老哈河流域不同气候区间天然植被的实际蒸散发量研究

本文基于PM公式,结合LAI数据,考虑冠层截留雨水的蒸发量,针对老哈河流域不同气候区条件,对天然植被进行了实际蒸散发量的测算.比较了在不同气候区条件下,天然植被蒸散发量的差异.结果表明:老哈河流域天然林地的实际蒸散发量明显要大于天然草地的实际蒸散发量.考虑土壤水分条件下,流域内不同气候区间的实际蒸散发量差异并不大,其中土壤水分含量是影响天然植被实际蒸散发量的重要因素.老哈河流域天然草地普遍存在土壤水分胁迫现象,需要在缺水时段,对天然植被进行人工补水,从而维持生态系统的稳定.

基于孢粉植物类群气候区间的古气候定量重建方法

目前一些较高精度的孢粉定量气候重建手段往往难以直接运用到较古老的新近纪甚至早-中第四纪地层的孢粉分析中。近十多年来,共存因子法在新近纪古气候研究中广泛应用,但该方法用于孢粉数据的定量气候转换时仍存在较大误差。本文详细论述了共存因子法的基本原理,并介绍了另一种定量古气候重建方法——孢粉气候区间法。该方法考虑到孢粉含量的意义,具有较高的气候重建精度和捕捉较小幅度气候变化信息的潜力。为比较共存因子法和气候区间法在孢粉-气候定量恢复研究中的精确度,本文同时用两种方法对琼州海峡CZ-XXZT-06钻孔6个不同深度的样品分别进行年均温定量重建,结果显示气候区间法优于共存因子法。然而,上述两种方法都依赖于现代植物类群或孢粉种类与气候的关系。区域植物分布调查数据和现代孢粉谱的数量及样点覆盖范围最终决定上述两种方法气候重建精度。

基于孢粉植物类群气候区间的全新世东北地区气候变化

通过数字化东北地区内七个样点剖面(包括赤池、同江、月亮湖、四海龙湾、柳河哈尼湖、麦里和霍拉剖面)的孢粉百分含量数据,截取东亚孢粉数据库资料中部分科属花粉的百分含量对应的年均温和年均降水量区间,利用气候区间法重建剖面多个数据点的年均温与年降水量.得出距今0~3000 a,七个样点中以霍拉剖面为代表的大兴安岭北部年均温最低,温度范围为-5.3℃^-1.1℃,长白山区柳河哈尼湖年均温最高,温度范围为-4.1℃~13℃;降水量最低为辽西地区的麦里剖面,年均降水量为100 mm左右,柳河哈尼湖剖面降水量较其他样点较充沛,年均降水量在960~620 mm之间.偏东部的长白山地区对季风的响应相比季风/非季风过渡带早1000 a左右.

一种新的集合预报权重平均方法

提出了一种新的考虑权重的集合预报成员平均方法。使用气候等概率区间来对集合成员进行分组,并根据气候等概率区间的大小及其中的成员数,对集合成员的权重进行调整,得到了一种改进的集合平均预报结果。检验表明,它可以进一步提高集合平均预报的效果。相对于提高模式分辨率或发展庞大的集合预报系统,这种方法的效果是显著的。

Drought over China in the 21st Century: Results of RegCM3

Based on 150-year simulations of a regional climate model, RegCM3, under the Special Report on Emissions Scenarios (SRES) A1B scenario, the effective drought index (EDI) is used to project the future drought change in China. During the baseline period 1986-2005, RegCM3 was found to reliably simulate the spatial pattern of drought over the country. Over the 21st century, the regionally averaged EDI should increase, corresponding to a decrease of drought, while the probability of extreme drought events should increase. Geographically, drought should clearly increase in Northeast China, the middle and lower reaches of the Yangtze River valley, Southwest China, and southern Tibet but decrease in most parts of the rest of the country.

Variation of Floods Characteristics and Their Responses to Climate and Human Activities in Poyang Lake, China

The Poyang Lake is one of the most frequently flooded areas in China. Understanding the changing characteristics of floods as well as the affecting factors is an important prerequisite of flood disaster prevention and mitigation. The present study identified the characteristics variations of historical floods in the Poyang Lake and their tendencies based on the Mann-Kendall(M-K) test, and also investigated the related affecting factors, both from climate and human activities. The results revealed that the highest flood stages, duration as well as hazard coefficient of floods showed a long-term increasing linear trend during the last 60 years with the M-K statistic of 1.49, 1.60 and 1.50, respectively. And, a slightly increasing linear trend in the timing of the highest stages indicated the floods occurred later and later during the last six decades. The rainfall during the flood season and subsequent discharges of the Changjiang(Yangtze) River and runoff from the Poyang Lake Basin were mainly responsible for the severe flood situation in the Poyang Lake in the 1990 s. In addition, the intensive human activities, including land reclamation and levee construction, also played a supplementary role in increasing severity of major floods. While, the fewer floods in the Poyang Lake after 2000 can be attributed to not only the less rainfall over the Poyang Lake Basin and low discharges of the Changjiang River during flood periods, but also the stronger influences of human activity which increased the floodwater storage of the Poyang Lake than before.

Impact of Different East Asian Summer Monsoon Circulations on Aerosol-Induced Climatic Effects

The different spatial distributions of aerosol-induced direct radiative forcing and climatic effects in a weak （2003） and a strong （2006） East Asian summer monsoon （EASM） circulation were simulated using a high-resolution regional climate model （RegCM3）.Results showed that the atmospheric circulations of summer monsoon have direct relations with transport of aerosols and their climatic effects.Both the top-of-the-atmosphere （TOA） and the surface-negative radiative forcing of aerosols were stronger in weak EASM circulations.The main difference in aerosol-induced negative forcing in two summers varied between 2 and 14 W m-2 from the Sichuan Basin to North China,where a maximum in aerosol-induced negative forcing was also noticed in the EASM-dominated areas.The spatial difference in the simulated aerosol optical depth （AOD） in two summers generally showed the similar pictures.Surface cooling effects induced by aerosols were spatially more uniform in weak EASM circulations and cooler by about 1-4.5℃.A preliminary analysis here indicated that a weaker low-level wind speed not conducive to the transport and diffusion of aerosols could make more contributions to the differences in the two circulations.

Uncertainty in crossing time of 2 °C warming threshold over China

The 2 ℃ warming target has been used widely in global and regional climate change research. Previous studies have shown large uncertainties in the time when surface air temperature （SAT） change over China will reach 2℃ rela- tive to the pre-industrial era. To understand the uncertainties, we analyzed the projected SAT in the twenty-first century using 40 state-of-the-art climate models under two Repre- sentative Concentration Pathways （RCP4.5 and RCPS.5） from the Coupled Model Intercomparison Project Phase 5. The 2℃ threshold-crossing time （TCT） of SAT averaged across China was around 2033 and 2029 for RCP4.5 and RCP8.5, respectively. Considering a 4-1o- range of inter- model SAT change, the upper and lower bounds of the 2 ℃ TCT could differ by about 25 years or even more. Uncer- tainty in the projected SAT and the warming rate around the TCT are the two main factors responsible for the TCT uncertainty. The former is determined by the climate sensi- tivity represented by the global mean surface temperature response. About 45 % of the intermodel variance of the projected 2 ~C TCT for averaged SAT over China can be explained by climate sensitivity across the models, which is contributed mainly by central and southern China. In a cli- mate more sensitive to CO2 forcing, stronger greenhouse effect, less stratus cloud over the East Asian monsoon region, and less snow cover on the Tibetan Plateau result in increased downward longwave radiation, increased shortwave radia- tion, and decreased shortwave radiation reflected by the surface, respectively, all of which may advance the TCT.

Uncertainty and Sensitivity Analyses for Modeling Long-Term Soil Organic Carbon Dynamics of Paddy Soils Under Different Climate-Soil-Management Combinations

Reporting modeling results with uncertainty information can benefit decision making by decreasing the extent that variability exerts a disproportionate influence on the options selected. For making decisions with more confidence, the uncertainty interval should be as narrow as possible. Here, the soil organic carbon （SOC） dynamics of the major paddy soil subgroup from 4 different paddy field regions of China （located in 4 counties under different climate-soil-management combinations） were modeled using the DeNitrification- DeComposition （DNDC） model for the period from 1980 to 2008. Uncertainty intervals associated with the SOC dynamics for these 4 subgroups were estimated by a long-term global sensitivity and uncertainty analysis （i. e., the Sobolt method）, and their sensitivities to 7 influential factors were quantified using the total effect sensitivity index. The results, modeled with high confidence, indicated that in the past 29 years, the studied paddy soils in Xinxing, Yixing, and Zhongjiang counties were carbon （C） sinks, while the paddy soil in Helong County was a C source. The 3 C sinks sequestered 12.2 （5.4, 19.6）, 17.1 （8.9, 25.0）, and 16.9 （-1.2, 33.6） t C ha-1 （values in the parentheses are the 5th and 95th percentiles, respectively）. Conversely, the C source had a loss of -5.4 （-14.2, 0.06） t C ha-1 in the past 29 years. The 7 factors, which changed with the climate-soil-management context, exhibited variable influences on modeled SOC. Measures with potential to conserve or sequestrate more C into paddy soils, such as incorporating more crop residues into soils and reducing chemical fertilizer application rates, were recommended for specific soils based on the sensitivity analysis results.

Rates of temperature change in China during the past 2000 years

Using 24 proxy temperature series, the rates of temperature change in China are analyzed at the 30- to 100-year scales for the past 2000 years and at the 10-year scale for the past 500 years. The results show that, at the 100-year scale, the warming rate for the whole of China in the 20th century was only 0.6±1.6℃/100 a （interval at the 95% confidence level, which is used here- after）, while the peak warming rate for the period from the Little Ice Age （LIA） to the 20th century reached 1.1_＋1.2~C/100 a, which was the greatest in the past 500 years and probably the past 2000 years. At the 30-year scale, warming in the 20th century was quite notable, but the peak rate was still less than rates for previous periods, such as the rapid warming from the LIA to the 20th century and from the 270s-290s to 300s-320s. At the 10-year scale, the warming in the late 20th century was very evident, but it might not be unusual in the context of warming over the past 500 years. The exact timing, duration and magnitude of the warming peaks varied from region to region at all scales. The peak rates of the 100-year scale warming in the AD 180s-350s in northeastern China as well as those in the 260s-410s and 500s-660s in Tibet were all greater than those from the mid-19th to 20th century. Meanwhile, the rates of the most rapid cooling at scales of 30 to 100 years in the LIA were promi-nent, but they were also not unprecedented in the last 2000 years. At the 10-year scale, for the whole of China, the most rapid decadal cooling in the 20th century was from the 1940s to 1950s with a rate of -0.3±0.6℃/10 a, which was similar to rates for periods before the 20th century. For all regions, the rates of most rapid cooling in the 20th century were all less than those for previous periods.