Loisel Julie, MacDonald Glen M, Thomson Marcus J
Department of Geography, Texas A&M University, Eller O&M Building, College Station TX.
Institute of the Environment and Sustainability, University of California Los Angeles, La Kretz Hall, Los Angeles CA.
PLoS One. 2017 Oct 16;12(10):e0186282. doi: 10.1371/journal.pone.0186282. eCollection 2017.
The American Southwest has experienced a series of severe droughts interspersed with strong wet episodes over the past decades, prompting questions about future climate patterns and potential intensification of weather disruptions under warming conditions. Here we show that interannual hydroclimatic variability in this region has displayed a significant level of non-stationarity over the past millennium. Our tree ring-based analysis of past drought indicates that the Little Ice Age (LIA) experienced high interannual hydroclimatic variability, similar to projections for the 21st century. This is contrary to the Medieval Climate Anomaly (MCA), which had reduced variability and therefore may be misleading as an analog for 21st century warming, notwithstanding its warm (and arid) conditions. Given past non-stationarity, and particularly erratic LIA, a 'warm LIA' climate scenario for the coming century that combines high precipitation variability (similar to LIA conditions) with warm and dry conditions (similar to MCA conditions) represents a plausible situation that is supported by recent climate simulations. Our comparison of tree ring-based drought analysis and records from the tropical Pacific Ocean suggests that changing variability in El Niño Southern Oscillation (ENSO) explains much of the contrasting variances between the MCA and LIA conditions across the American Southwest. Greater ENSO variability for the 21st century could be induced by a decrease in meridional sea surface temperature gradient caused by increased greenhouse gas concentration, as shown by several recent climate modeling experiments. Overall, these results coupled with the paleo-record suggests that using the erratic LIA conditions as benchmarks for past hydroclimatic variability can be useful for developing future water-resource management and drought and flood hazard mitigation strategies in the Southwest.
在过去几十年里，美国西南部经历了一系列严重干旱，期间穿插着强烈的湿润期，这引发了人们对未来气候模式以及在气候变暖条件下天气干扰可能加剧的疑问。在此，我们表明，该地区年际水文气候变率在过去一千年中呈现出显著的非平稳性。我们基于树木年轮对过去干旱情况的分析表明，小冰期（LIA）期间年际水文气候变率较高，类似于对21世纪的预测。这与中世纪气候异常（MCA）相反，MCA期间变率降低，因此尽管其气候温暖（且干旱），但作为21世纪变暖的类比可能会产生误导。鉴于过去的非平稳性，特别是不稳定的小冰期，一种将高降水变率（类似于小冰期条件）与温暖干燥条件（类似于中世纪气候异常条件）相结合的21世纪“温暖小冰期”气候情景代表了一种合理的情况，近期的气候模拟也支持这一点。我们将基于树木年轮的干旱分析与热带太平洋记录进行比较，结果表明，厄尔尼诺 - 南方涛动（ENSO）变率的变化解释了美国西南部中世纪气候异常和小冰期条件之间大部分对比差异。正如最近几项气候模拟实验所示，温室气体浓度增加导致经向海表面温度梯度减小，可能会引发21世纪更大的ENSO变率。总体而言，这些结果与古气候记录表明，将不稳定的小冰期条件作为过去水文气候变率的基准，对于制定美国西南部未来的水资源管理以及干旱和洪水灾害缓解策略可能会有所帮助。
