Little change in global drought over the past 60 years
Little change in global drought over the past 60 years
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DOI：
10.1038/nature11575
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发表时间：
2012-11-15
期刊：
影响因子：
64.8
通讯作者：
Roderick, Michael L.
中科院分区：
文献类型：
--
作者：
Sheffield, Justin;Wood, Eric F.;Roderick, Michael L.
由于气候变化，预计未来干旱的频率和严重程度将会增加，这主要是区域降水量减少的结果，但也是全球变暖导致蒸发量增加所致（1 - 3）。先前对20世纪末和21世纪初干旱历史变化的评估表明，这种情况可能已经在全球范围内发生。特别是，帕尔默干旱严重程度指数（PDSI）的计算显示，自20世纪70年代以来全球水分减少，干旱面积相应增加，部分原因可归结为全球变暖（4，5）。PDSI的简单性，即通过由月降水量和温度数据驱动的简单水平衡模型计算得出，使其成为大规模干旱评估中一个有吸引力的工具，但在气候变化背景下可能会产生有偏差的结果（6）。在此我们表明，先前报道的全球干旱增加情况被高估了，因为PDSI使用了一种简化的潜在蒸发模型（7），该模型仅对温度变化做出反应，因此对近几十年来的全球变暖做出了错误反应。基于考虑了可用能量、湿度和风速变化的基本物理原理（8）进行的更符合实际的计算表明，过去60年干旱情况几乎没有变化。这些结果对我们如何解读全球变暖对水文循环及其极端情况的影响具有启示意义，并且可能有助于解释为什么基于树木年轮数据的古气候干旱重建近年来与基于PDSI的干旱记录不一致（9，10）
Drought is expected to increase in frequency and severity in the future as a result of climate change, mainly as a consequence of decreases in regional precipitation but also because of increasing evaporation driven by global warming(1-3). Previous assessments of historic changes in drought over the late twentieth and early twenty-first centuries indicate that this may already be happening globally. In particular, calculations of the Palmer Drought Severity Index (PDSI) show a decrease in moisture globally since the 1970s with a commensurate increase in the area in drought that is attributed, in part, to global warming(4,5). The simplicity of the PDSI, which is calculated from a simple water-balance model forced by monthly precipitation and temperature data, makes it an attractive tool in large-scale drought assessments, but may give biased results in the context of climate change(6). Here we show that the previously reported increase in global drought is overestimated because the PDSI uses a simplified model of potential evaporation(7) that responds only to changes in temperature and thus responds incorrectly to global warming in recent decades. More realistic calculations, based on the underlying physical principles(8) that take into account changes in available energy, humidity and wind speed, suggest that there has been little change in drought over the past 60 years. The results have implications for how we interpret the impact of global warming on the hydrological cycle and its extremes, and may help to explain why palaeoclimate drought reconstructions based on tree-ring data diverge from the PDSI-based drought record in recent years(9,10).