Agro-ecosystem modeling can aid in the optimization of biomass feedstock supply

Recent European Directives promoted the development of biofuels, requesting mandatory limits to their emissions ot greenhouse gases (GHG). Second-generation biofuels based on lignocellulosic biomass are prime candidates but their GHG emissions are variable and uncertain. Agro-ecosystem modeling can capture them and the performance of biofuel feedstocks.This study aimed at optimizing feedstock supply for a bioethanol unit in France, from agricultural residues, annual and perennial crops. Their productivity and environmental impacts were modelled on a regional scale using geo-referenced data on soil properties, crop management, land-use and future weather data. Several supply scenarios were tested. Cereal straw was the most efficient feedstock but had a low availability, and only miscanthus could meet the bioethanol plant's demand. Sorghum combined poor yields and high GHG emissions compared by miscanthus and triticale. A mix of three biomass sources used less than 3% of the regional agricultural land while abating GHG emissions by 60%.     

A numerical approach for planning offshore wind farms from regional to local scales over the Mediterranean

Renewable energy resources, such as wind, are available worldwide. Locating areas with high and continual wind sources are crucial in pre-planning of wind farms. Vast offshore areas are characterized by higher and more reliable wind resources in comparison with continental areas. However, offshore wind energy production is in a quite preliminary phase. Elaborating the potential productivity of wind farms over such areas is challenging due to sparse in situ observations. The Mediterranean basin is not an exception. In this study we are proposing numerical simulations of near-surface wind fields from regional climate models (RCMs) in order to obtain and fill the gaps in observations over the Mediterranean basin. Four simulations produced with two regional climate models are examined here. Remote sensing observations (QuikSCAT satellite) are used to assess the skill of the simulated fields. A technique for estimating the potential energy from the wind fields over the region is introduced. The wind energy potential atlas and the map of a wind turbine's functional range are presented, locating the potentially interesting sub-regions for wind farms. The ability of models to reproduce the annual cycle and the probability density function of wind speed anomalies are detailed for specified sub-regions.     

Simulation of the East Asian Subtropical Westerly Jet Stream with GFDL AGCM (AM2.1)

The present study validated the capability of the AM2.1, a model developed at NOAA's Geophysical Fluid Dynamics Laboratory (GFDL), in reproducing the fundamental features of the East Asian Subtropical Westerly Jet Stream (EASWJ). The main behaviors of the EASWJ are also investigated through the reanalysis of observational NCEP/NCAR data. The mean state of the EASWJ, including its intensity, location, structure, and seasonal evolution is generally well-portrayed in the model. Compared with the observation, the model tends to reproduce a weaker jet center. And, during summer, the simulated jet center is northward-situated. Results also demonstrate the model captures the variability of EASWJ during summer well. The results of the empirical orthogonal function (EOF) applied on the zonal wind at 200hPa (U200) over East Asia for both the observation and simulation indicate an inter-decadal shift around the late 1970s. The correlation coefficient between the corresponding principle components is as great as 0.42 with significance at the 99% confidence level.     

Projected climate change impacts on hydrologic flow regimes in the Great Plains of Kansas

Alteration of flow regimes due to change in climate and its potential impact on habitat and species has become a major cause of concern for riverine ecosystems. Areas that are more vulnerable to such changes are semiarid river systems or regions experiencing intermittent flow and cyclic droughts. Although ecological changes are expected to occur with flow regime alterations, the biological changes cannot be predicted until the flow in such regions is analysed. This study addresses this concern by providing an analysis of flow for a semiarid river basin in the Central Great Plains from a 50 and 100‐year projection climate data. The projected data for these two periods are then compared with 30‐year historical data to determine changes in flow. Five major components of flow regime, magnitude, duration, and timing of annual extreme water conditions, frequency and duration of high and low pulses, and rate and frequency of water condition changes, were examined with respect to climate change for their impact on the ecology of the basin. This analysis strongly suggests that inter‐ and intra‐annual changes in flow regimes will result in the intensified drying of the basin represented by the increased number of low flow periods followed by higher occurrences of high flow events of shorter duration with expected changes in climate.     

An Evaluation of CMIP5 GCM Simulations over the Athabasca River Basin,Canada

Long‐term hydrological forecasting, water resources management and other climate change impacts or adaptation analysis studies on large continental river basins, for example, the Athabasca River Basin (ARB) in Canada, desire a reliable climatic projection. This usually relies on general circulation models (GCMs) in the fifth phase of the Coupled Model Intercomparison Project (CMIP5). However, there is a lack of a systematic evaluation of CMIP5 GCM performances over the ARB that vary with multiple factors, for example, statistical metrics, temporal scales and spatial locations, challenging the reliability of water‐related or other studies over the ARB. For this gap to be filled, six CMIP5 GCMs, namely, IPSL‐CM5A‐LR, IPSL‐CM5A‐MR, MIROC‐ESM‐CHEM, MIROC5, GFDL‐ESM2G and GFDL‐ESM2M, and their ensemble mean are selected according to data availabilities of representative climate variables: Tmin, Tmax and Prec (TTP). Accuracies of the selected CMIP5 GCMs in reproducing TTP over the ARB are evaluated comprehensively. The ensemble mean cannot outperform any GCM in all cases in the ARB, although its overall accuracy seems to be higher in consideration of all cases. These accuracies vary with TTP, locations, metrics and scales. For instance, ESM2G shows the highest accuracies in reproducing monthly/seasonal variability and magnitudes of grid‐averaged TTP and inter‐annual variability of grid‐averaged annual means of Tmax; CM5A‐LR in multi‐year‐averaged spatial variability of TTP and magnitudes of spatially distributed multi‐year‐averaged Tmax; while the ensemble mean only in some aspects, for example, intraseasonal variability and magnitudes of TTP and inter‐annual variability and magnitudes of grid‐averaged annual means of TTP. GCMs should be systematically integrated according to accuracy variations. Multiple statistical metrics are recommended in GCM evaluations. These findings facilitate water resources systems analyses and other related studies in the ARB. Copyright © 2017 John Wiley & Sons, Ltd.     

全球气候变化对区域水资源影响研究进展综述

气候变化将改变全球水循环的现状,导致水资源时空分布的重新分配.并对降水蒸散发、径流等造成直接影响.国内外学者越来越重视气候变化对区域水资源影的研究,但是研究中存在着薄弱环节,首先是气候模型和水文模型耦合中出现的精确问题,其次是研究主要集中在气候变化对区域平均径流变化的影响.深入分存在的不足之处,旨在综合国内外研究经验,促进我国相关研究的发展.     

统计降尺度方法及其评价指标比较研究

针对目前气候变化对水资源影响研究中关注的问题,以汉江白河上游为研究对象,比较研究统计降尺度方法及其评价指标。以美国环境预报中心/美国国家大气研究中心全球再分析资料、CGCM3和HadCM3的A2情景为大尺度气候背景资料,应用SSVM和SDSM统计降尺度方法对大尺度气候因子进行尺度降解,得到降水情景序列后作为水文模型的输入,通过模拟径流比较分析统计降尺度方法的优劣。研究结果表明,由不同统计降尺度方法得到的降水作为水文模型输入,模拟径流的结果相差很大;对广泛应用于统计降尺度方法的降水模拟评价指标和径流模拟结果进行比较,发现所采用的降水评价指标侧重于考虑降水的统计分布特征,不能完整地描述降水过程特性。分析认为,径流模拟结果应该作为气候变化对径流影响研究中统计降尺度方法评价的重要参考。     

大容量直流输电系统的受端接入模式比较

首先分析了大容量直流输电(large-capacity high voltage direct current,large-capacity HVDC)系统常规接入模式(general connection mode,GCM)、分极接入模式(separate poles mode,SPM)和分层接入模式(hierarchical connection mode,HCM)的结构特点,对比了3种接入模式对系统中其他直流系统多馈入短路比(multi-feed short-circuit ratio,M ISCR)的影响,并得到落点选择的约束条件,使受端交流系统对直流系统的电压支撑能力整体提升,较好地平衡了限制短路电流与增加多馈入短路比间的矛盾。之后,提出了基于最大功率曲线法的静态稳定接纳系数指标用于判断受端电网接纳直流功率的能力。最后,结合南方电网2020年的规划数据,从多个方面对比分析了3种接入模式的优缺点,为直流系统接入模式的规划提供决策参考和技术支撑。     

Modelling the effects of climate change on the energy system—A case study of Norway

The overall objective of this work is to identify the effects of climate change on the Norwegian energy system towards 2050. Changes in the future wind- and hydro-power resource potential, and changes in the heating and cooling demand are analysed to map the effects of climate change. The impact of climate change is evaluated with an energy system model, the MARKAL Norway model, to analyse the future cost optimal energy system. Ten climate experiments, based on five different global models and six emission scenarios, are used to cover the range of possible future climate scenarios and of these three experiments are used for detailed analyses. This study indicate that in Norway, climate change will reduce the heating demand, increase the cooling demand, have a limited impact on the wind power potential, and increase the hydro-power potential. The reduction of heating demand will be significantly higher than the increase of cooling demand, and thus the possible total direct consequence of climate change will be reduced energy system costs and lower electricity production costs. The investments in offshore wind and tidal power will be reduced and electric based vehicles will be profitable earlier.     

IEEE802.1AE中GCM的高速硬件实现

该文设计了一种适用于IEEE802.1AE协议的GCM高速硬件结构。GCM的核心模块包括AES和Ghash两部分。该文中Ghash模块采用了一种新型的并行乘加器,可以同时处理多组数据,而不需要预先确定等待处理的分组数据总数;为了支持密钥每个时钟周期不断变化,AES中密钥扩展模块采用了循环展开结构。该文采用二度并行的Ghash模块实现了GCM高速加密电路,使用Fujitsu 0.13 m 1.2 V 1P8M CMOS工艺进行逻辑综合,得到吞吐率为97.9 Gbps,面积为547 k门,时钟频率达到764.5 MHz。