Shao Xuemei

Tree-ring based PDSI reconstruction since AD 1842 in the ortindag sand land, east inner mongolia

Based on three Chinese pine (Pinus tabulaeformis Carr.) and one Meyer spruce (Picea meyeri Rehd. et Wils.) ring-width chronologies, a 163-year drought history was reconstructed in the eastern Ortindag Sand Land. All tree-ring chronologies show large inter-annual variations and strong common signals and fairly consistent variation between different chronologies, indicating that they are excellent proxy of regional climate. A regional chronology (RC) was established by averaging the four standard chronologies and further employed for the analysis and climatic reconstruction. The analysis revealed that tree growth is primarily limited by low precipitation in February–March and June–July and high temperature in May–July. In addition, RC has high correlations with the monthly Palmer drought severity index (PDSI) prior to and during the growing season because the PDSI considers the accumulation of the droughts. Response function analysis revealed that RC only exhibits significant correlations with the PDSI in June and July (close to the 95% significance level in May). Because May–July is a critical period for tree growth, the average May–July PDSI (PDSI5–7) was reconstructed back to 1842 using RC in the Ortindag Sand Land. The reconstruction can explain 52% of the PDSI variance and the equation was rather stable over time. It agrees well with the variation of the average dryness/wetness indices in North China, and captures the decline process of the East Asian summer monsoon since the mid-1960s. It is worth noting that the Ortindag Sand Land has experienced the most severe drought in the recent 40 years based on the 163-year drought reconstruction. Like summer precipitation in North China the reconstructed PDSI5–7 also displays a 20-year oscillation.

Ecosystem vulnerability of China under B2 climate scenario in the 21st century

This paper applies climate change scenarios in China based on the SRES assumptions with the help of RCMs projections by PRECIS (providing regional climates for impacts studies) system introduced to China from the Hadley Centre for Climate Prediction and Research at a high-resolution (50 km×50 km) over China. This research focuses on B2 scenario of SRES. A biogeochemical model “Atmosphere Vegetation Integrated Model (AVIM2)” was applied to simulating ecosystem status in the 21st century. Then vulnerability of ecosystems was assessed based on a set of index of mainly net primary production (NPP) of vegetation. Results show that climate change would affect ecosystem of China severely and there would be a worse trend with the lapse of time. The regions where having vulnerable ecological background would have heavier impacts while some regions with better ecological background would also receive serious impacts. Extreme climate even would bring about worse impact on the ecosystems. Open shrub and desert steppe would be the two most affected types. When the extreme events happen, vulnerable ecosystem would extend to part of defoliate broad-leaved forest, woody grassland and evergreen conifer forest. Climate change would not always be negative. It could be of some benefit to cold region during the near-term. However, in view of mid-term to long-term negative impact on ecosystem vulnerability would be enormously.

Annual temperature recorded in tree-ring from Songpan region

Three tree-ring STD chronologies of Abies faxoniana were developed from Songpan region Sichuan Province, and a regional chronology(RC) was established based on the three STD chronologies. The calculation shows that the tree-ring width was significantly correlated with temperature, and the RC had the highest correlation( r =0.576, P R adj2=32%, N =59, F =28.33). In the past 310 years, there were 8 warm periods and 7 cool periods. According to analysis of temporal and spatial correlation, it indicated that the reconstructed series with good spatial and temporal representation. Our reconstruction was validated by other tree-ring based temperature reconstructions from the surrounding area, glacier advances and retreats, and the documented climate disaster events. MTM analysis shows that there exist periods of 2-3 a, 26 a, quasi-33 a and quasi-40 a cycles.

Precipitation change over the past 1000 years recorded in Sabina Tibetica Tree Rings in Lake Qinghai Basin

Tree-ring width chronologies of Sabina Tibetica were constructed based on tree-rings of 1061-year sampled in Tianjun county of Lake Qinghai Basin. The response function analysis showed that the chronologies were sensitive to the annual precipitation so that the paper reconstructed annual precipitation series. The cross-validation method was used to check in the stability of the calibration equation, and the result indicated that the equation was stable and the variation of reconstructed annual precipitation was dependable and representative. There were six years showing precipitation below normal stage, which were periods of 1001 to 1060, 1131 to 1320, 1411 to 1510, 1691 to 1740, 1811 to 1850 and 1911 to 1940. There were seven years that showed precipitation above normal stage, which were period of 961 to 1000, 1061 to 1110, 1321 to 1410, 1511 to 1650, 1741 to 1790, 1881 to 1910 and 1941 to 2000. The occurrence of abrupt precipitation was once a time every 53 years.Reconstructed precipitation series showed an unstable period from the 13th to 14th centuries, but stable periods in the 12th, 17th and 20th centuries.