基于BP神经网络的鄱阳湖水位模拟

考虑到鄱阳湖水位受流域五河与长江来水等多因素的共同作用而表现出高度非线性响应,采用典型的三层BPNN神经网络模型来模拟鄱阳湖水位与其主控因子之间的响应关系。分别将湖口、星子、都昌、棠荫和康山水位作为目标变量进行BPNN模型构建和适用性评估。结果显示：综合考虑流域五河及长江来水（汉口或九江）的BPNN水位模型,空间站点水位模拟精度（R2和Ens）可达090以上,各站点的均方根误差（RMSE）变化范围约050～10 m,若忽略长江来水的影响作用,仅将流域五河来水作为湖泊水位的主控影响因子,模型训练期与测试期的纳希效率系数（Ens）和确定性系数（R2）显著降低,且低于050,均方根误差（RMSE）也明显增大（124～288 m）,意味着综合考虑流域五河与长江来水是获取结构合理、精度保证的鄱阳湖水位模型的重要前提。同时建议针对鄱阳湖湖盆变化对水位的影响,尽可能选择一致性较好的长序列数据集来训练和测试BPNN模型。所构建的BPNN神经网络模型可进一步结合流域水文模型,用来预测气候变化与人类活动下流域径流变化对湖泊水位的潜在影响,也可作为一种有效的模型工具来回答当前鄱阳湖一些备受关注的热点问题,如定量区分流域五河与长江来水对湖泊洪枯水位的贡献分量,为湖泊洪涝灾害的防治和对策制定提供科学依据     

Small mammals as indicators of short-term and long-term disturbance in mixed prairie

Disturbance by military maneuvers over short and long time scales may have differential effects on grassland communities. We assessed small mammals as indicators of disturbance by military maneuvers in a mixed prairie in southern Oklahoma USA. We examined sites on two soil series, Foard and Lawton, across a gradient of disturbance intensity. A MANOVA showed that abundance of small mammals was associated (p = 0.03) with short-term (cover of vehicle tracks) disturbance but was not associated (p = 0.12) with long-term (loss of soil organic carbon, SOC) disturbance intensity. At the individual species level, Sigmodon hispidus (cotton rat) and Peromyscus maniculatus (deer mouse) occurred across all levels of disturbance and in both soil types. Only P. maniculatus abundance changed (p < 0.01) with short-term disturbance and increased by about one individual per 5% of additional track-cover. Abundance of P. maniculatus also increased (p = 0.04) by about three individuals per 1% increase in soil carbon. Chaetodipus hispidus (hispid pocket mouse) and Reithrodontomys fulvescens (fulvous harvest mouse) only occurred in single soil types limiting their potential as more general indicators. Abundance of P. maniculatus was positively related to shifts in plant species composition and likely reflected changes in vegetation structure (i.e. litter depth) and forage availability resulting from disturbance. Peromyscus maniculatus may be a useful biological indicator of ecosystem change because it responded predictably to both long-term and short-term disturbance and, when coupled with soil, plant, and disturbance history variables, can reveal land condition trends.     

OXIDIZED NITROGEN IN PRECIPITATION,THROUGHFALL, AND STREAMFALL FROM A FORESTED WATERSHED IN OKLAHOMA1

ABSTRACT: Oxidized nitrogen (nitrite + nitrate N) concentrations were measured from bulk precipitation, bulk through-fall, and streamflow in a 7.86 hectare forested watershed in southeastern Oklahoma during the wet season from March through June 1983. Oxidized nitrogen inputs comparable to results of other studies were recorded during the 19 rainstorms sampled. Oxidized nitrogen concentrations appeared to increase after rainfall interacted with the pine and hardwood canopies and were inversely related to both rainfall and through-fall depth. Oxidized N concentrations in streamflow were greatest during the rising limb of storm flow with subsequent decreases during the falling limb of storm hydrographs and lowest during base flow. The oxidized N inputs from bulk precipitation were considerably greater than outputs from streamflow resulting in a net retention of oxidized nitrogen within the watershed during the study period.     

基于SPEI的云南中部区域干旱时空变化特征分析

利用云南中部地区1961~2010年逐月降水和气温资料,采用降水距平百分率和历史旱情资料验证了标准化降水蒸散指数(Standardized Precipitation Evapotranspiration Index,SPEI)在该地区的适用性,并采用Mann-kendall突变检验、Morlet小波和经验正交函数(Empirical Orthogonal Function,EOF)等方法,分析了该地区干旱的时空演变特征,结果表明:(1)SPEI与降水距平百分率在时空上具有很好的相关性,验证了SPEI对降水变化的敏感性;(2)SPEI指数与历史旱情资料比较吻合,能够有效地反映云南中部区域的干旱特征;(3)年均SPEI呈波动下降趋势,干季SPEI降低趋势明显。年均SPEI存在着24a的主周期和9a的次周期,并于1977年发生了突变,此后开始降低,在整体上呈现出干旱化的趋势;(4)从SPEI的空间分布特征来看,其在整体上受大尺度气候系统的影响表现出一致的下降趋势,而在区域内部则表现出东南-西北(干热河谷)的反向结构差异。     

THE IMPACTS OF CLIMATIC CHANGES FOR WATER RESOURCES OF THE COLORADO AND SACRAMENTO-SAN JOAQUIN RIVER BASINS1

ABSTRACT: A wide variety of regional assessments of the water-related impacts of climatic change have been done over the past two decades, using different methods, approaches, climate models, and assumptions. As part of the Water Sector research for the National Assessment of the Implications of Climatic Variability and Change for the United States, several major summaries have been prepared, looking at the differences and similarities in results among regional research projects. Two such summaries are presented here, for the Colorado River Basin and the Sacramento River Basin. Both of these watersheds are vitally important to the social, economic, and ecological character of their regions; both are large snowmelt-driven basins; both have extensive and complex water management systems in place; and both have had numerous, independent studies done on them. This review analyzes the models, methods, climate assumptions, and conclusions from these studies, and places them in the context of the new climate scenarios developed for the National Assessment. Some significant and consistent impacts have been identified for these basins, across a wide range of potential climate changes. Among the most important is the shift in the timing of runoff that results from changes in snowfall and snowmelt dynamics. This shift has been seen in every regional result across these two basins despite differences in models and climate change assumptions. The implications of these impacts for water management, planning, and policy are discussed.     

Analysis of Meteorological Drought Pattern During Different Climatic and Cropping Seasons in Bangladesh

Drought is one of the most frequent natural disasters in Bangladesh which severely affect agro‐based economy and people's livelihood in almost every year. Characterization of droughts in a systematic way is therefore critical in order to take necessary actions toward drought mitigation and sustainable development. In this study, standardized precipitation index is used to understand the spatial distribution of meteorological droughts during various climatic seasons such as premonsoon, monsoon, and winter seasons as well as cropping seasons such as Pre‐Kharif (March‐May), Kharif (May‐October), and Rabi (December‐February). Rainfall data collected from 29 rainfall gauge stations located in different parts of the country were used for a period of 50 years (1961‐2010). The study reveals that the spatial characteristics of droughts vary widely according to season. Premonsoon droughts are more frequent in the northwest, monsoon droughts mainly occur in the west and northwest, winter droughts in the west, and the Rabi and Kharif droughts are more frequent in the north and northwest of Bangladesh. It is expected that the findings of the study will support drought monitoring and mitigation activities in Bangladesh.     

1780-1819年华北平原水旱灾害社会响应方式的转变

历史时期水旱灾害的社会响应典型案例重建是气候变化影响与适应研究的重要方向。选取1780-1819年间华北平原发生的4次典型水旱灾害(1785、1792、1813年旱灾及1801年水灾),基于清代档案资料和历史气候重建结果提取代用指标,对其灾情严重程度、政府救灾力度和灾民行为进行了量化描述和对比分析,发现:①4次灾害中赈济密度(赈灾物资数/成灾州县数)逐次下降,1813年旱灾中降至不足1785年旱灾的1/6,政府救灾力度遭到严重削弱;②灾民行为日益失控,从1792年旱灾和1801年水灾中的大规模跨区域迁徙,发展到1813年旱灾中大量加入盗匪和起义军,走向暴力。这一转变的发生,是在自然(气候突变、灾害增多)、社会(政府财政危机、人地矛盾激化)不利背景之下,政府与灾民的互动关系日趋消极的结果。     

Assessing Retrospective National Water Model Streamflow with Respect to Droughts and Low Flows in the Colorado River Basin

Streamflow monitoring in the Colorado River Basin (CRB) is essential to ensure diverse needs are met, especially during periods of drought or low flow. Existing stream gage networks, however, provide a limited record of past and current streamflow. Modeled streamflow products with more complete spatial and temporal coverage (including the National Water Model [NWM]), have primarily focused on flooding, rather than sustained drought or low flow conditions. Objectives of this study are to (1) evaluate historical performance of the NWM streamflow estimates (particularly with respect to droughts and seasonal low flows) and (2) identify characteristics relevant to model inputs and suitability for future applications. Comparisons of retrospective flows from the NWM to observed flows from the United States Geological Survey stream gage network over 22 years in the CRB reveal a tendency for underestimating low flow frequency, locations with low flows, and the number of years with low flows. We found model performance to be more accurate for the Upper CRB and at sites with higher precipitation, snow percent, baseflow index, and elevations. Underestimation of low flows and variable model performance has important implications for future applications: inaccurate evaluations of historical low flows and droughts, and less reliable performance outside of specific watershed/stream conditions. This highlights characteristics on which to focus future model development efforts.     

Development of a Grassland Integrity Index Based on Breeding Bird Assemblages

We utilized landscape and breeding bird assemblage data from three Breeding Bird Survey (BBS) routes sampled from 1965–1995 to develop and test a grassland integrity index (GII) in a mixed-grass prairie area of Oklahoma. The overall study region is extensively fragmented from long-term agricultural activity, and native habitat remnants have been degraded by recent encroachment of woody vegetation, namely eastern redcedar (Juniperus virginiana L.). The 50 individual bird survey points along the BBS routes, known as stops, were used as sample sites. Our process first focused on developing a grassland disturbance index (GDI) as a measure of cumulative landscape disturbances for these sites. The GDI was based on five key landscape variables identified in an earlier species-level study of long-term avian community dynamics: total tree, shrub, and herbaceous vegetation cover indices, overall mean landscape patch size, and grassland patch core size. The GII was then developed based on breeding bird assemblage data. Assemblages were based on commonly used response guilds reflective of five avian life history parameters: foraging mode/location, nesting location, habitat specificity, migratory pattern, and dietary guild. We tested the response of 78 candidate assemblage metrics to the GDI, and eliminated those with no or poor response or with high correlations (redundant), resulting in 13 metrics for use in the final index. Individual metric scores were scaled to fall between 0 and 10, and the cumulative index to range from 0 to 100. Although broader application and refinement are possible, the avian-based GII has an advantage over labor-intensive, habitat-based monitoring in that the GII is derived from readily available long-term BBS data. Therefore, the GII shows promise as an inexpensive tool that could easily be applied over other areas to monitor changes in regional grassland conditions.     

洞庭湖近年干旱与三峡蓄水影响分析

季节性水文干旱是洞庭湖近年突出的水情问题,并因三峡影响而倍受关注。基于洞庭湖水文干旱的关注焦点（湿地生态影响）及其与湖泊水情的对应关系,建立了湖泊滩地出露与持续时间为依据的干旱度量指标;并利用水文分析方法,揭示了洞庭湖水文干旱发生的时空特点和水情机制;最后,基于BP神经网络模型获取的三峡水库蓄水对洞庭湖的水位影响量化了三峡水库秋季蓄水对湖区干旱的贡献分量。结果认为：（1）2000年后,洞庭湖的干旱频次明显增多、旱情加重,干旱程度以西洞庭最剧,东洞庭次之,南洞庭最轻;（2）洞庭湖不同湖区干旱成因存在一定差异,其中全湖的春旱基本由洞庭湖流域来水偏少引起,而东洞庭湖秋旱主要由长江来水减少引起,西、南洞庭湖秋旱则由长江和洞庭湖流域来水共同减少形成;（3）三峡水库蓄水对东洞庭湖秋旱起到一定的加重作用,但并非洞庭湖近年干旱的主要因素