The potential for short-rotation woody crops to reduce U.S. CO2 emissions

Short-rotation woody crops (SRWC) could potentially displace fossil fuels and thus mitigate CO₂ buildup in the atmosphere. To determine how much fossil fuel SRWC might displace in the United States and what the associated fossil carbon savings might be, a series of assumptions must be made. These assumptions concern the net SRWC biomass yields per hectare (after losses); the amount of suitable land dedicated to SRWC production; wood conversion efficiencies to electricity or liquid fuels; the energy substitution properties of various fuels; and the amount of fossil fuel used in growing, harvesting, transporting, and converting SRWC biomass. Assuming the current climate, present production, and conversion technologies and considering a conservative estimate of the U.S. land base available for SRWC (14 × 10⁶ ha), we calculate that SRWC energy could displace 33.2 to 73.1 × 10⁶ Mg of fossil carbon releases, 3–6% of the current annual U.S. emissions. The carbon mitigation potential per unit of land is larger with the substitution of SRWC for coal-based electricity production than for the substitution of SRWC-derived ethanol for gasoline. Assuming current climate, predicted conversion technology advancements, an optimistic estimate of the U.S. land base available for SRWC (28 × 10⁶ ha), and an optimistic average estimate of net SRWC yields (22.4 dry Mg/ha), we calculate that SRWC energy could displace 148 to 242 × 10⁶ Mg of annual fossil fuel carbon releases. Under this scenario, the carbon mitigation potential of SRWC-based electricity production would be equivalent to about 4.4% of current global fossil fuel emissions and 20% of current U.S. fossil fuel emissions.Research sponsored by the Biofuels Systems Division, U.S. Department of Energy, under contract DE-AC05-840R21400 with Martin Marietta Energy Systems, Inc. Environmental Sciences Division Publication number 3952.     

基于随机暴雨移置方法的城市设计暴雨分析

城市地区暴雨洪灾发生频繁，合理计算设计暴雨是解决城市洪涝的重要前提。采用随机暴雨移置方法（Stochastic Storm Transposition，SST），设定暴雨移置区并提取出暴雨目录，通过区域性概率重采样与暴雨空间变换相结合的方式进行降雨频率分析，估计本地化的极端暴雨频率。以上海地区为例，研究发现暴雨移置区内暴雨分布具有空间异质性，暴雨随机移置概率不均，计算得到的设计暴雨方案包含了降雨时空分布信息，在不同重现期下设计暴雨的时空结构存在变异性，说明传统方法中采用的简化雨型和均一化空间分布假设会增加设计暴雨的不确定性。     

A stochastic distributed model of soil erosion by overland flow

A model has been built to simulate runoff and erosion on slopes of varying form with soil of varying hydraulic conductivity, porosity, storage capacity, and particle size distribution. The model is based on known physical laws and takes into account spatially dependent random variation in the initial conditions of the soil. The rainfall is similarly both random and autocorrelated in space. Detailed results show how runoff is generated as a result of slow conductivity and high water table, how this leads to erosion, the degradation of the land surface, the capture of flow lines, and the development of networks of rills. The last accords well with results from laboratory experiments. Changing the initial conditions produces results that accord with intuition and reality.     

A note on quaternary climate modelling using Boolean delay equations

The Boolean delay equation model of Ghil et al. for the study of Quaternary ice ages has been re-examined and also extended to include a hydrological feedback mechanism that directly influences the thermohaline circulation. For the basic Ghil et al. model (with the original and with corrected time delays), we show that the maximum duration for a high ice volume state depends continuously but not monotonically on the time delays of the problem. In particular, both short spiky glacials and longer glacials can be obtained from identical parameter values by simply choosing different initial conditions. In the extended model, we find that an additional temperature-hydrology-ocean feedback mechanism tends to generate longer glacials, but in neither case do the average time scales of model variability compare favourably with those of the major Quarternary glacials.