黄土丘陵区不同地貌单元土壤有机碳空间变异的尺度效应

运用地统计学和GIS相结合的方法,研究了黄土丘陵区县域不同地貌单元土壤有机碳空间变异的尺度效应,尺度划分为县域、县域上三种不同的地貌单元以及与地貌单元相对应的乡镇尺度,结果表明：①各个尺度下有机碳含量均偏低,完整地貌单元尺度与乡镇尺度有机碳均值与变异系数大小顺序不同;②高山区随着尺度的变化,自然因素对变异的影响程度没有显著变化,但低山丘陵区与丘陵沟壑区自然因素的影响程度减小,插值图表现出较小的研究面积有机碳含量信息更丰富;③县域尺度上海拔与土壤类型是导致变异的主控因素,在丘陵沟壑区,所研究的自然因素（海拔、土壤类型、土壤侵蚀程度、田面坡度、坡向）对其影响都不显著;在低山丘陵区,地貌单元上主控因子是海拔与土壤类型,而乡镇尺度上转化为田面坡度;在高山区,地貌单元上主控因子是土壤类型,但乡镇尺度上其主要影响因素变为土壤侵蚀程度。     

长江中下游洪水灾害成因及洪水特征模拟分析

长江中下游地区洪水灾害的发生是自然地理条件及人类活动共同作用的结果。流域水系构造和地理特征决定了其洪水多发性,气候变化和土地利用/地表覆盖变化导致该地区水循环过程发生较大改变,而大量水库、堤防的建设以及城市化的发展使得洪水过程发生显著变化,因此在各种因素的综合作用下,长江中下游地区近年来洪水灾害频繁发生。综述了气候变化对长江中下游降水的影响,探讨了长江中下游水系特征与洪水灾害的关系,分析了人类活动对洪水灾害的影响规律,在此基础上,开展了气候和下垫面特征变化条件下的暴雨洪水模拟研究,以长江下游太湖东苕溪流域的南苕溪为研究区,进行了流域降雨径流过程的动态模拟验证和特征分析,并取得了较满意的成果,从而为长江中下游地区防洪减灾研究打下了基础。     

Historical evidence of climatic variability and changes,and its effect on high-altitude regions: insights from Rara and Langtang,Nepal

ABSTRACT

Climatic variability and its effects have been experienced in the high-altitude regions of Nepal for some considerable time. Most of the studies on local people’s perception available so far in Nepal on climate include with respect to weather changes, and almost none have been verified with satellite imagery. This study thus attempts to combine meteorological and satellite imagery for comparing local people’s perception so that a more robust validation can be established. Both qualitative (transect walk, key informant interview, focus group discussion and institutional visit) and quantitative (meteorological and satellite image) data and techniques were employed. Local people from Rara and Langtang in Nepal shared their observations and perceptions on the changing climate for the last three decades and the effects on them and their local microclimate. Apart from temperature, rainfall and snowfall anomalies, locals observed changes in the water sources and increasing drought along with alteration in the phenology of tree and agricultural crops as well as vegetation range migration. Satellite image analysis also confirms a change in snow cover as notified by the local people. This study shows that local people’s knowledge could be considered as a complement to the observed scientific evidences of climate change science and their perceptions can be used reliably where scientific data are lacking. Finally, perceived climatic risks, current gaps and future opportunities are discussed and some recommendations are suggested.     

Evaluating the ecological benefits of wildfire by integrating fire and ecosystem simulation models

Fire managers are now realizing that wildfires can be beneficial because they can reduce hazardous fuels and restore fire-dominated ecosystems. A software tool that assesses potential beneficial and detrimental ecological effects from wildfire would be helpful to fire management. This paper presents a simulation platform called FLEAT (Fire and Landscape Ecology Assessment Tool) that integrates several existing landscape- and stand-level simulation models to compute an ecologically based measure that describes if a wildfire is moving the burning landscape towards or away from the historical range and variation of vegetation composition. FLEAT uses a fire effects model to simulate fire severity, which is then used to predict vegetation development for 1, 10, and 100 years into the future using a landscape simulation model. The landscape is then simulated for 5000 years using parameters derived from historical data to create an historical time series that is compared to the predicted landscape composition at year 1, 10, and 100 to compute a metric that describes their similarity to the simulated historical conditions. This tool is designed to be used in operational wildfire management using the LANDFIRE spatial database so that fire managers can decide how aggressively to suppress wildfires. Validation of fire severity predictions using field data from six wildfires revealed that while accuracy is moderate (30-60%), it is mostly dictated by the quality of GIS layers input to FLEAT. Predicted 1-year landscape compositions were only 8% accurate but this was because the LANDFIRE mapped pre-fire composition accuracy was low (21%). This platform can be integrated into current readily available software products to produce an operational tool for balancing benefits of wildfire with potential dangers.     

Air‐Water Temperature Relationships in the Trout Streams of Southeastern Minnesota's Carbonate‐Sandstone Landscape

Carbonate‐sandstone geology in southeastern Minnesota creates a heterogeneous landscape of springs, seeps, and sinkholes that supply groundwater into streams. Air temperatures are effective predictors of water temperature in surface‐water dominated streams. However, no published work investigates the relationship between air and water temperatures in groundwater‐fed streams (GWFS) across watersheds. We used simple linear regressions to examine weekly air‐water temperature relationships for 40 GWFS in southeastern Minnesota. A 40‐stream, composite linear regression model has a slope of 0.38, an intercept of 6.63, and R² of 0.83. The regression models for GWFS have lower slopes and higher intercepts in comparison to surface‐water dominated streams. Regression models for streams with high R² values offer promise for use as predictive tools for future climate conditions. Climate change is expected to alter the thermal regime of groundwater‐fed systems, but will do so at a slower rate than surface‐water dominated systems. A regression model of intercept vs. slope can be used to identify streams for which water temperatures are more meteorologically than groundwater controlled, and thus more vulnerable to climate change. Such relationships can be used to guide restoration vs. management strategies to protect trout streams.     

路域土壤重金属含量空间变异的影响因子

以纵向岭谷区景洪-思茅段公路沿线为研究区,通过公路不同地点样线布设,对不同土地类型、地形和公路距离下的98个样点进行了野外植被和环境因子调查及土壤采样,在土壤表层0～20cm重金属全量分析的基础上对影响其分布的环境因子做了相关分析,得出研究区路域土壤重金属污染的空间分异特征及其主要的影响因子.研究结果表明,公路沿线不同土地利用类型下土壤重金属元素的含量存在较大的差异,但不同类型下含量的变化趋势较为一致,草地重金属污染最为严重,而次生林,原始林重金属含量较低;土壤养分也受土地利用类型影响,但相关分析表明,除了pH值、总钾、总磷和重金属关系较为密切外,研究区其它土壤养分和重金属之间的含量相关不显著.重金属元素含量之间相关性显著,表明该段道路重金属污染具有同源性,即来自道路.距公路的距离对重金属含量影响较大,农田土壤重金属含量随距离公路增加逐渐降低,而自然土壤中,变化趋势呈波动趋势.进一步对自然土壤中重金属的影响因子做了分析,结果表明,地形影响重金属的含量垂直分异,而典范对应分析也显示研究区距离、地形、土地覆被和土壤特性共同作用于土壤污染的空间变异.影响程度为距离＞土地覆被＞地形＞土壤.     

A Perspective on Nonstationarity and Water Management1

Hirsch, Robert M., 2011. A Perspective on Nonstationarity and Water Management. Journal of the American Water Resources Association (JAWRA) 47(3):436‐446. DOI: 10.1111/j.1752‐1688.2011.00539.x Abstract: This essay offers some perspectives on climate‐related nonstationarity and water resources. Hydrologists must not lose sight of the many sources of nonstationarity, recognizing that many of them may be of much greater magnitude than those that may arise from climate change. It is paradoxical that statistical and deterministic approaches give us better insights about changes in mean conditions than about the tails of probability distributions, and yet the tails are very important to water management. Another paradox is that it is difficult to distinguish between long‐term hydrologic persistence and trend. Using very long hydrologic records is helpful in mitigating this problem, but does not guarantee success. Empirical approaches, using long‐term hydrologic records, should be an important part of the portfolio of research being applied to understand the hydrologic response to climate change. An example presented here shows very mixed results for trends in the size of the annual floods, with some strong clusters of positive trends and a strong cluster of negative trends. The potential for nonstationarity highlights the importance of the continuity of hydrologic records, the need for repeated analysis of the data as the time series grow, and the need for a well‐trained cadre of scientists and engineers, ready to interpret the data and use those analyses to help adjust the management of our water resources.     

Estimating the vulnerability of fifteen tree species under changing climate in Northwest North America

In the Pacific northwestern (PNW) region of North America, climatic conditions have significantly warmed since a predominantly cool phase of the Pacific North American circulation patterns between 1950 and 1975. What are the implications of this shift in climate for the vulnerability of native tree species? To address this question, we combined mechanistic and statistical models to assess where a variety of native tree species might be more vulnerable within their recorded ranges and where they might potentially migrate. For long-lived species that are well adapted to compete, seasonal differences in photosynthesis and water use offer insights helpful in predicting their distributions. To evaluate the general response of conifers to climatic variation across the region, we previously applied a process-based model (3-PG), to simulate the growth and maximum leaf area index that Douglas-fir could attain within recognized forested areas. We then constructed automated decision tree models to define and map the ecological distributions of 15 tree species based on differences in how photosynthesis was constrained by drought, daytime temperatures, high evaporative demand, and the frequency of frost. For the baseline climate period (1950-1975), the decision tree models predicted presence and absence of each species at ∼23,000 observations with an average accuracy of 81%, with an average kappa statistic of 0.74. In this paper the same models were run annually for the period between 1976 and 2006 for each species, and the areas defined as remaining suitable or becoming vulnerable to disturbance were identified based on whether more or less than half of the years fell within the originally defined limits. Based on these criteria, 70% of the species recorded ranges remained suitable, with 30% deemed vulnerable. Results varied notably by species with western red cedar and western hemlock remaining highly adapted, with potential for range expansion in area of up to 50% relative to the baseline period. In contrast, ponderosa pine, lodgepole pine, grand, and noble fir were classified as vulnerable with potential net contractions in their ranges. The analysis was extended through the rest of the 21st century using climatic projections from the Canadian global circulation model with a high fossil fuel emission scenario (A2) and compared to other previously published species range predictions.     

土壤养分空间估测方法研究综述

土壤养分是土壤提供的植物生长发育所必需的营养元素。由于受到自然因素和人为因素的共同作用,土壤养分具有高度的空间变异性。土壤的这种特性不仅表现在区域尺度上,而且也表现在田块尺度上。在研究方法上经历了从传统统计学到地统计学,再到神经网络、地理信息技术以及高精度曲面建模等新方法的不断改进过程。文章从地统计学方法引入到土壤养分空间变异研究中为出发点,论述了国内外基于地统计学的土壤养分空间变异的研究现状,主要包括利用地统计学方法来确定合理的土壤采样数目,土壤养分空间变异的定量化研究,土壤养分空间变异的尺度效应;然后简述了神经网络、地理信息技术、高精度曲面建模等技术在土壤养分空间变异研究中的研究现状和应用。最后对比分析了各种研究方法在应用中存在的缺陷,同时指明了今后应加强作物生长的不同时期土壤养分的空间变异性、土壤在四维空间尺度上的演变机理以及环境信息获取的不确定性等方面的研究。