Two Types of Flash Drought and Their Connections with Seasonal Drought

Abstract

Flash drought is a rapidly intensifying drought with abnormally high temperature, which has greatly threatened crop yields and water supply, and aroused wide public concern in a warming climate. However, the preferable hydrometeorological conditions for flash drought and its association with conventional drought at longer time scales remain unclear. Here, we investigate two types of flash drought over China: one is high-temperature driven (Type I), while the other is water-deficit driven (Type II). Results show that the frequencies of the two types of flash drought averaged over China during the growing season are comparable. Type I flash drought tends to occur over southern China, where moisture supply is sufficient, while Type II is more likely to occur over semi-arid regions such as northern China. Both types of flash drought increase significantly (p < 0.01) during 1979–2010, with a doubled rise in Type I as compared with Type II. Composite analysis shows that high temperature quickly increases evapotranspiration (ET) and reduces soil moisture from two pentads before the onset of Type I flash drought. In contrast, there are larger soil moisture deficits two pentads before the onset of Type II flash drought, leading to a decrease in ET and increase in temperature. For flash drought associated with seasonal drought, there is a greater likelihood of occurrence during the onset and recovery phases of seasonal drought, suggesting perfect conditions for flash drought during transition periods. This study provides a basis for the early warning of flash drought by connecting multiscale drought phenomena.

摘 要

骤发干旱是一种伴随热浪快速发生发展的干旱, 对作物产量和水资源供给有严重威胁, 并在气候变化研究中引起广泛关注. 然而, 目前骤发干旱发展演变过程中的水文气象特征及其与传统干旱之间的联系仍不明确. 这里, 我们研究了中国区域两类骤发干旱的变化特征, 一类是高温驱动(I 型), 另一类由降水不足驱动(II 型). 结果表明: 在生长季, I 型骤发干旱通常发生在水分供给充足的南方地区, II 型骤发干旱则较易发生在半干旱地区如中国北方. 两类骤发干旱在 1979–2010 年期间均有显著增长, I 型骤发干旱是II型增长速率的两倍. 通过合成分析, 发现 I 型骤发干旱发生时, 高温引起强蒸散发, 并在约 10 天前引发土壤湿度的快速变干. 相比之下, II 型骤发干旱爆发前 10 天已有一定的土壤水分亏缺, 蒸散发减少进而引发高温. 对于发生在季节干旱期间的骤发干旱, 它们更易发生在季节干旱的爆发和恢复阶段, 表明在干湿转换期有利于骤发干旱的发生. 本研究表明, 通过将多尺度干旱现象相联系, 可以为骤发干旱的早期预警研究提供有利信息.