Guang Bao

Tree-ring hydrologic reconstructions for the Heihe River watershed, western China since AD 1430

Based on the tree-ring-width analysis, the total precipitation from previous July to current June of the Qilian Mountains from 1634 to 2000 AD and the average runoff from previous September to current June in the middle section of the Heihe River from 1430 to 2007 have been reconstructed. This allowed detailed examination of the hydrologic history of the watershed of the Heihe River in western China. Precipitation, runoff and groundwater level were found to be significantly correlated with each other on the decadal scale. The three curves display quite synchronous trends of natural variation before AD 1940 to present before the onset of man-made disturbances. A remarkable period is AD 1925-1940 when the precipitation is low in the upper section, the runoff decreases in the middle section, and the groundwater level declines in the downstream section. After 1940, the groundwater level shows a lag effect, which may be a result of high water consumption in the middle and downstream sections. All three tree-ring based hydrologic indices commonly display the most significant periodicities around 80 (78-82), 50 (49-58) and 2 year. These cycles correspond to large-scale oscillation found in the climate system and appear mainly related to ocean-atmosphere interaction.

Mongolian pines (Pinus sylvestris var. mongolica) in the Hulun Buir steppe, China, respond to climate in adjustment to the local water supply

The growth response of Mongolian pine (Pinus sylvestris var. mongolica) to climate was studied at three sites in the Hulun Buir steppe on the eastern Mongolian Plateau, China. Correlation analysis revealed two patterns of response: (1) trees on two sites in the upstream section of the Yimin River are strongly limited by temperature and precipitation during the growing season from April to September, and (2) trees in the convergence area of the downstream section of the Yimin River and of the midstream section of the Hailar River are sensitive to precipitation during winter (December–January) and early spring (April) as well as to the early growing season temperature (April and June). These responses can be attributed to the positions where groundwater, recharged by the runoff from summer to autumn (July–September), could supply sufficient water needed for tree growth. Therefore, the patterns of growth–climate responses and of climate variation trends in this steppe region should be considered for the management and afforestation of Mongolian pines.

Droughts and broad-scale climate variability reflected by temperature-sensitive tree growth in the Qinling Mountains, central China

The relationship between temperature and drought was investigated using the temperature-sensitive growth of Larix chinensis Beissn in the Qinling Mountains, central China. Extremely high tree-ring width index values (TRWI) agreed well with dry conditions defined by the dryness-wetness index (DWI) obtained from data in Chinese historical documents and climate-related papers between 1814 and 1956 (before the short of instrumental measurements); the reverse applied to extremely low TRWI values. The main severe drought epochs occurred from the late 1850s to the 1870s, the 1920s to 1930s and in the 2000s, whereas wet spells occurred from 1817–1827 and 1881–1886. The droughts in the 2000s exhibited a similar pattern as the ones from the 1920s to 1930s, with obviously an increasing temperature. The variation of tree growth agreed well with other reconstructed temperature series from nearby and remote regions, suggesting that Larix chinensis could respond to broad-scale climate variability. The longest cold interval, 1817–1827, could be associated with the influence of the Tambora eruption in 1815.

TREE-RING BASED JUNE-JULY RUNOFF RECONSTRUCTION FOR THE DATONG RIVER WATERSHED, WESTERN CHINA SINCE AD1525: TREE-RING BASED JUNE-JULY RUNOFF RECONSTRUCTION FOR THE DATONG RIVER WATERSHED, WESTERN CHINA SINCE AD1525

A tree-ring chronology has been built up based on the tree-ring samples from the Qilian Mountains.Response analysis showed that there is significant relationship between the tree-ring width and the June to July runoff of the Datong River watershed.Based on the analysis,a transfer function was designed to reconstruct the total runoff from June to July of the Datong River during the period 1525—2009.There are 5 wet and 5 dry periods in the reconstructed runoff history.The wet periods are 1530—1555,1576—1586,1733—1760,1776—1786,1855—1912,and the dry periods 670—1680,1691—1730,1814—1836,1926—1942,1964—1978 respetively.The reconstructed series also displayed that the standard deviations in the dry periods are higher than the wet periods,and the extreme dry and wet periods have the highest standard deviation.The reconstructed June-July runoff series shows significant periodicities around 2(2.04~2.3),50(50~57),100,133 and 200years.