REGIONAL HYDROLOGIC RESPONSE OF LOBLOLLY PINE TO AIR TEMPERATURE AND PRECIPITATION CHANGES1

ABSTRACT: Large deviations in average annual air temperatures and total annual precipitation were observed across the southern United States during the last 50 years, and these fluctuations could become even larger during the next century. We used PnET-IIS, a monthly time-step forest process model that uses soil, vegetation, and climate inputs to assess the influence of changing climate on southern U.S. pine forest water use. After model predictions of historic drainage were validated, the potential influences of climate change on loblolly pine forest water use was assessed across the region using historic (1951 to 1984) monthly precipitation and air temperature which were modified by two general circulation models (GCMs). The GCMs predicted a 3.2°C to 7.2°C increase in average monthly air temperature, a -24 percent to + 31 percent change in monthly precipitation and a -1 percent to + 3 percent change in annual precipitation. As a comparison to the GCMs, a minimum climate change scenario using a constant 2°C increase in monthly air temperature and a 20 percent increase in monthly precipitation was run in conjunction with historic climate data. Predicted changes in forest water drainage were highly dependent on the GCM used. PnET-IIS predicted that along the northern range of loblolly pine, water yield would decrease with increasing leaf area, total evapotranspiration and soil water stress. However, across most of the southern U.S., PnET-IIS predicted decreased leaf area, total evapotranspiration, and soil water stress with an associated increase in water yield. Depending on the GCM and geographic location, predicted leaf area decreased to a point which would no longer sustain loblolly pine forests, and thus indicated a decrease in the southern most range of the species within the region. These results should be evaluated in relation to other changing environmental factors (i.e., CO₂ and O₃) which are not present in the current model.     

POTENTIAL,ACTUAL, AND EQUILIBRIUM EVAPOTRANSPIRATION IN A WHEAT FIELD 1

ABSTRACT: This paper examines the relationship between both potential (E*) and nonpotential evapotranspiration and equilibrium evapotranspiration (EQ) in an irrigated wheat field in southcentral Alberta, Canada. The control exercised by surface wetness and root reservoir moisture content in determining the value of the Priestley-Taylor constant a is explored. Also investigated is the relationship between a and the vapor flux fraction ET/(R-G) where ET is the actual evapotranspiration, R the net radiation, and G the soil heat flux. It is shown that evapotranspiration occurred at the potential rate (E*) when the available soil moisture (ASM) within the root zone was ≥3 percent. a varied from 0.84 for a dry soil to 1.49 for a saturated soil. The mean a for E* was 1.24. Surface wetness sustained evapotranspiration at the potential rate when such wetting exceeded 2mm d^?1 following a period of prolonged drawdown of soil moisture, α and ET/(R-G) were positively correlated and this correlation strengthened with increasing soil moisture for constant values of the energy partitioning factor s+γ/s where s is the slope of the saturation humidity-temperature curve and γ is the psychrometric constant. ET=EQ when ETI(R-G) lay within the range of 0.59 to 0.82 corresponding to Bowen ratio (β) values of 0.22 and 0.69, respectively.     

EVAPOTRANSPIRATION FROM WATER HYACINTH (Eichhomia crassipes (Mart.) Solms) IN TEXAS RESERVOIRS1

ABSTRACT: Water hyacinth, an attractive, floating aquatic plant, poses a substantial threat of unanticipated water loss from Texas reservoirs. A mature plant will lose about three times as much water through evapotranspiration as is lost from evaporation of an equivalent area of open water. The reservoirs of east and southeast Texas, which comprise the bulk of the state's existing and planned water storage capacity, seem likely to suffer a 20 percent average surface infestation of water hyacinth. A coverage that great will result in a yearly net loss of over 2,000,000 acre-feet of impounded water, based on present water development plans for the state. This would amount to nearly 20 percent of the anticipated yield from the reservoirs affected. An effective aquatic plant control program could head off the threat of this significant water loss.     

IMPACTS OF SURFACE DRAINAGE ON GROUND WATER HYDRAULICS1

ABSTRACT: The current dredge and fill practices in locating canals along the periphery of wetlands in south Florida are transforming natural basins that originally had primarily slower subsurface drainage to ones that discharge larger quantities of water faster, via a surface drainage system. The objective of this paper is to develop an analytical technique and a numerical model in quantifying the difference of surface and subsurface runoff before and after the construction of drainage canals, and for delineating the effects of drains on channel level and regional water tables in adjacent areas in south Florida. The surface runoff model is formulated on the climatic water balance technique, and the ground water model is treated as a one dimensional transient phenomenon that forms a nonlinear flow problem. Analytical solutions are derived through problem linearization. These two models are coupled to estimate the impact of drainage canals on the adjacent water table drawdown.     

MODELING ACTUAL EVAPOTRANSPIRATION FROM FORESTED WATERSHEDS ACROSS THE SOUTHEASTERN UNITED STATES1

ABSTRACT: About 50 to 80 percent of precipitation in the southeastern United States returns to the atmosphere by evapotranspiration. As evapotranspiration is a major component in the forest water balances, accurately quantifying it is critical to predicting the effects of forest management and global change on water, sediment, and nutrient yield from forested watersheds. However, direct measurement of forest evapotranspiration on a large basin or a regional scale is not possible. The objectives of this study were to develop an empirical model to estimate long‐term annual actual evapotranspiration (ART) for forested watersheds and to quantify spatial AET patterns across the southeast. A geographic information system (GIS) database including land cover, daily streamflow, and climate was developed using long term experimental and monitoring data from 39 forested watersheds across the region. Using the stepwise selection method implemented in a statistical modeling package, a long term annual AET model was constructed. The final multivariate linear model includes four independent variables—annual precipitation, watershed latitude, watershed elevation, and percentage of forest coverage. The model has an adjusted R² of 0.794 and is sufficient to predict long term annual ART for forested watersheds across the southeastern United States. The model developed by this study may be used to examine the spatial variability of water availability, estimate annual water loss from mesoscale watersheds, and project potential water yield change due to forest cover change.     

A REEVALUATION OF THE GROUND WATER BUDGET FOR LAS VEGAS VALLEY,NEVADA, WITH EMPHASIS ON GROUND WATER DISCHARGE1

ABSTRACT: An essential component to the ground water budget for the Las Vegas Valley (LVV) in southern Nevada is discharge from the ground water system. Discharge for the LW has been based on estimates made more than 50 years ago of 35,524,224 m3 per year as evapotranspiration (ET) and 0 m³ per year as subsurface outflow. Newly published values for recharge based on a more robust data set (70,308,360 m³) indicate a large imbalance associated with the earlier discharge estimates, providing the basis for the reevaluation conducted in this study. ET estimates in this study, as opposed to previous studies, were assigned a range in values that included an approach that assigned higher weight to the unique soil, plant, water, and climatic conditions that existed in predevelopment (1905) LW. The earlier discharge estimates also assumed that the basin was hydrologically closed; however, based on our evaluation, a range in yearly discharge by subsurface outflow from 1,480,176 m³ to 19,735,680 m³ could be assigned. Likewise, a range in yearly ET from 20,475,768 m³ to 78,819,372 m³ could be assigned. Based on newly published recharge values, closure can only occur if higher values are assigned to both the subsurface outflow and/or ET components of ground water discharge. We cannot provide a complete water balance closure with our ground water discharge estimate of 64,140,960 m³. However our reevaluation gives support to the higher recharge estimates and provides the rationale for future studies to be conducted based on a more rigorous scientific assessment.     

论重大危险源监控与重大事故隐患治理

重大危险源是指工业活动中危险物质或能量超过临界量的设备、设施或场所。工业活动中重大火灾、爆炸、毒物泄漏事故 ,尽管其起因和影响不尽相同 ,但都有一个共同的特征 :其根源是存在大量的易燃、易爆、有毒物质或具有引发灾难事故的能量。重大危险源同重大事故隐患是两个既有联系又有区别的概念 ,前者强调设备、设施、场所中存在或固有的危险物质 (能量 )的多少 ,后者则可以认为是出现明显缺陷 (人的不安全行为 ,物的不安全状态或管理上的缺陷 )的重大危险源。从重大事故隐患治理到重大危险源普查 (申报 )、监控是预防重大事故理论与技术的进步 ,是从源头抓预防 ,是落实预防为主 ,关口前移的具体体现 ,也是国家安全生产法律、法规的强制要求。笔者论述了重大危险源监控、重大事故隐患治理与重大事故预防之间的区别与联系 ,用事故是能量意外释放的观点 ,论述了安全是相对的、危险是永存的、事故是可以预防的 ;分析了建立重大危险源监控体系与重大事故预防控制体系的几大要素 ,即危险源辨识、评价、分级管理与监控 ,应急救援等。     

事故与熵──事故发生可能性计算的新方法

从熵增加的观点描述了事故的本质，剖析了人机系统的实质与特性，提出了风险熵与事故势的概念，给出了计算机风险熵与事故势的方法。结果表明，系统具有二重性。在系统运行期间，系统具有封闭体系的特性；在休整期间，系统具有开放体系的特性。事故是运行系统的必然发展趋势，是运行系统的固有属性，是一种自发过程。由于在系统熵增加的过程中信息及能量的交换，可以把事故定义为系统熵增加的结果。避免事故发生的原理是不断地向系统输入信息或负熵以抵消系统内部的熵增加。     

A GEOGRAPHIC INFORMATION SYSTEM TO PREDICT NON-POINT SOURCE POLLUTION POTENTIAL1

ABSTRACT: Bacterial densities (total coliform, fecal coliform, and fecal streptococci) and suspended solids in runoff from a feedlot, pasture, and corn field were measured. Densities of fecal coliform were highest from the feedlot but were 1000 to 10,000 times greater than the water quality standard for swimmable waters from all three land uses. Densities of fecal streptococci were highest from the corn field, which suggests that wildlife are the source of bacteria. Fecal coliform/fecal streptococci ratios distinguished cattle from wildlife as the source of bacterial pollution both among land uses and among seasons of the year. Suspended solids concentrations in runoff ranged from 423 to 925 mg/l and were highest from the corn field. A Geographic Information System (GIS), which utilizes a raster or grid-cell format, was developed to include algorithms associated with non-point source pollution. The system accepts digitally mapped information on soil type, topography, and land use. It calculates characteristics such as slope and slope length, and relates these characteristics to soils and land use parameters in order to produce three dimensional maps of runoff potential, sediment pollution potential, and bacterial pollution potential. It offers the advantages of retaining the geographic character of pollution potential information and of conveying in three-dimensional graphical terms the effects of topography, soil type, land use, and land management practices.     

WATER BALANCE OF PACIFIC ATOLLS1

ABSTRACT: This study presents an estimate of water balance components for Pacific atolls under average dimatological conditions. Figures show annual potential evapotranspiration, annual recharge for rain-fed and aquifer-fed vegetated areas, and the number of months that potential evapotranspiration exceeds actual evapotranspiration (indicating water stress) under average conditions. The method relies on the assumption that small islands have minimal influence on cloudiness and precipitation. The potential evapotranspiration is computed using the equilibrium evaporation concept, and estimates of monthly soil water storage and recharge follow Thornthwaite's bookkeeping method. Gradients in potential evapotranspiration run primarily north-south, though for the equatorial zone potential evapotranspiration declines from east to west, opposing the trend in rainfall. Recharge estimates range from 250 mm in the central Tuamotu Archipelago and zero in eastern Kiribati to over 2000 mm per year in the southern Caroline Islands (U.S. Trust Territory) and Solomon Islands. The sensitivity of the model to intra-month rainfall variability and a range of available soil moisture values is discussed.