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

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 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

A wetness index derived from tree-rings in the Mt. Yishan area of China since 1755 AD and its agricultural implications

Dendroclimatological techniques were employed to investigate the relationship between Chinese Pinus (Pinus tabulaeformis Carr.) growth and climatic variability in the Mt. Yishan region of Shandong Province, China, over the past 253 years. Using regression analysis, the wetness index (WI) was reconstructed for the Mt. Yishan area for the period 1755-2007 AD based on tree-ring widths; predictor variables accounted for 40 % of the variance. The reconstructed time-series displayed an increasing trend after the late 1960s. Both the estimated and the observed WI for May-August were better correlated with precipitation than temperature during the period 1958-2007 AD, indicating that the contribution of precipitation to the WI was larger than temperature in the study area. The reconstructed WI was compared with the dryness/wetness index of China and land areas that were affected by droughts and floods using the agricultural statistics for Shandong Province. In addition, the WI time-series corresponded well with the peanut yield in Shandong Province at high frequency, which may be reasonable in the context of agriculture in Shandong. The 3-, 5- to 6- and 9- to 10-year periodicities detected in the time-series suggested that the reconstructed WI in the Mt. Yishan area may be related to large-scale climate variations.</p

Amplitudes, rates, periodicities and causes of temperature variations in the past 2485 years and future trends over the central-eastern Tibetan Plateau

Amplitudes, rates, periodicities, causes and future trends of temperature variations based on tree rings for the past 2485 years on the central-eastern Tibetan Plateau were analyzed. The results showed that extreme climatic events on the Plateau, such as the Medieval Warm Period, Little Ice Age and 20th Century Warming appeared synchronously with those in other places worldwide. The largest amplitude and rate of temperature change occurred during the Eastern Jin Event (343-425 AD), and not in the late 20th century. There were significant cycles of 1324 a, 800 a, 199 a, 110 a and 2-3 a in the 2485-year temperature series. The 1324 a, 800 a, 199 a and 110 a cycles are associated with solar activity, which greatly affects the Earth surface temperature. The long-term trends (&gt;1000 a) of temperature were controlled by the millennium-scale cycle, and amplitudes were dominated by multi-century cycles. Moreover, cold intervals corresponded to sunspot minimums. The prediction indicated that the temperature will decrease in the future until to 2068 AD and then increase again.</p

Individual and pooled tree-ring stable-carbon isotope series in Chinese pine from the Nan Wutai region, China: Common signal and climate relationships

To investigate the differences in the climatic signals in stable-carbon isotopic composition captured by averaging series from individual trees versus raw wood of trees pooled prior to analysis, we analyzed two groups of Chinese pine (Pinus tabulaeformis Carr.) from the Nan Wutai region of the Qinling Mountains, China. One group included three trees that were analyzed separately, and the other group comprised four other trees that were pooled prior to preparation and analysis. All &delta;13C series were positively correlated (r = 0.50&ndash;0.58, p &lt; 0.0001) for the period AD 1901&ndash;2003. After removing the effects of changing &delta;13C of atmospheric CO2, correlations between the meteorological data and all individual and pooled discrimination (∆13C) series revealed significant negative responses to temperature for several specific months and for mean January to September (TJ&ndash;S) temperature. We used a &ldquo;numerical mix method&rdquo; (NMM, equivalent to unweighted mean), by averaging individual ∆13C series (NPS1+NPS2+NPS3), to generate a new series that more strongly correlated to climate series TJ&ndash;S (r = &minus; 0.67, p &lt; 0.0001). This time interval from January through September (J&ndash;S) includes the growing season and months prior to the growing season, but the temperature prior to the growing season may provide energy necessary for timely initiation of growth. Thus, the mean TJ&ndash;S is significant for plant growth and is consistent with the tree physiology in this region. Our results suggest that the numerical mix method with tree-ring stable isotope data from three trees provides a series quite satisfactory for climatic reconstruction. The relationship of the numerical mix model ∆13C with temperature was stronger than for the pooled series, suggesting numerical mixing of series can be more effective than raw wood sample pooling at least according to the trees in this study.</p

Reconstructed May-July mean maximum temperature since 1745 AD based on tree-ring width of Pinus tabulaeformis in Qianshan Mountain, China

A tree-ring-width chronology of Pinus tabulaeformis was developed from the Qianshan Mountain, Liaoning province, northeastern China. Based on the correlation between the ring width and instrumental data, a transfer function was designed and the May-July mean maximum temperature (MMT) from 1745 to 2012 was reconstructed. The reconstruction explains 42.7% of the instrumental variance during the calibration period (41.7% after adjusting for the loss of the degrees of freedom). The reconstructed MMT is similar to several observed MMT series and the temperature index in north-central China, which indicated that the decrease in summer temperatures in the 20th century was a large scale phenomenon. The reconstruction also showed that high MMT values corresponded to historical drought events in Liaoning. In addition, a spatial Correlation analyses revealed that the MMT reconstruction is regionally representative. Significant 128.2-, 64.1-, 18.6-, 3.46-, 3.19-, 2.43-, 2.15- and 2.10-year cycles were detected in the reconstructed MMT series from Qianshan Mountain.</p

Tree-ring stable carbon isotope-based May-July temperature reconstruction over Nanwutai, China, for the past century and its record of 20th century warming

Growth anomaly of trees in some regions was detected under current episode of rapid warming. This raises a dilemma for temperature reconstructions by using tree-ring width which is believed to be the most important proxy on inter-annual temperature reconstruction during the past millenniums. Here we employed the tree-ring &delta;13C to reconstruct temperature variations for exploring their potential on capturing signals of rapid warming, and to test how its difference with the tree-ring width based reconstruction. In this study the mean May-July temperature (TM-J) was reconstructed over the past century by tree-ring &delta;13C of Chinese pine trees growing in the Nanwutai region. The explained variance of the reconstruction was 43.3% (42.1% after adjusting the degrees of freedom). Compared to a ring-width temperature reconstruction (May-July) from the same site, the tree-ring &delta;13C-based temperature reconstruction offered two distinct advantages: 1) it captured a wider range of temperature variability, i.e., at least May-July, even over a longer part of the year, January-September; and 2) the reconstruction preserved more low-frequency climate information than that of ring width did.The 20th century warming was well represented in the Nanwutai tree-ring &delta;13C temperature reconstruction, which implied that stable carbon isotope of tree rings potentially represents temperature variations during historical episodes of rapid warming. A spatial correlation analysis showed that our temperature reconstruction represented climate variations over the entire Loess Plateau in north-central China. Significant positive correlations (p&lt;0.1) were found between the temperature reconstruction and ENSO, as well as SSTs in the Pacific and Indian Oceans. The reconstruction showed the periodicities of 22.78-, 4.16-, 3.45-3.97- and 2.04-2.83-year quasi-cycles at a 95% confidence level. Our results suggested that temperature variability in the Nanwutai region may be linked to Pacific and Indian Ocean SST variations and solar activity.</p