Extension of Drought Records for Central Asia Using Tree Rings: West-Central Mongolia*

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 planning. 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 precipitation 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 reconstructions in eastern Mongolia based on tree rings.

A tree-ring-based reconstruction of the Yimin River annual runoff in the Hulun Buir region, Inner Mongolia, for the past 135 years

“…For instance, the reconstructed values 4.99 (1984) and 4.914 (1990) are lower than the recorded values (lg-transformed) of 5.17 and 5.1, respectively. A similar phenomenon is shown by a tree-ring-based streamflow reconstruction for west-central Mongolia [31].…”

“…Significant cycles were found for periods of ~20, 14-16 and 4-8 years. Similar cycles were detected in the reconstructions of the Kherlen River [44] and the Selenge River [31]. In addition, the influence of the Pacific Decadal Oscillation (PDO) [45,46] and El Niño-Southern Oscillation (ENSO) [47] on the Selenge River basin, west central Mongolia, has been investigated [31].…”

“…Because annual runoff varies over a broad range (Figure 5), the water levels that influence ring widths if the amount of precipitation (and the resulting runoff) is high do not produce the same response rates that occur as a result of increases at lower levels of precipitation because the trees experience other growth restrictions, such as those resulting from the nutrient supply or internal biochemical limitations [31]. For this reason, the relationship between runoff and tree-ring data could be nonlinear.…”

“…One dataset, from a location approximately 1300 km west of our study area, is a reconstruction of the April-October streamflow of the Selenge River, based on tree rings in west-central Mongolia [31]. The other dataset, from a location approximately 700 km southwest of our study area, is a reconstruction of the August-July streamflow of the Kherlen River, based on tree rings in northeastern Mongolia [44].…”

“…The peaks and valleys in the Z-scores of our Yimin River reconstruction, the PC index and the Selenge River reconstruction match each other very accurately, with different degrees of bidecadal-scale variations present since 1868 (Figure 8). On an interannual scale, extreme droughts lasting five years occurred in the reconstructions of the Yimin River, Kherlen River [44] and Selenge River [31] during 1905-1909, 1903-1907 and 1901-1905, respectively. The wetter periods occurring in the 1990s were 1990-1991, 1991-1995 and 1990-1994, respectively.…”