城市公共自行车自愿碳减排机制初探——以北京市为例

公共自行车系统是待开发的交通自愿碳减排项目。本文采用CCER方法学中的“快速公交项目”,计算北京市2012年公共自行车系统自愿碳减排量,并估算收益。结果显示：北京市2012年公共自行车自愿碳减排量为43.95 t CO₂,出售可获得1538元的收益。同时估算得到北京市2015年公共自行车碳减排量为6874.5 t CO₂,出售可获得约24万的收益。因此,北京等交通需求膨胀的特大型城市,随着公共自行车系统的持续壮大发展,公共自行车运营企业的经济效益有望通过碳交易实现较大提升空间。     

Numerical simulations of a highway bridge structure employing passive negative stiffness device for seismic protection

A new passive seismic response control device has been developed, fabricated, and tested by the authors and shown to be capable of producing negative stiffness via a purely mechanical mechanism, thus representing a new generation of seismic protection devices. Although the concept of negative stiffness may appear to be a reversal on the desired relationship between the force and displacement in structures (the desired relationship being that the product of restoring force and displacement is nonnegative), when implemented in parallel with a structure having positive stiffness, the combined system appears to have substantially reduced stiffness while remaining stable. Thus, there is an ‘apparent weakening and softening’ of the structure that results in reduced forces and increased displacements (where the weakening and softening is of a non‐damaging nature in that it occurs in a seismic protection device rather than within the structural framing system). Any excessive displacement response can then be limited by incorporating a damping device in parallel with the negative stiffness device. The combination of negative stiffness and passive damping provides a large degree of control over the expected performance of the structure. In this paper, a numerical study is presented on the performance of a seismically isolated highway bridge model that is subjected to various strong earthquake ground motions. The Negative Stiffness Devices (NSDs) are described along with their hysteretic behavior as obtained from a series of cyclic tests wherein the tests were conducted using a modified design of the NSDs (modified for testing within the bridge model). Using the results from the cyclic tests, numerical simulations of the seismic response of the isolated bridge model were conducted for various configurations (with/without negative stiffness devices and/or viscous dampers). The results demonstrate that the addition of negative stiffness devices reduces the base shear substantially, while the deck displacement is limited to acceptable values. This assessment was conducted as part of a NEES (Network for Earthquake Engineering Simulation) project which included shaking table tests of a quarter‐scale highway bridge model. Copyright © 2014 John Wiley & Sons, Ltd.     

Numerical modelling of aeolian erosion over a surface with non‐uniformly distributed roughness elements

The present study is focused on the analysis of the mean wall friction velocity on a surface including roughness elements exposed to a turbulent boundary layer. These roughness elements represent non‐erodible particles over an erodible surface of an agglomeration of granular material on industrial sites. A first study has proposed a formulation that describes the evolution of the friction velocity as a function of geometrical parameters and cover rate with different uniform roughness distributions. The present simulations deal with non‐uniform distributions of particles with a random sampling of diameters, heights, positions and arrangements. The evolution (relative to geometrical parameters of the roughness elements) of the friction velocity for several non‐uniform distributions of roughness elements was analysed by the equation proposed in the literature and compared to the results obtained with the numerical simulations. This comparison showed very good agreement. Thus, the formulation developed for uniform particles was found also to be valid for a larger spectrum of particles noted on industrial sites. The present work aims also to investigate in detail the fluid mechanics over several roughness particles. Copyright © 2013 John Wiley & Sons, Ltd.     

Possible change in distribution of seaweed, Sargassum horneri, in northeast Asia under A2 scenario of global warming and consequent effect on some fish

Global warming effects on seaweed beds are already perceptible. Their geographical distributions greatly depend on water temperatures. To predict future geographical distributions of brown alga, Sargassum horneri, forming large beds in the northwestern Pacific, we referred to future monthly surface water temperatures at about 1.1° of longitude and 0.6° of latitude in February and August in 2050 and 2100 simulated by 12 organizations under an A2 scenario of global warming. The southern limit of S. horneri distribution is expected to keep moving northward such that it may broadly disappear from Honshu Island, the Chinese coast, and Korean Peninsula in 2100, when tropical Sargassum species such as Sargassum tenuifolium may not completely replace S. horneri. Thus, their forests in 2100 do not substitute those of S. horneri in 2000. Fishes using the beds and seaweed rafts consisting of S. horneri in East China Sea suffer these disappearances.     

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长江流域气候变化高分辨率模拟与RCP4.5情景下的预估

基于长江流域142个气象站1986—2005年月降水和气温数据,评估由MPI-ESM-LR模式驱动的CCLM区域气候模式对长江流域气温和降水的模拟能力,并采用EDCDF法对气温和降水预估数据进行偏差校正。结果表明：该区域气候模式能较好地模拟出长江流域平均气温的季节变化和空间分布特征,但模拟值无论在季节还是年际尺度上均高于观测值。对降水而言,该模式不能较好地模拟出降水的季节分布特征,导致春季、冬季及年模拟值高于观测值,而夏季和秋季模拟值低于观测值。总体而言,该模式对气温的模拟效果相对较好。偏差校正后的预估结果表明：在RCP4.5情景下,长江流域未来（2016—2035年）平均气温相对于基准期（1986—2005年）将升高0.66℃,年降水量将减少2.2%。     

5个全球气候模式对中国东北地区地面温度的模拟与预估

利用5个全球气候模式和中国东北地区162个站点地面温度实测资料,评估全球气候模式和多模式集合平均对中国东北地区地面温度的模拟能力,并对SRES B1、A1B和A2排放情景下,中国东北地区未来地面温度变化进行预估。结果表明：全球气候模式能够较好地再现了东北地区地面温度的年变化和空间分布特征,但存在系统性冷偏差,模式对夏季地面温度模拟偏低1.16 ℃,优于冬季。预估结果表明,3种排放情景下21世纪中期和末期东北地区地面温度均将升高,末期增幅高于中期,冬季增幅高于其他季节, SRES A2排放情景下增幅最大,B1排放情景下最小;增温幅度自南向北逐渐增大,增温最显著地区位于黑龙江小兴安岭;21世纪末期3种情景下中国东北地区年平均地面温度将分别升高2.39 ℃(SRES B1)、3.62 ℃(SRES A1B)和4.43 ℃(SRES A2)。     

Modeling the effects of historical vegetation change on near-surface atmosphere in the northern Chihuahuan Desert

Our goal was to evaluate effects of broad-scale changes in vegetation from grasslands to shrublands over the past 150 years on near-surface atmosphere over the Jornada Experimental Range in the northern Chihuahuan Desert, using a regional climate model. Simulations were conducted using 1858 and 1998 vegetation maps, and data collected in the field. Overall, the vegetation shift led to small changes in sensible heat (SH) and an increase in latent heat (LH). The impacts of shrub encroachment depended on shrubland type: conversion from grass to mesquite cools the near-surface atmosphere and from grass to creosotebush warms it. Higher albedo of mesquite relative to grasses reduced available energy, which was dissipated mainly as LH due to the deeper root system in mesquite. In creosotebush-dominated areas, a decrease in albedo, an increase in roughness length and displacement height contributed to the SH increase and warmer temperatures. Sensitivity simulations showed that an increase in soil moisture content enhanced shrub LH and a reduction in mesquite cover enhanced the temperature differences. The observed shift in vegetation led to complex interactions between land and surface fluxes, demonstrating that vegetation itself is a weather and climate variable as it significantly influences temperature and humidity.     

Effects of adjusting cropping systems on utilization efficiency of climatic resources in Northeast China under future climate scenarios

Quantitatively evaluating the effects of adjusting cropping systems on the utilization efficiency of climatic resources under climate change is an important task for assessing food security in China. To understand these effects, we used daily climate variables obtained from the regional climate model RegCM3 from 1981 to 2100 under the A1B scenario and crop observations from 53 agro-meteorological experimental stations from 1981 to 2010 in Northeast China. Three one-grade zones of cropping systems were divided by heat, water, topography and crop-type, including the semi-arid areas of the northeast and northwest (III), the one crop area of warm–cool plants in semi-humid plain or hilly regions of the northeast (IV), and the two crop area in irrigated farmland in the Huanghuaihai Plain (VI). An agro-ecological zone model was used to calculate climatic potential productivities. The effects of adjusting cropping systems on climate resource utilization in Northeast China under the A1B scenario were assessed. The results indicated that from 1981 to 2100 in the III, IV and VI areas, the planting boundaries of different cropping systems in Northeast China obviously shifted toward the north and the east based on comprehensively considering the heat and precipitation resources. However, due to high temperature stress, the climatic potential productivity of spring maize was reduced in the future. Therefore, adjusting the cropping system is an effective way to improve the climatic potential productivity and climate resource utilization. Replacing the one crop in one year model (spring maize) by the two crops in one year model (winter wheat and summer maize) significantly increased the total climatic potential productivity and average utilization efficiencies. During the periods of 2011–2040, 2041–2070 and 2071–2100, the average total climatic potential productivities of winter wheat and summer maize increased by 9.36%, 11.88% and 12.13% compared to that of spring maize, respectively. Additionally, compared with spring maize, the average utilization efficiencies of thermal resources of winter wheat and summer maize dramatically increased by 9.2%, 12.1% and 12.0%, respectively. The increases in the average utilization efficiencies of precipitation resources of winter wheat and summer maize were 1.78 kg hm⁻² mm⁻¹, 2.07 kg hm⁻² mm⁻¹ and 1.92 kg hm⁻² mm⁻¹ during 2011–2040, 2041–2070 and 2071–2100, respectively. Our findings highlight that adjusting cropping systems can dominantly contribute to utilization efficiency increases of agricultural climatic resources in Northeast China in the future.