NOAA/WDS Paleoclimatology - Cleaveland et al. 2002 Durango Mexico Precipitation Reconstructions

Earlywood width chronologies from Douglas-fir tree rings were used to reconstruct winter (November–March) precipitation for more than 600 years over Durango, Mexico. The tree-ring data were obtained from two sites of long-lived Douglas-fir in northern and southern Durango and the seasonal climatic precipitation data were regionally averaged from five weather stations well distributed across the state. The averaged earlywood chronology accounted for 56% of the variance in instrumental November–March precipitation 1942–1983. We validated the reconstruction against independent precipitation records. The worst winter drought of the 20th century in Durango occurred 1950–1965. However, the reconstruction indicates droughts more severe than any witnessed in the 20th century, e.g., the 1850s–1860s, and the megadrought in the mid- to late-16th century. Reconstructed winter precipitation 1540–1579 shows 33 of 40 years were dry. Persistent drought may be linked to extended La Niña episodes. The Tropical Rainfall Index (TRI) correlates well with instrumental and reconstructed winter precipitation (r = 0.49 and 0.55, respectively), reflecting the strong ENSO modulation of cool season climate over northern Mexico. The ENSO teleconnection varies through time, with TRI-reconstructed precipitation correlations ranging from 0.78 to 0.27 in five periods 1895–1993. The 1942–1983 winter observed and reconstructed Durango data correlate well with the corresponding seasonalization of the All-Mexico Rainfall Index (AMRI; r=0.68, P<0.0001 and r=0.70, P<0.001, respectively), indicating that both the observed and the reconstructed precipitation often reflect broad-scale precipitation anomalies across Mexico. New long Douglas-fir and baldcypress tree-ring chronologies are now available for central and southern Mexico near major population centers, allowing the exploration of relationships between drought, food scarcity, and social and political upheaval in Mexican history.

以花旗松（Douglas-fir）年轮的早材宽度年表为基础，本研究重建了墨西哥杜兰戈州过去600余年的冬季（11月至次年3月）降水序列。该树轮数据采自杜兰戈州南北两地的两处长寿花旗松样点，而季节性气候降水数据则由全州分布均匀的5个气象站的观测值区域平均得到。该平均早材年表能够解释1942年至1983年器测冬季（11月至次年3月）降水方差的56%。我们通过独立降水记录对该重建序列进行了验证。杜兰戈州20世纪最严重的冬季干旱发生于1950年至1965年期间，但重建结果显示，历史上曾出现过比20世纪任何一次干旱都更为严重的旱情，例如19世纪50年代至60年代的干旱，以及16世纪中后期的特大干旱。1540年至1579年的重建冬季降水序列显示，40年中有33年为干旱年份。持续性干旱可能与持续发生的拉尼娜（La Niña）事件存在关联。热带降水指数（Tropical Rainfall Index, TRI）与器测及重建的冬季降水序列均呈现显著相关（相关系数分别为0.49和0.55），这反映出厄尔尼诺-南方涛动（ENSO）对墨西哥北部冷季气候具有强烈的调制作用。ENSO遥相关关系随时间发生变化，在1895年至1993年的5个时段内，热带降水指数与重建降水序列的相关系数介于0.78至0.27之间。1942年至1983年杜兰戈州冬季的器测与重建降水数据，与全墨西哥降水指数（All-Mexico Rainfall Index, AMRI）的对应季节序列相关性良好（相关系数分别为0.68，P<0.0001；以及0.70，P<0.001），这表明器测与重建的降水序列均能够反映墨西哥全境大范围的降水异常特征。目前已获取墨西哥中部及南部人口主要聚居区附近的长序列花旗松与落羽杉（baldcypress）树轮年表，这为探究墨西哥历史上干旱、粮食短缺与社会政治动荡之间的关联提供了研究基础。