Climate change and social vicissitudes in China over the past two millennia

The relation between climate change and historical rhythms has long been discussed. However, this type of study still faces the lack of high-resolution data concerning long-term socio-economic processes. In this study, we collected 1586 items of direct and proffered evidence from 29 Chinese history books. We used semantic analysis to reconstruct a quantitative series of the social vicissitudes of the past 2000 yr with a 10-yr resolution to express the phase transition of the social vicissitudes of the dynasties in China. Our reconstruction demonstrates that social vicissitudes have clear cyclical features on multiple time scales. Analysis of the association of social rise and fall with climate change indicates that temperature displayed more significant effects on social vicissitudes in the long term, while precipitation displayed more significant effects on the social vicissitudes in the short term. There are great overlaps between social and climatic variables around the predominant or periodic bands. Social rise mostly occurred in the centennial-scale warm periods, whereas social decline mostly occurred in the centennial-scale cold periods. Under warm-wet conditions, social rise occurred over 57% of the time; under cold-dry conditions, the social decline occurred over 66% of the time. (C) 2016 University of Washington. Published by Elsevier Inc. All rights reserved

Analysing the uncertainty of estimating forest carbon stocks in China

Earth surface systems are controlled by a combination of global and local factors, which cannot be understood without accounting for both the local and global components. The system dynamics cannot be recovered from the global or local controls alone. Ground forest inventory is able to accurately estimate forest carbon stocks in sample plots, but these sample plots are too sparse to support the spatial simulation of carbon stocks with required accuracy. Satellite observation is an important source of global information for the simulation of carbon stocks. Satellite remote sensing can supply spatially continuous information about the surface of forest carbon stocks, which is impossible from ground-based investigations, but their description has considerable uncertainty. In this paper, we validated the Kriging method for spatial interpolation of ground sample plots and a satellite-observation-based approach as well as an approach for fusing the ground sample plots with satellite observations. The validation results indicated that the data fusion approach reduced the uncertainty of estimating carbon stocks. The data fusion had the lowest uncertainty by using an existing method for high-accuracy surface modelling to fuse the ground sample plots with the satellite observations (HASM-S). The estimates produced with HASM-S were 26.1 and 28.4% more accurate than the satellite-based approach and spatial interpolation of the sample plots respectively. Forest carbon stocks of 7.08 Pg were estimated for China during the period from 2004 to 2008, an increase of 2.24 Pg from 1984 to 2008, using the preferred HASM-S method

Contribution of environmental variability and ecosystem functional changes to interannual variability of carbon and water fluxes in a subtropical coniferous plantation

Accurate quantification of the contribution of environmental variability and functional changes to the interannual variability of net ecosystem production (NEP) and evapotranspiration (ET) in coniferous forests is needed to understand global carbon and water cycling. This study quantified these contributions to the interannual variability of NEP and ET for a subtropical coniferous plantation in southeastern China, and the effect of drought stress on these contributions was also investigated. NEP and ET were derived from eddy covariance measurements carried out over the period 2003-2012. A homogeneity-of-slopes model was adopted to quantify the contribution to the interannual variability of these fluxes. Environmental variability accounted for 71% and 85.7% of the interannual variability of NEP and ET, respectively; however, functional changes accounted for only 11.3% and 5.9%, respectively. Furthermore, functional changes explained more of the interannual variability of NEP in dry years (16.3%) than in wet years (3.8%), but there was no obvious change in the contribution of functional changes to the interannual variability of ET in dry (4.7%) or wet (5.5%) years. Thus, environmental variability rather than ecosystem functional changes dominated the interannual variability of both ET and NEP. However, different environmental variables controlled the interannual variability of NEP and ET. The results also indicated that, compared with NEP, ET was more resistant to drought stress through the self-regulating mechanisms of this plantation

Evaluation of the Community Land Model simulated carbon and water fluxes against observations over ChinaFLUX sites

The Community Land Model (CLM) is an advanced process-based land surface model that simulates carbon, nitrogen, water vapor and energy exchanges between terrestrial ecosystems and the atmosphere at various spatial and temporal scales. We use observed carbon and water fluxes from five representative Chinese Terrestrial Ecosystem Flux Research Network (ChinaFLUX) eddy covariance tower sites to systematically evaluate the new version CLM4.5 and old version CLM4.0, and to generate insights that may inform future model developments. CLM4.5 underestimates the annual carbon sink at three forest sites and one alpine grassland site but overestimates the carbon sink of a semi-arid grassland site. The annual carbon sink underestimation for the deciduous-dominated forest site results from underestimated daytime carbon sequestration during summer and overestimated nighttime carbon emission during spring and autumn. Compared to CLM4.0, the bias of annual gross primary production (GPP) is reduced by 24% and 28% in CLM4.5 at two subtropical forest sites. However, CLM4.5 still presents a large positive bias in annual GPP. The improvement in net ecosystem exchange (NEE) is limited, although soil respiration bias decreases by 16%-43% at three forest sites. CLM4.5 simulates lower soil water content in the dry season than CLM4.0 at two grassland sites. Drier soils produce a significant drop in the leaf area index and in GPP and an increase in respiration for CLM4.5. The new fire parameterization approach in CLM4.5 causes excessive burning at the Changbaishan forest site, resulting in an unexpected underestimation of NEE, vegetation carbon, and soil organic carbon by 46%, 95%, and 87%, respectively. Overall, our study reveals significant improvements achieved by CLM4.5 compared to CLM4.0, and suggests further developments on the parameterization of seasonal GPP and respiration, which will require a more effective representation of seasonal water conditions and the partitioning of net radiation between sensible and heat fluxes. (C) 2016 Elsevier B.V. All rights reserved

Using glacier area ratio to quantify effects of melt water on runoff

Twenty-four headwater catchments with varying glacier area ratios (GARs) in the Eastern and Central Tian Shan Mountains were simulated by the glacier-enhanced Soil and Water Assessment Tool (SWAT) model from 1961 to 2007. The mean catchment GAR ranges between 0.7% and 44.8% with a mean of 8.6%. Through synthetic analysis of the glacio-hydrological processes simulation results of the catchments, it was found that the GAR is an effective index that can be used to interpret quantitatively the varying influences of glaciers on runoff across catchments. Among the twenty-four catchments, the ratio of glacier melt contribution (RGMC) to runoff varies between 3.5% and 67.5% with a mean of 24.0%; the ratio of ice melt contribution (RIMC) between 1.4% and 35.8% with a mean of 10.5%; the ratio of ice melt in glacier melt between 33.4% and 59.1% with a mean of 43.4%; the runoff coefficient (RC) between 0.24 and 0.90 with a mean of 0.52; and the coefficient of variation (CV) of runoff between 0.10 and 0.29 with a mean of 0.18. Based on synthetic analysis, it was found that (1) power functions fit the relations between RGMC, RIMC, RC, and CV and GAR with high certainty; (2) the CV decreases with increasing GAR while others increase; and (3) these power functions change sensitively with GAR when GAR is less than 10%, implicating that a small change in GAR may cause remarkable changes in RGMC, RIMC, RC, and CV in the less glacierized catchments. (C) 2016 Published by Elsevier B.V

Statistical study to identify the key factors governing ground water recharge in the watersheds of the arid Central Asia

Understanding the source and recharge of ground waters is of great significance to our knowledge in hydrological cycles in arid environments over the world. Northern Xinjiang in northwestern China is a significant repository of information relating to the hydrological evolution and climatic changes in central Asia. In this study, two multivariate statistical techniques, hierarchical cluster analysis (HCA) and principal component analysis (PCA), were used to assess the ground water recharge and its governing factors, with the principal idea of exploring the above techniques to utilize all available hydrogeochemical variables in the quality assessment, which are not considered in the conventional techniques like Stiff and Piper diagrams. Q-mode HCA and R-mode PCA were combined to partition the water samples into seven major water clusters (C1-C7) and three principal components (PC1-PC3, PC1 salinity, PC2 hydroclimate, PC3 contaminant). The water samples C1+C4 were classified as recharge area waters (Ca-HCO3 water), C2+C3 as transitional zone waters (Ca-Mg-HCO3-SO4 water), and C5+C6+C7 as discharge area waters (Na-SO4 water). Based on the Q-mode PCA scores, three groups of geochemical processes influencing recharge regimes were identified: geogenic (i.e., caused by natural geochemical processes), geomorphoclimatic (caused by topography and climate), and anthropogenic (caused by ground water contamination). It is proposed that differences in recharge mechanism and ground water evolution, and possible bedrock composition difference, are responsible for the chemical genesis of these waters. These will continue to influence the geochemistry of the northern Xinjiang drainage system for a long time due to its steady tectonics and arid climate. This study proved that the chemistry differentiation of ground water can effectively support the identification of ground water recharge and evolution patterns

基于CO2FIX模型的华北落叶松人工林碳循环过程

为了探明华北落叶松(Larix gmelinii var.principis-rupprechtii)人工林的碳循环过程,该研究以河北围场地区的华北落叶松人工林为例,基于CO2FIX模型,以在当地的实际调查数据、文献数据作为输入数据,从生物量、土壤和木质林产品碳库3个方面探讨了华北落叶松人工林的碳循环过程和碳汇能力。结果表明:华北落叶松人工林土壤碳库最大,生物量碳库次之,林产品碳库最小,但是林产品碳库随时间呈逐渐增加的趋势;在一个轮伐期内(50年),每公顷华北落叶松人工林约固定了250t碳,其中约70%通过凋落物和采伐剩余物的方式进入土壤碳库,约30%进入木质林产品碳库;华北落叶松人工林在生长的大部分时间是一个碳的吸收汇,而在森林采伐时成为暂时的排放源,从长时间尺度上看,每公顷华北落叶松人工林每年大约固定0.3 t左右的碳。该研究结果表明了木质林产品碳库在人工林碳循环中的重要作用,这将有助于更加全面地认识人工林的碳循环过程和碳汇能力