PDSI variations at Kongtong Mountain, China, inferred from a 283-year Pinus tabulaeformis ring width chronology

Pinus tabulaeformis ring widths were used to reconstruct mean Palmer Drought Severity Indices (PDSIs) from May to July for each of the past 283 years for Kongtong Mountain, China. A calibration model for the period from 1940 to 2005 explains 66.4% (or 65.9% after adjusting for the loss of the degrees of freedom) of the actual PDSI variance. The reconstructed Kongtong Mountain PDSIs could be representative of the moisture conditions of the entire Loess Plateau. The reconstruction captures a severe 1927&ndash;1930 drought event that was widespread across all of northern China. After 11‐year moving average, the reconstructed Kongtong PDSI was found to compare well with other tree ring‐based temperature reconstructions from both Huanglong (in the eastern part of the Chinese Loess Plateau) and Hokkaido, Japan. This result indicates that high temperatures may be a major contributor to the severity of dryness at low frequencies. Significant 93.33‐year and approximate 2‐year cycles were observed in the Kongtong tree ring chronology.</p

A simple and rapid preparation of pure cellulose confirmed by monosaccharide compositions, delta C-13, yields and C%

A two-step method to extract pure cellulose from tree rings is presented in this study. The method employs the reagents diglyme (diethylene glycol dimethyl ether), hydrochloric acid and sodium chlorite in a 6-h reaction using ordinary equipment. Through separation of the chemical compositions (monosaccharides) using liquid chromatography, the product of this method is shown to contain only glucose from pure cellulose. In contrast, the chemical composition of the &quot;alpha-cellulose&quot; extract obtained by the traditional Jayme-Wise method is primarily glucose and mannose, which may come from hemicelluloses. These results are also verified by comparing the stable carbon isotope ratio (delta C-13), yields and percentage of carbon (C%) of the product extracted by this method and &quot;alpha-cellulose&quot; for different tree species. The results suggest that this method is simple, rapid and appropriate for processing large numbers of small wood samples to develop tree-ring isotope series for high-resolution paleoclimatic research with softwood trees.</p

Reconstruction of drought variability in North China and its associationwith sea surface temperature in the joining area of Asia andIndian–Pacific Ocean

Using tree-ring data from the northernmost marginal area of the East Asian summer monsoon (EASM) in North China, May–July mean Palmer drought severity index (PDSI) was reconstructed back to 1767 AD. The reconstruction captured 52.8% of the variance over the calibration period from 1945 to 2005 AD and showed pronounced pluvial periods during 1850–1905, 1803–1811 and 1940–1961 and dry periods during 1814–1844, 1916–1932 and 1984–2012. These anomalous periods have previously been reported in other parts of North China. Spatial correlation analyses and comparisons with other hydroclimatic indices in North China indicated that our new PDSI reconstruction could represent spatial and temporal drought variability in this region well. Our work also suggested that the drying tendency currently observed in the northern part of North China (including the study area) is consistent with the weakening of the EASM. Meanwhile the drying trend was seemingly restrained at present in the southern part of North China. Spatial correlation patterns with global sea surface temperature (SST) indicated that the regional hydroclimatic variability in North China was tightly linked to SST over the joining area of Asia and Indian–Pacific Ocean (AIPO), especially over the tropical western Pacific. When SST from prior November to current July (NJ-SST) in the AIPO area was anomalously high (low), the thermal contrast between Asian land and ocean was weakened (strengthened), and the EASM was correspondingly weakened (strengthened), thereby causing droughts (pluvials) in North China. The results of this study do not only provide useful information for assessing the long-term climate change in North China, but also suggest that abnormal variability in NJ-SST over the AIPO area could be used to forecast hydroclimatic conditions in North China

Geomorphic, hydroclimatic and hydrothermal controls on the formation of lithium brine deposits in the Qaidam Basin, northern Tibetan Plateau, China

Qaidam Basin is a hyperarid inland basin with an area of 121 x 10(3) km(2) located on the northern Tibetan Plateau. Today, one fourth of the basin is covered by playas and hypersaline lakes. Nearly 80% of brine lithium found in China is contained in four salt lakes: Bieletan (BLT), DongTaijinaier (DT), XiTaijinaier (XT) and Yiliping (YLP). In the past decade, great attention was paid to improving the technology for the extraction of lithium from the brine deposits, but studies on origin and mode of formation of the brine deposits remained limited. Our recent investigations found that: (1) similar to 748.8 t of lithium was transported annually into the lower catchment of the four salt lakes via the Hongshui-Nalinggele River (H-N River), the largest river draining into the Qaidam Basin, (2) Li+-rich brines are formed only in salt lakes associated with inflowing rivers with Li+ concentrations greater than 0.4 mg/L, and (3) the water Li+ concentration is positively correlated with both the inflowing river and the associated subsurface brine, including saline lakes with low lithium concentrations. These findings clearly indicate that long-term input of Li+ from the H-N River controls the formation of lithium brine deposits. Here we determine that the source of the lithium is from hydrothermal fields where two active faults converge in the upper reach of the Hongshui River. The hydrothermal fields are associated with a magmatic heat source, as suggested by the high Li+ and As3+ content water from geysers. Based on the assumption of a constant rate of lithium influx, we estimate that the total reserves of lithium were likely formed since the postglacial period. Our data indicate that lithium reserves in each of the four salt lakes depend on the influx of Li+-bearing water from the H-N River. The data also suggest that during the progradation of the alluvial Fan I, the H-N River drained mostly into the BLT salt lake until the Taijinaier River shifted watercourse to the north and began to feed the salt lakes of the DT, XT and YLP, alongside with the Fan II progradation. The inference is consistent with stratigraphic evidence from the sediment cores of the four salt lakes. One of the major findings of our work is the importance of the contrasting hydroclimatic conditions between the high mountains containing ice caps and the terminal salt lakes. The greater than 4000 m of relief in the watershed enables a massive amount of ions, such as K+, to be weathered and transported together with detrital material from the huge, relatively wet alpine regions to the hyperarid terminal basins, where intense evaporation rapidly enriches the lake water, resulting in evaporite deposition and associated K+- and Li+-rich brine deposits.</p

Annual precipitation variability inferred from tree-ring width chronologies in the Changling-Shoulu region, China, during AD 1853-2007

On the basis of a significant correlation between the tree-ring width series from Changling-Shoulu (CLSL) in north-central China and observed instrumental data, the annual total precipitation of the previous July to the current June was reconstructed since 1853 for the studied region, with the predictor variables accounting for 41.2% of the variance in the precipitation data. Distinct wet periods with precipitation levels greater than the mean (315 mm) occurred in 1864-1876 and 1934-1960. Notable dry periods with precipitation less than the mean occurred in 1877-1888 and 1923-1933. The precipitation fluctuated dramatically during 1940-1970, and became relatively stable around the mean value from 1960. The CLSL precipitation series showed significant correlations with precipitation reconstructions from Mt. Xinglong, Mt. Helan, Ningwu and eastern China, suggesting that these five rainfall curves represent the general precipitation variations in the western-central environmentally sensitive zone of northern China. The calculations of the CRU grid points also indicate the existence of significant spatial correlation among these sites. Periodicity analysis showed clear 23.33-, 8.24-, 2.64- and 2.59-year cycles at a 99% confidence level for the reconstructed series during the past 155 years.</p

Tree-ring-based precipitation reconstruction for Mt. Xinglong, China, since AD 1679

On the basis of a significant correlation between the ring width of Qinghai spruce (Picea crassifolia Kom.) trees at Mt. Xinglong in north-central China and observed instrumental data, a transfer function was designed and the annual precipitation (from the previous July to the current June) was reconstructed for a period spanning 1679-2008 AD with an explained variance of 53.1% (1955-2008 AD). Intervals with precipitation more than the 330-year average occurred in 1686-1715, 1727-1741, 1774-1810 and 1871-1923. The intervals 1716-1726, 1740-1773, 1811-1870, 1924-1937 and 1980-2003 had precipitation lower than the 330-year average. Most drought events recorded in historical documents were captured by the reconstruction. Moreover, the reconstruction agreed well with tree-ring-based precipitation at Mt. Helan 400 km northeast of Mt. Xinglong. The results showed that the variability of the East Asian summer monsoon-related precipitation was synchronously at a large spatial and temporal scale within the environmentally sensitive region in northern China. The reconstruction was tested for periodicities by power spectrum analysis. The results showed remarkable 160-, 106.67-, 80-, 22.86-, 6.27- and 2- to 3-year cycles at a 99% confidence level for the past 330 years.</p

Tree-ring based PDSI reconstruction since 1853 AD in the source of the Fenhe river basin, Shanxi province, China

A robust tree-ring-width chronology was developed from two Pinus tabulaeformis sampling sites in the source of the Fenhe River, Shanxi Province, China. Based on the tree-ring-width indices, a 157-year long Palmer Drought Severity Index (PDSI) was reconstructed, which explains 53.7% of the variance of the modeled PDSI over the common period 1957-2008. The drought periods in the study area include 1914-1931 and 1970 to the present, whereas the wet periods were 1866-1892 and 1932-1969. The drought of 1914-1931 was a severe long-lasting drought with a low inter-annual variability, and the drought of 1970-2009 was an overall long-term drought with a high inter-annual variability. The period of 1866-1892 is a continuously wet period with a low inter-annual variability and the period of 1932-1969 is an overall long-term wet period with a high inter-annual variability. The reconstructed PDSI series in the source of the Fenhe River shows synchronous variations with the regional drought/wetness indices. Spatial correlation analyses indicate that the higher correlations lie exclusively in the Fenhe River Basin. This indicates that the reconstructed PDSI has regional representativeness and can represent the drought history of the entire Fenhe River Basin to some extent. Furthermore, the reconstructed PDSI matches with the variability of the per unit yield of summer grain crops in Shanxi Province very well and they have significant correlation. From a long-term perspective the reconstructed PDSI series could supply scientific and valuable information to the water resources management and then help the sustainable development in agricultural production, economic development, and ecosystem balance.</p

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.</p

Tree-Ring Based May-July Temperature Reconstruction Since AD 1630 on the Western Loess Plateau, China

Tree-ring samples from Chinese Pine (Pinus tabulaeformis Carr.) collected at Mt. Shimen on the western Loess Plateau, China, were used to reconstruct the mean May-July temperature during AD 1630-2011. The regression model explained 48% of the adjusted variance in the instrumentally observed mean May-July temperature. The reconstruction revealed significant temperature variations at interannual to decadal scales. Cool periods observed in the reconstruction coincided with reduced solar activities. The reconstructed temperature matched well with two other tree-ring based temperature reconstructions conducted on the northern slope of the Qinling Mountains (on the southern margin of the Loess Plateau of China) for both annual and decadal scales. In addition, this study agreed well with several series derived from different proxies. This reconstruction improves upon the sparse network of high-resolution paleoclimatic records for the western Loess Plateau, China.</p

Tree-ring based runoff reconstruction of the upper Fenhe River basin, NorthChina, since 1799 AD

To acquire long-term perspectives on the history of droughts, we have presented the first runoff reconstruction from March to July in the upper Fenhe River basin, based on Pinus tabulaeformis tree-ring width indices from the Guancen Mountains, headstream of the Fenhe River, North China. The reconstruction explains 54.8% of the instrumental runoff variance over the period from 1952 to 2008. An analysis of interannual runoff variability indicated that AD 2001 was not only the driest year for the instrumental period, but also the driest year since AD 1799 in the upper Fenhe River. More extreme single-year droughts existed in the 20th century than in the 19th century in the region. Multiyear and decadal scale dry regime analyses demonstrated that the instrumental runoff underestimated the potential severe and prolonged droughts in the Fenhe River basin in future, such as droughts similar to the multiyear pre-instrumental droughts from 1831 to 1842 and 1919 to 1929. Comparisons between the Fenhe River runoff reconstruction and other nearby precipitation reconstructions showed that drought occurrence has been synchronous in parts of north and northwestern China to some extent for the last 211 years. Spatial correlation analyses between runoff data and the gridded Palmer Drought Severity Index dataset indicated that the average runoff reconstruction from March to July in the upper Fenhe River represents the regional moisture variations in North China, especially in the entire Fenhe River basin. As for the highest frequency and severity of spring drought in Shanxi province, the runoff reconstruction can provide base data for historical drought analysis and water resource planning and management in the Fenhe River basin or even to entire Shanxi province.</p