288 JOURNAL OF CLIMATE VOLUME 19 Extension of Drought Records for Central Asia Using Tree Rings: West-Central Mongolia* N. K. DAVI Tree-Ring Laboratory, Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York G. C. JACOBY Tree-Ring Laboratory, Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York, and Department of Forestry, National University of Mongolia, Ulaanbaatar, Mongolia A. E. CURTIS Tree-Ring Laboratory, Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York N. BAATARBILEG Tree-Ring Laboratory, Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York, and Department of Forestry, National University of Mongolia, Ulaanbaatar, Mongolia (Manuscript received 22 November 2004, in final form 3 August 2005) ABSTRACT Central Asian drought has had drastic impacts on vast regions over recent years. Longer records and insight into temporal drought patterns could aid greatly in anticipating extreme events and agrarian plan- ning. Mongolia is representative of the central Asian region, and tree-ring resources are used herein to extend the climate record and test for solar influence and/or Pacific Ocean teleconnections. Absolutely dated tree-ring-width chronologies from five sampling sites in west-central Mongolia were used in precipi- tation models and an individual model was made using the longest of the five tree-ring records (1340–2002). The tree-ring sites are in or near the Selenge River basin, the largest river in Mongolia and a major input into Lake Baikal in Siberia. Regression models resulted in a reconstruction of streamflow that extends from 1637 to 1997 and explains 49% of the flow variation. Spectral analysis indicated significant variation in the frequencies common to Pacific Ocean variations [Pacific decadal oscillation (PDO) and ENSO] and also some quasi-solar and lunar-nodal periodicities similar to previous Mongolian hydrometeorological recon- structions in eastern Mongolia based on tree rings. 1. Introduction edge and historical records provide partial estimation of drought recurrence (e.g., Mijiddorj and Namhay Drought across central Asia has devastated many re- 1993) but better quantitative information is needed to gions over the last few years and many times in the past. define long-term drought variations in means, ex- Much of Mongolia was especially hard hit with 4 yr of tremes, and trends, and to test for evidence of cyclical extensive drought in 1999–2002. The paucity of long- variations. Human observations leading to hypotheses term records interferes with efforts to anticipate prob- of drought variations need to be supported by quanti- able occurrence and extent of future droughts in central tative reconstructions and analyses of temporal and Asia and in particular Mongolia. Traditional knowl- spatial patterns that may hopefully lead to understand- ing of probable future events. * Lamont-Doherty Earth Observatory Contribution Number Mongolia typifies the steppe terrain and semiarid to 6825. arid continental climate that extends across much of central Asia (Zhang and Lin 1992). Mongolia also typ- ifies large areas of Asia in another way, in that there are Corresponding author address: Nicole Davi, Tree-Ring Labo- ratory, Lamont-Doherty Earth Observatory, Columbia Univer- few long records of hydrometeorological data. Most sity, 61 Route 9W, Palisades, NY 10964. records barely extend beyond 50 yr. Our previous study E-mail: [email protected] demonstrated that tree-ring analysis can be used to re- © 2006 American Meteorological Society Unauthenticated | Downloaded 09/29/21 05:09 AM UTC JCLI3621 15 JANUARY 2006 DAVI ET AL. 289 FIG. 1. Map of Mongolia showing tree-ring sampling sites (triangles), precipitation stations (numbered), and streamflow gauge station (star). construct precipitation and streamflow in eastern Mon- were tested against individual precipitation stations and golia (Pederson et al. 2001) and that there was evidence regional averages of precipitation for the central region supporting quasi-solar and lunar-nodal variations in of Mongolia (Fig. 1). Significant correlations were drought for that region. The streamflow of the Kherlen found and models developed to estimate seasonal pre- River and precipitation for part of the region were re- cipitation using the tree-ring data. We also developed constructed back to 1651. Spectral analysis showed an independent streamflow reconstruction for the Se- quasi-solar and lunar-nodal variability, and the extreme lenge River. The resulting reconstruction, based on five drought of 1999–2002 fit the long-term pattern caused tree-ring chronologies, forms a 360-yr (1638–1997) rec- by the combination of solar (22 and 11 yr) and lunar- ord for streamflow variations of the Selenge River, a nodal (18.6 yr) variations (Pederson et al. 2001). Test- major source of freshwater for Mongolia, as well as the ing of the spatial consistency of such patterns is needed major input to Lake Baikal (Ma et al. 2003). to evaluate their importance. The precipitation models and streamflow reconstruc- tion presented here are based on annual ring-width 2. Tree-ring data variations of moisture-stressed, old-aged trees. We a. Site information sampled nondestructively at several lower-elevation sites where precipitation appears to be the major factor The Zuun Salaa Mod (ZSM) site (Fig. 1, Table 1) was limiting growth. We also sampled at one slightly higher named for a “hundred-branched tree” of old-aged ap- elevation site where the highly permeable rock sub- pearance just to the east of the site. It is greatly revered strate produces an edaphic desert. The tree-ring data by people and draped with cloth and other items placed TABLE 1. Tree-ring site information table. No. of Tree-ring sites Lat (N) Lon (E) Alt (m) trees Years Species EPSa RBARb Undur Ulaan (UU) 48°59Ј 103°14Ј 1400 15 1473–2002 Larix sibirica Ͼ0.96 0.50–0.77 Suulchyin Medee (SM) 49°29Ј 100°50Ј 1800c 15 1573–2002 Larix sibirica Ͼ0.97 0.68–0.84 Khorgo Lava (KL) 48°10Ј 99°52Ј 2060 39 1340–2000 Larix sibirica Ͼ0.92d 0.54–0.78 Telmen Hövöö (TH) 48°46Ј 97°07Ј 1841 16 1638–1998 Larix sibirica Ͼ0.93 0.41–0.69 Zuun Salaa Mod (ZSM) 48°09Ј 100°17Ј 1900 20 1513–2001 Larix sibirica Ͼ0.89 0.45–0.85 a Expressed population signal statistic. b Rbar ϭ the mean correlation coefficient between all tree-ring series used in a chronology. c Estimated from map. d KL Rbar is Ͼ0.92 except for pre-1400s where EPS is 0.81. Unauthenticated | Downloaded 09/29/21 05:09 AM UTC 290 JOURNAL OF CLIMATE VOLUME 19 there for religious purposes. We did not sample this TABLE 2. Five-chronology correlation matrix over common tree or any nearby trees. There is a major road about period 1638–1990. 100 m to the east of the site but little evidence of other UU SM KL TH ZSM disturbance. ZSM is gently sloped (ϳ5°) to the east and UU 1 0.56* 0.27* 0.31* 0.37* sparse grass grows between each tree. There was sub- SM 1 0.42* 0.43* 0.50* stantial heartrot in some of these trees, which fre- KL 1 0.45* 0.62* quently occurs in larch trees throughout Asia, even in TH 1 0.46* dry sites. ZSM 1 Telmen Hövöö (TH, or Telmen Beach; Fig. 1, Table * Significance level (0.05). 1) was the only stand of trees for several tens of kilo- meters in this area. This small forest grows on part of a sand dune complex located next to Telmen Lake. Local dardization is to reduce the effects of age and other residents indicated that there had been some logging nonclimatic factors on the resulting series. The stan- (we saw very few stumps), no fires, and no dramatic dard chronologies were used because we wanted to pre- change in lake levels over the past 60 yr. serve low-frequency variations that would be removed The Khorgo Lava (KL) site (Fig. 1, Table 1), located by prewhitening. All the stands were open canopy and in the Khorgo-Terkhiin Tsagaan Nuur National Park, is the standard chronology is more appropriate than the on a geologically young basaltic lava flow with very ARS chronology for such sites (Cook 1985). little soil development. There has been previous success We tested for autoregressive properties of the tree- in reconstructing drought using trees from such sites ring and meteorological data for the common period (Grissino-Meyer et al. 1997). The extreme dryness of (1945–98). The meteorological data are autoregressive the site likely reduces the prevalence of heartrot in order one based on the Aikaike criteria and three of the these trees, resulting in great longevity (1340–2002). Al- five chronologies are order one. The other two are or- though near a small town, the rugged and rocky terrain der zero. Thus, the data are compatible. We did not appeared to reduce the cutting and disturbance of the prewhiten in making the model because we wanted to site. preserve low-frequency variation in the reconstruction. Undur Ulaan (UU, or Red Hill; Fig. 1, Table 1) is on Individual chronology information and statistics are a steep hill, about 200 m north of a main road. Hillside shown in Table 1. The expressed population signal grazing was the only evidence of disturbance. Trees had (EPS) statistic, a measure of chronology reliability substantial heartrot. (Wigley et al. 1984), is greater than 0.89 over the entire Suulchyin Medee (SM, or Last Statement; Fig. 1, length of each chronology, with the exception of the Table 1) is on the north and west facing slopes of a dry early portion of KL (Table 1). A level of 0.85 is con- ridge with very sparse vegetation. A lot of dieback, sidered to be an indication of satisfactory quality for a attributed to insect infestation, was seen in the canopy; chronology.