Reconstruction of a 1436‐year soil moisture and vegetation water use history based on tree‐ring widths from Qilian junipers in northeastern Qaidam Basin, northwestern China

Abstract

Tree-ring widths have been used widely in studies of environmental changes and reconstructions of past climate. Eleven tree-ring chronologies of approximately 800-1500 years long were developed from Qilian junipers (Sabina przewalskii Kom.) for northeastern Qaidam Basin, along the margin of the Qinghai-Tibetan Plateau. Previous studies have revealed that water usage stress is the most limiting factor for tree growth in the study region. To evaluate the impact of the combined effects of temperature and precipitation changes over time, we performed water balance modelling using 1955-2002 meteorological data. We found that the tree-ring widths were strongly correlated with variables representing soil moisture conditions obtained from the water balance model. Specifically we considered actual evapotranspiration (AE) to represent the combined effect of water use demand and moisture availability, deficit as the difference between potential evapotranspiration (PE) and AE to represent the severity of water use stress, and relative soil moisture as the measure of moisture availability. For certain individual monthly and seasonal combinations, the tree-ring chronologies explained up to 80% of the variation in the soil moisture variables in regression analysis, indicating very good potential for reconstruction of regional soil moisture conditions in the past. These soil moisture variables outperformed precipitation and Palmer's drought severity index in most cases. We reconstructed the soil moisture conditions from 566 AD to 2001, which revealed major dry and wet periods and a general trend toward a wetter condition during the most recent 300 years. By comparing with other proxies in the region, we concluded that the moisture conditions reconstructed from tree-ring widths very well reflected the climate variability at the interannual and interdecadal scales.

Early summer temperature reconstruction in the eastern Tibetan plateau since ad 1440 using tree-ring width of Sabina tibetica

“…Tree rings, as an annually resolved proxy record, have been increasingly used to reconstruct past climate changes on the TP (e.g., Bräuning and Mantwill 2004;Gou et al 2008;Liang and Eckstein 2009;Liang et al 2008;Liu et al 2007;Liu et al 2006;Shao et al 2005;Shi et al 2010;Wang et al 2009;Yang et al 2009;Yin et al 2008;Zhang et al 2003;Zhu et al 2008). For example, Liu et al (2007) reconstructed winter temperature variations since AD 1000 for the middle Qilian Mountains using Sabina przewalskii.…”

Reconstruction of biological drought conditions during the past 2847 years in an alpine environment of the northeastern Tibetan Plateau, China, and possible linkages to solar forcing

“…ringwidth chronologies found in the eastern Qaidam Basin of the northeastern Tibetan Plateau, a common feature in the relationships between tree growth and climate variables is a strong positive correlation with precipitation in the late spring and early summer (esp. May and/or June) in conjunction with a negative correlation with temperature for the same time period (e.g., Shao et al, 2010;Shao et al, 2005;Sheppard et al, 2004;Yin et al, 2008;Zhang et al, 2003). This has also been discovered for a variety of coniferous species in other areas of the northeastern and eastern Tibetan Plateau, such as Qilian Mountains (Zhang et al, 2011, in May-June, approx.…”

“…McCabe and Markstrom (2007) stated that a WHC of 150 mm should suit most conditions. Yin et al (2008) discovered that the correlation between the simulated soil moisture and tree growth in Delingha became stronger as WHC increases, mostly due to the fact that a small WHC value could lead to rapid depletion of soil moisture and keep it at zero in this semi-arid environment. Therefore, the WHC value was set to 100 mm in this study for all simulations, considering steep slopes and thin soil layers at the sampling sites.…”

“…In other words, early growing-season moisture condition can be considered as the ultimate factor regulating tree growth in this region. In an earlier study (Yin et al, 2008), it was found that the simulated moisture conditions in the eastern Qaidam Basin (Delingha) using a water balance model were strongly correlated with the radial growth of Qilian juniper, outperforming similar analyses using precipitation or Palmer's Drought Severity Index (PDSI, Palmer, 1965) data. However, whether the simulated moisture variables (e.g., soil moisture, and moisture deficit and surplus) represented the conditions at the weather station on the foothills or those at the tree ring sampling sites was a question unanswered.…”

“…according to Yeh and Gao (1979). Some of the tree ring samples (DLH1-6) were used in an earlier study by Yin et al (2008), while the archaeological sites (no. 1-13) and DLH4W were described in Shao et al (2010).…”