is more difficult to predict and can cause major agricultural losses if it is not forecasted in a timely manner. To improve our ability to predict flash drought, we develop a subseasonal tool to predict areas susceptible to flash drought development using the Phase 2 of the North American Land Data Assimilation System (NLDAS-2) data. The tool calculates the rapid change index (RCI) using 7-day mean evapotranspiration anomalies. RCI is the accumulated magnitude of moisture stress changes (standardized differences) occurring over multiple weeks, and drought is likely to develop when RCI is negative. Since RCI changes with time, like all drought variables, it is difficult to capture drought development signals by monitoring RCI maps. In order to create an intuitive drought prediction map that directly depicts drought tendency, we use a threshold method to identify grid points with large decreases of 7-day mean evapotranspiration anomaly (i.e., RCI less than −0.5) in the last 30 days and under the condition that 3-month standardized precipitation index is less than −0.4. The real-time tool started running on 1 April 2018 at the NOAA Climate Prediction Center (CPC) and has been used to support CPC’s Monthly Drought Outlook efforts. The performance of the tool is evaluated using both retrospective and real-time predictions. The assessment shows promising results in predicting potential flash drought development, and the interplay between precipitation and high temperatures appears to be a challenge for flash drought prediction.

中文翻译：

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暴发干旱易感区域的实时预测

与常规的，缓慢发展的干旱相比，闪旱是一种发展迅速（通常在2至4周内）的干旱。由于突发性干旱，突发干旱更加难以预测，如果不及时进行预测，可能会造成重大农业损失。为了提高我们预测山洪暴发的能力，我们开发了一个亚季节工具，使用北美土地数据同化系统（NLDAS-2）数据的第2阶段来预测易受山洪干旱发展的地区。该工具使用7天的平均蒸散量来计算快速变化指数（RCI）。RCI是数周内发生的水分胁迫变化（标准差）的累积量，当RCI为负时，干旱很可能发生。由于RCI会像所有干旱变量一样随时间变化，通过监视RCI图很难捕获干旱发展信号。为了创建直接描述干旱趋势的直观干旱预测图，我们使用阈值方法来识别在过去30天及以下的7天平均蒸发蒸腾异常（即RCI小于-0.5）大幅减少的网格点3个月标准降水指数小于-0.4的条件。该实时工具于2018年4月1日在NOAA气候预测中心（CPC）开始运行，并已用于支持CPC的每月干旱展望工作。使用回顾性和实时预测来评估工具的性能。评估显示，在预测潜在的山洪干旱发展方面，前景可观，