CAUSES AND PREDICTABILITY OF THE 2012 GREAT PLAINS DROUGHT
CAUSES AND PREDICTABILITY OF THE 2012 GREAT PLAINS DROUGHT
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DOI：
10.1175/bams-d-13-00055.1
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发表时间：
2014-02-01
影响因子：
8
通讯作者：
Seager, R.
中科院分区：
文献类型：
--
作者：
Hoerling, M.;Eischeid, J.;Seager, R.
2012年5月至8月期间，中部大平原的降水不足是至少自1895年以来最严重的，使1934年和1936年的沙尘暴夏季黯然失色。在冬季和早春降水接近正常之后，5月突然发生干旱。其直接原因是从墨西哥湾向大平原输送的大气水分减少。通常提供气团抬升和凝结的过程大多不存在，包括春末缺乏锋面气旋，随后由于大规模沉降和大气稳定化，夏季深层对流受到抑制。季节性预报没有预测2012年夏季中部大平原干旱的发展，因此没有预警。气候模拟和实证分析表明，海洋表面温度以及温室气体的变化并没有导致2012年大平原中部夏季降水量大幅减少。然而，对回顾性气候模拟的诊断也揭示了近十年来大平原夏季气候条件向更温暖和更干燥的方向转变，这很可能是由于自然的十年变化。因此，与1980年代和1990年代相比，过去十年发生大平原夏季严重干旱的可能性可能有所增加，2012年夏季所谓的严重干旱尾部风险可能有所增加。然而，在2012年气候模型模拟的范围内，这种极端干旱事件仍然是罕见的。这项研究的结果对美国季节性干旱预测的影响进行了讨论。
Central Great Plains precipitation deficits during May-August 2012 were the most severe since at least 1895, eclipsing the Dust Bowl summers of 1934 and 1936. Drought developed suddenly in May, following near-normal precipitation during winter and early spring. Its proximate causes were a reduction in atmospheric moisture transport into the Great Plains from the Gulf of Mexico. Processes that generally provide air mass lift and condensation were mostly absent, including a lack of frontal cyclones in late spring followed by suppressed deep convection in the summer owing to large-scale subsidence and atmospheric stabilization. Seasonal forecasts did not predict the summer 2012 central Great Plains drought development, which therefore arrived without early warning. Climate simulations and empirical analysis suggest that ocean surface temperatures together with changes in greenhouse gases did not induce a substantial reduction in sum mertime precipitation over the central Great Plains during 2012. Yet, diagnosis of the retrospective climate simulations also reveals a regime shift toward warmer and drier summertime Great Plains conditions during the recent decade, most probably due to natural decadal variability. As a consequence, the probability of the severe summer Great Plains drought occurring may have increased in the last decade compared to the 1980s and 1990s, and the so-called tail risk for severe drought may have been heightened in summer 2012. Such an extreme drought event was nonetheless still found to be a rare occurrence within the spread of 2012 climate model simulations. The implications of this study's findings for U.S. seasonal drought forecasting are discussed.