Regional difference of the start time of the recent warming in Eastern China: prompted by a 165-year temperature record deduced from tree rings in the Dabie Mountains

Tree-ring studies from tropical to subtropical regions are rarer than that from extratropical regions, which greatly limit our understanding of some critical climate change issues. Based on the tree-ring-width chronology of samples collected from the Dabie Mountains, we reconstructed the April-June mean temperature for this region with an explained variance of 46.8%. Five cold (1861-1869, 1889-1899, 1913-1920, 1936-1942 and 1952-1990) and three warm (1870-1888, 1922-1934 and 2000-2005) periods were identified in the reconstruction. The reconstruction not only agreed well with the instrumental records in and around the study area, but also showed good resemblance to previous temperature reconstructions from nearby regions, indicating its spatial and temporal representativeness of the temperature variation in the central part of eastern China. Although no secular warming trend was found, the warming trend since 1970 was unambiguous in the Dabie Mountains (0.064 A degrees C/year). Further temperature comparison indicated that the start time of the recent warming in eastern China was regional different. It delayed gradually from north to south, starting at least around 1940 AD in the north part, around 1970 AD in the central part and around 1980s in the south part. This work enriches the high-resolution temperature reconstructions in eastern China. We expect that climate warming in the future would promote the radial growth of alpine Pinus taiwanensis in the subtropical areas of China, therefore promote the carbon capture and carbon storage in the Pinus taiwanensis forest. It also helps to clarify the regional characteristic of recent warming in eastern China.</p

Effects of non-linear temperature and precipitation trends on LoessPlateau droughts

In this study, we analysed the effects of non-linear temperature and precipitation trends on Loess Plateau droughts over the period of 1961e2010. The most commonly used drought index, the Palmer Drought Severity Index (PDSI), was used to represent the drought conditions in the study region. We first calculated the Loess Plateau PDSI using monthly temperature and precipitation from 53 meteorological stations and then determined trends in the PDSI, temperature, and precipitation using the ensemble empirical mode decomposition (EEMD) time series analysis method. Because of the different change characteristics and trends, precipitation plays an important role in the interannual variation in the PDSI, while temperature drives the PDSI trend change. The differences between the observed PDSI and the calculated results using the detrended temperature and observed precipitation, the observed temperature and detrended precipitation, and the detrended temperature and precipitation indicate that impact of the precipitation trend on droughts is smaller than the impact of the temperature trend. The increase in the observed temperature and limited decrease in the precipitation tend to increase drought in the Loess Plateau. The Loess Plateau will become drier and warmer in the future under climate change.</p

A Picea crassifolia Tree-Ring Width-BasedTemperature Reconstruction for the Mt.Dongda Region, Northwest China, and ItsRelationship to Large-Scale Climate Forcing

The historical May-October mean temperature since 1831 was reconstructed based on tree-ring width of Qinghai spruce (Picea crassifolia Kom.) collected on Mt. Dongda, North of the Hexi Corridor in Northwest China. The regression model explained 46.6% of the variance of the instrumentally observed temperature. The cold periods in the reconstruction were 1831-1889, 1894-1901, 1908-1934 and 1950-1952, and the warm periods were 1890-1893, 1902-1907, 1935-1949 and 1953-2011. During the instrumental period (1951-2011), an obvious warming trend appeared in the last twenty years. The reconstruction displayed similar patterns to a temperature reconstruction from the east-central Tibetan Plateau at the inter-decadal timescale, indicating that the temperature reconstruction in this study was a reliable proxy for Northwest China. It was also found that the reconstruction series had good consistency with the Northern Hemisphere temperature at a decadal timescale. Multi-taper method spectral analysis detected some low- and high-frequency cycles (2.3-2.4-year, 2.8-year, 3.4-3.6-year, 5.0-year, 9.9-year and 27.0-year). Combining these cycles, the relationship of the low-frequency change with the Pacific Decadal Oscillation (PDO), North Atlantic Oscillation (NAO) and Southern Oscillation (SO) suggested that the reconstructed temperature variations may be related to large-scale atmospheric-oceanic variations. Major volcanic eruptions were partly reflected in the reconstructed temperatures after high-pass filtering; these events promoted anomalous cooling in this region. The results of this study not only provide new information for assessing the long-term temperature changes in the Hexi Corridor of Northwest China, but also further demonstrate the effects of large-scale atmospheric-oceanic circulation on climate change in Northwest China

Growing-season precipitation since 1872 in the coastal area of subtropicalsoutheast China reconstructed from tree rings and its relationship with theEast Asian summer monsoon system

Tree rings from temperate zones of the world have provided abundant palaeo- ecological and paleo-hydroclimatic information. However, tree rings from subtropical to tropical regions remain relatively scarce, which greatly limit our fully understanding about the climate change issues. In the present work, tree-ring-width (TRW) measurements of Masson pine from Fujian province, the coastal area of subtropical southeast China were successfully crossdated and a TRW STD chronology was developed from 1854 to 2012. Significantly positive correlation was identified between the tree rings and April&ndash;November total precipitation (r&nbsp;=&nbsp;0.71, p&nbsp;&lt;&nbsp;0.01). The reconstructed April&ndash;November precipitation exhibited two comparatively wet (1876&ndash;1886 and 1957&ndash;1962) and one comparatively dry (1986&ndash;2004) periods. An evident drying trend since 1959 was seen and it was mitigated after 1993. Most of the extreme low-precipitation years in the reconstruction were supported by the historical records. As revealed by the spatial correlation patterns, our precipitation reconstruction was also consistent with other hydroclimatic records along the coastal areas of southeast China, proving its ability to capture the large-scale hydrological signal in southeast China (mainly refers to the south of the middle-lower reaches of Yangtze River). The reconstructed precipitation showed significant correlation with the East Asian summer Monsoon (EASM) index. Moreover, it also indicated simultaneous variation with the monsoon precipitation in North China on a decadal scale, implying that growing season precipitation variations in both regions were influenced by the EASM strength. This work highlights the potential of using tree-ring width to reconstruct precipitation in subtropical southeast China, while the relevant issues about precipitation variation in this region is far from resolved

Tree-ring d18O, a tool to crack the paleo-hydroclimatic code insubtropical China

Tree ring plays an important role in deciphering the paleoclimatic signals. Although tree-ring width (TRW) has obvious advantages in studying the hydroclimatic history in the middle-high latitudes, it has certain limitation in hydroclimatic signal extraction in the tropical to subtropical areas, which greatly limits our fully understanding about the hydroclimatic history in these areas. In this work, tree-ring &delta;18O (&delta;18Otree) records from five independent tree-ring cores were measured and a composite &delta;18Otree record (1939&ndash;2014) was developed in Guilin, subtropical southwest China. No &ldquo;juvenile effect&rdquo; existed in this &delta;18Otree record and no relationship was found between &delta;18Otree and TRW. Correlation analysis with the climatic parameters demonstrated that the &delta;18Otree record significantly (p&nbsp;&lt;&nbsp;0.01) and negatively correlated with all the hydroclimatic parameters during the growing season (e.g. April&ndash;October precipitation, August&ndash;October relative humidity and April&ndash;November standardized precipitation&ndash;evapotranspiration index), while it only positively correlated with the August&ndash;September mean temperature (p&nbsp;&lt;&nbsp;0.05). At high frequency, the above relationships were greatly strengthened. Compared with the temperature-limited TRW in Guilin and other areas of subtropical China, &delta;18Otree was a better choice for hydroclimatic reconstruction. Moreover, the &delta;18Otree record in Guilin showed high consistency with other moisture-sensitive &delta;18Otree records in a large area of central-southeastern China. Analysis revealed that both large-scale circulation system (e.g. Indian summer monsoon, ENSO, westerlies) and local weather system significantly influenced the growing-season hydroclimatic variation in the study area. This study provides great potential for extracting hydroclimatic information from longer-living trees in subtropical China