A Streamflow Forecasting Framework using Multiple Climate and Hydrological Models1

Abstract: Water resources planning and management efficacy is subject to capturing inherent uncertainties stemming from climatic and hydrological inputs and models. Streamflow forecasts, critical in reservoir operation and water allocation decision making, fundamentally contain uncertainties arising from assumed initial conditions, model structure, and modeled processes. Accounting for these propagating uncertainties remains a formidable challenge. Recent enhancements in climate forecasting skill and hydrological modeling serve as an impetus for further pursuing models and model combinations capable of delivering improved streamflow forecasts. However, little consideration has been given to methodologies that include coupling both multiple climate and multiple hydrological models, increasing the pool of streamflow forecast ensemble members and accounting for cumulative sources of uncertainty. The framework presented here proposes integration and offline coupling of global climate models (GCMs), multiple regional climate models, and numerous water balance models to improve streamflow forecasting through generation of ensemble forecasts. For demonstration purposes, the framework is imposed on the Jaguaribe basin in northeastern Brazil for a hindcast of 1974‐1996 monthly streamflow. The ECHAM 4.5 and the NCEP/MRF9 GCMs and regional models, including dynamical and statistical models, are integrated with the ABCD and Soil Moisture Accounting Procedure water balance models. Precipitation hindcasts from the GCMs are downscaled via the regional models and fed into the water balance models, producing streamflow hindcasts. Multi‐model ensemble combination techniques include pooling, linear regression weighting, and a kernel density estimator to evaluate streamflow hindcasts; the latter technique exhibits superior skill compared with any single coupled model ensemble hindcast.     

Effect of the Spatial Variability of Land Use,Soil Type,and Precipitation on Streamflows in Small Watersheds1

Abstract: The spatial variability of the data used in models includes the spatial discretization of the system into subsystems, the data resolution, and the spatial distribution of hydrologic features and parameters. In this study, we investigate the effect of the spatial distribution of land use, soil type, and precipitation on the simulated flows at the outlet of “small watersheds” (i.e., watersheds with times of concentration shorter than the model computational time step). The Soil and Water Assessment Tool model was used to estimate runoff and hydrographs. Different representations of the spatial data resulted in comparable model performances and even the use of uniform land use and soil type maps, instead of spatially distributed, was not noticeable. It was found that, although spatially distributed data help understand the characteristics of the watershed and provide valuable information to distributed hydrologic models, when the watershed is small, realistic representations of the spatial data do not necessarily improve the model performance. The results obtained from this study provide insights on the relevance of taking into account the spatial distribution of land use, soil type, and precipitation when modeling small watersheds.     

Evaluating and Extending CLIGEN Precipitation Generation for the Loess Plateau of China1

Abstract: Climate generator (CLIGEN) is widely used in the United States to generate long‐term climate scenarios for use with agricultural systems models. Its applicability needs to be evaluated for use in a new region or climate. The objectives were to: (1) evaluate the reproducibility of the latest version of CLIGEN v5.22564 in generating daily, monthly, and yearly precipitation depths at 12 stations, as well as storm patterns including storm duration (D), relative peak intensity (ip), and peak intensity (rp) at 10 stations dispersed across the Loess Plateau and (2) test whether an exponential distribution for generating D and a distribution‐free approach for inducing desired rank correlation between precipitation depth and D can improve storm pattern generations. Mean absolute relative errors (MAREs) for simulating daily, monthly, annual, and annual maximum daily precipitation depth across all 12 stations were 3.5, 1.7, 1.7, and 5.0% for the mean and 5.0, 4.5, 13.0, and 13.6% for the standard deviations (SD), respectively. The model reproduced the distributions of monthly and annual precipitation depths well (p > 0.3), but the distribution of daily precipitation depth was less well produced. The first‐order, two‐state Markov chain algorithm was adequate for generating precipitation occurrence for the Loess Plateau of China; however, it underpredicted the longest dry periods. The CLIGEN‐generated storm patterns poorly. It underpredicted mean and SD of D for storms ≥10 mm by ?60.4 and ?72.6%, respectively. Compared with D, ip, and rp were slightly better reproduced. The MAREs of mean and SD were 21.0 and 52.1% for ip, and 31.2 and 55.2% for rp, respectively. When an exponential distribution was used to generate D, MAREs were reduced to 2.6% for the mean and 7.8% for the SD. However, ip estimation became much worse with MAREs being 128.9% for the mean and 241.1% for the SD. Overall, storm pattern generation needs improvement. For better storm pattern generation for the region, precipitation depth, D, and rp may be generated correlatively using Copula methods.     

黄土高原植被类型变化和空间分布对气象因子变化的响应

利用基于GIS的黄土高原植被类型分布图,结合黄土高原地区标准气象站的气象因子资料,对黄土高原植被类型变化和空间分布对气象因子变化的响应关系进行了分析。结果显示:从东南到西北,年降水量、月平均最高气温、月平均最低气温逐渐减少,年平均气温、全年日照时数、全年最大蒸散量、平均风速逐渐增加,植被类型由东南湿润半湿润森林、半干旱森林草原往西北转变成轻干旱、重半干旱的温性草原、干旱的荒漠半荒漠植被。     

纳米零价铁颗粒除磷反应机理

从溶液化学与固相表征两方面对纳米零价铁(NZVI)去除水中磷酸根(PO3-4)的机理进行初步探究。分别研究不同初始p H值、溶解氧(DO)对NZVI除磷效果的影响,结果表明,酸性环境(p H为3.0~7.0)有利于NZVI除磷,且初始p H值越低,磷去除率越高;好氧环境较厌氧环境更利于磷的去除,DO8.0 mg/L时对磷酸根的去除率是厌氧条件(DO0.1 mg/L)下的2倍。采用Na OH对反应后含磷NZVI进行解析,发现磷解析率不到30%,说明吸附并非NZVI除磷惟一作用机理。微米铁、NZVI和Ca(OH)2等7种不同去除材料中以Ca(OH)2的共沉淀作用去除率最大(99.9%),NZVI次之(87.2%),表明NZVI除磷机理中还存在共沉淀作用。采用多种固相表征手段对NZVI除磷前后进行分析:扫描电子显微镜(SEM)显示反应后出现不规则颗粒;X射线衍射(XRD)表明Fe3(PO4)2是主要反应产物;X射线光电子能谱(XPS)分析未发现磷被还原成低价态。研究表明,NZVI可有效去除水中磷酸根,主要去除机理包括:NZVI对磷酸根的吸附作用、NZVI在水中腐蚀产生的Fe2+离子对磷酸根的化学沉淀作用及铁氢氧化物与磷酸根的共沉淀作用。     

Changes in the chemical composition of water-extractable organic matter during composting: distribution between stable and labile organic matter pools

Aerobic decomposition and stabilization of organic matter during the composting of waste materials is primarily due to the biochemical transformation of water-soluble compounds in the liquid phase by the microbial biomass. For this reason water-soluble organic matter represents the most active fraction of compost, both biologically and chemically, and thus should directly reflect the biochemical alteration of organic matter. This work aims to elucidate the microbial-mediated processes responsible for the distribution of soluble organic matter between stable and labile pools with composting time. Accordingly, chemical analysis as well as UV absorption, and ¹H and ¹³C-NMR spectroscopy of samples collected during the industrial composting of urban waste revealed microbial induced transformation of water-extractable organic matter over time. The chemical composition changed from labile, hydrophilic, plant-derived organic compounds in the beginning to predominately stable, hydrophobic moieties comprising lignin-derived phenols and microbially-derived carbohydrates at later stages of composting.     

酸性蚀刻废液处理的试验研究

通过室内试验,比较置换、中和-置换及化学沉淀-电絮凝处理方法对废蚀刻液的处理效果.结果表明,化学沉淀-电絮凝工艺的处理效果最好,其适宜工艺条件为废蚀刻液pH=6 0～7 5、电絮凝电流密度50 mA/cm2和电絮凝作用15 min,此时COD和Cu2+的去除率分别达98 7%和99 98%.研究表明,经过化学沉淀-电絮凝工艺处理的酸性蚀刻废液可达到排放标准,同时化学沉淀过程中产生的沉淀物经处理后可得到硫酸铜产品.     

Two modelling approaches to water-quality simulation in a flooded iron-ore mine (Saizerais, Lorraine, France): a semi-distributed chemical reactor model and a physically based distributed reactive transport pipe network model

The flooding of abandoned mines in the Lorraine Iron Basin (LIB) over the past 25 years has degraded the quality of the groundwater tapped for drinking water. High concentrations of dissolved sulphate have made the water unsuitable for human consumption. This problematic issue has led to the development of numerical tools to support water-resource management in mining contexts. Here we examine two modelling approaches using different numerical tools that we tested on the Saizerais flooded iron-ore mine (Lorraine, France). A first approach considers the Saizerais Mine as a network of two chemical reactors (NCR). The second approach is based on a physically distributed pipe network model (PNM) built with EPANET 2 software. This approach considers the mine as a network of pipes defined by their geometric and chemical parameters. Each reactor in the NCR model includes a detailed chemical model built to simulate quality evolution in the flooded mine water. However, in order to obtain a robust PNM, we simplified the detailed chemical model into a specific sulphate dissolution-precipitation model that is included as sulphate source/sink in both a NCR model and a pipe network model. Both the NCR model and the PNM, based on different numerical techniques, give good post-calibration agreement between the simulated and measured sulphate concentrations in the drinking-water well and overflow drift. The NCR model incorporating the detailed chemical model is useful when a detailed chemical behaviour at the overflow is needed. The PNM incorporating the simplified sulphate dissolution-precipitation model provides better information of the physics controlling the effect of flow and low flow zones, and the time of solid sulphate removal whereas the NCR model will underestimate clean-up time due to the complete mixing assumption. In conclusion, the detailed NCR model will give a first assessment of chemical processes at overflow, and in a second time, the PNM model will provide more detailed information on flow and chemical behaviour (dissolved sulphate concentrations, remaining mass of solid sulphate) in the network. Nevertheless, both modelling methods require hydrological and chemical parameters (recharge flow rate, outflows, volume of mine voids, mass of solids, kinetic constants of the dissolution-precipitation reactions), which are commonly not available for a mine and therefore call for calibration data.     

浙江江山化工股份有限公司污水站一期调试运行

通过对浙江江山化工股份有限公司污水站一期工程3个多月的调试,证明复合厌氧反应器(HAR) 多段好氧工艺处理高浓度有机废水是切实可行的.新型HAR污水站常温下100 d左右可以顺利启动,在进水量675 m3/d、平均容积负荷(以COD计)2.72 kg/(m3·d)条件下,平均COD去除率为35.47%,平均有机胺转化率为39.50%.启动后组合系统COD去除率可达90%以上,出水达到<污水综合排放标准>三级标准.化学沉淀去除NH3-N是出水顺利达标和好氧池稳定、高效运行的关键.尽可能控制并减少磷酸盐等加药量,以防止剩余磷的二次污染.     

Atmospheric heavy metal deposition accumulated in rural forest soils of southern Scandinavia

Thirty-three years of measurements of atmospheric heavy metal (HM) deposition (bulk precipitation) in Denmark combined with European emission inventories form the basis for calculating a 50-year accumulated atmospheric input to a remote forest plantation on the island of Laesoe. Soil samples taken in two depths, 0-10cm and 10-20cm, at eight forest sites at the island were used to determine the increase in HM content in the eolian deposited top soils of the plantation. Concentrations of lead (Pb), cadmium (Cd), copper (Cu), zinc (Zn), vanadium (V), nickel (Ni) and arsenic (As) were determined in atmospheric deposition and in soils. The accumulated atmospheric deposition is of the same magnitude as the increase of these metals in the top soil.