P2C2: Decomposition and Reconstruction of Drought Variability Across the Continental United States and Northern Mexico

美国西部（美国）在过去的二十年里，墨西哥北部和北方经历了严重和长期的干旱，减少了水资源，增加了野火活动，并引起了人们对水政策是否为足够广泛的未来可能性而设计的关注。 与此同时，美国东部大部分地区经历了百年来的湿润趋势，最小的变暖和反复的洪水，但古证据表明，该地区仍然容易发生毁灭性的十年干旱。目前尚不清楚这些对比鲜明的趋势是否在动态上相关，以及它们是否受到人为强迫的帮助。激发这项研究的低频水文气候事件在观测记录中是异常的，但古气候重建表明，极端的，长期的水文气候波动经常自然发生。该项目的目的是将一系列空间连续干旱指标扩展到至少1,200年。该项目将使用新的网格重建过去一千年的年度水文气候变化，以更好地了解美国和北方墨西哥的低频、十年尺度水文气候变化的驱动因素，使用三种研究方法：（1）确定近几十年来人为变暖在多大程度上改变了观测到的土壤湿度的千年地位;（2）重建美国和北方墨西哥过去一千年来年际到数十年干旱变化的主要模式，特别关注对加州水资源至关重要的模式和反映东西偶极子的模式，这可能有助于了解观察到的几十年趋势;以及（3）重建和诊断美国干旱变化的东西偶极子，并确定自然多-这种模式的十年变化映射到预测的气候趋势上。2更广泛的影响包括对早期职业科学家的支持，以及对水资源管理者有价值的美国过去一千年水文气候变化的区域和大陆尺度重建的发展。

The western United States (U.S.) and northern Mexico have experienced intense and prolonged droughts over the past two decades that have reduced water resources, enhanced wildfire activity, and raised concerns regarding whether water policies are designed for a sufficiently wide range of future possibilities. Concurrently, much of the eastern U.S. experienced a centennial wetting trend, minimal warming, and repeated floods, but paleo evidence indicates that this region is nonetheless prone to devastating decade-scale droughts. It is unclear if these contrasting trends are dynamically related and whether they have been aided by anthropogenic forcing. The observed low-frequency hydroclimate events that motivate this research are abnormal in the observational record, but paleoclimate reconstructions indicate that extreme, prolonged swings in hydroclimate often occur naturally. The aim of the project is to extend a range of spatially continuous drought metrics for at least 1,200 years.This project will use new gridded reconstructions of annual hydroclimatic variability over the past millennium to better understand the drivers of low frequency, decadal scale hydroclimate variability across the US and northern Mexico using three research approaches: (1) determine the degree to which anthropogenic warming has altered the millennial standing of observed soil-moisture in recent decades; (2) reconstruct the leading modes of interannual to multi-decadal drought variability over the past millennium across the U.S. and northern Mexico, with particular focus on a mode critical for California water resources and a mode reflecting an east-west dipole that may lend insights regarding observed multi-decade trends; and (3) reconstruct and diagnose the east-west dipole in drought variability across the U.S. and determine how the expected magnitude of natural multi-decade variations in this mode map onto projected climate trends.The broader impacts involve support for an early career scientist and the development of regional- and continental- scale reconstructions of hydroclimate variability in the United States spanning the past millennium of value to water resource managers.