Evaporation from Lake Superior: 1. Physical controls and processes

The surface energy balance of Lake Superior was measured using the eddy covariance method at a remote, offshore site at 0.5-h intervals from June 2008 through November 2010. Pronounced seasonal patterns in the surface energy balance were observed, with a five-month delay between maximum summer net radiation and maximum winter latent and sensible heat fluxes. Late season (winter) evaporation and sensible heat losses from the lake typically occurred in two- to three-day-long events, and were associated with significant release of stored heat from the lake. The majority of the evaporative heat loss (70-88%) and sensible heat loss (97-99%) occurred between October and March, with 464 mm (2008-2009) and 645 mm (2009-2010) of evaporative water loss occurring over the water year starting October 1. Evaporation was proportional to the horizontal wind speed, inversely proportional to the ambient vapor pressure, and was well described by the ratio of wind speed to vapor pressure. This ratio remained relatively constant between the two water years, so the differences in evaporative water loss between years were largely associated with differences in lake surface conditions (e.g. water temperature, ice cover, and ice duration). Since late-season water temperature decline is driven by evaporative and sensible heat loss, the potential for a negative feedback mechanism between evaporation and ice cover is discussed.     

南宁站蒸发皿蒸发变化特性及成因分析

基于南宁气象站1954-2012年气象数据,采用距平法、Mann-Kendall检验法、突变分析法及相关分析法等方法分析了蒸发皿蒸发的变化趋势以及蒸发皿蒸发与其他气象要素（降水、气温、日照时数、风速、相对湿度等）的相关性,识别影响蒸发皿蒸发变化的主导因素。结果表明：1954-2001年期间,蒸发皿蒸发主要呈现下降趋势;日照时数与蒸发皿蒸发的相关性最高,其次为风速和相对湿度,说明影响南宁站蒸发皿蒸发变化的主要因素是日照时数、风速及相对湿度。     

Modeling Evaporation-Seepage Losses for Reservoir Water Balance in Semi-arid Regions

In the water balance of reservoir system, evaporation plays a crucial role particularly so for the reservoir systems of smaller size located in the semi-arid or arid regions. Such regions are most often characterized by significant seepage losses from reservoirs, besides evaporation losses. Usually, in the optimization of a reservoir system, it is a common practice to assume evaporation loss either as some constant value or as negligible. Such assumptions, however, may affect the results of reservoir optimization. This is demonstrated in this study by a case study in the optimal scheduling of Pilavakkal reservoir system in Vaipar basin of Tamilnadu, India. For modeling reservoir losses, many models are available, of which, Penman combination model is most commonly used. In this study, an alternative approach based on Genetic Programming (GP) is proposed. The results of GP and Penman model for both evaporation loss estimation and reservoir scheduling are compared. It is found that while GP and Penman combination model performs equally well for estimating evaporation losses, GP is also able to model seepage losses (or other losses from reservoir) to a much better degree. It is also shown the reservoir scheduling does get influenced based on how the reservoir losses are modeled in the reservoir water balance equation.     

Understanding groundwater table using a statistical model

In this study, a statistical model was established to estimate the groundwater table using precipitation, evaporation, the river stage of the Liangduo River, and the tide level of the Yellow Sea, as well as to predict the groundwater table with easily measurable climate data in a coastal plain in eastern China. To achieve these objectives, groundwater table data from twelve wells in a farmland covering an area of 50 m × 150 m were measured over a 12-month period in 2013 in Dongtai City, Jiangsu Province. Trend analysis and correlation analysis were conducted to study the patterns of changes in the groundwater table. In addition, a linear regression model was established and regression analysis was conducted to understand the relationships between precipitation, evaporation, river stage, tide level, and groundwater table. The results are as follows:(1) The groundwater table was strongly affected by climate factors(e.g., precipitation and evaporation), and river stage was also a significant factor affecting the groundwater table in the study area( p 0.01, where p is the probability value).(2) The groundwater table was especially sensitive to precipitation. The significance of the factors of the groundwater table were ranked in the following descending order:precipitation, evaporation, and river stage.(3) A triple linear regression model of the groundwater table, precipitation, evaporation, and river stage was established. The linear relationship between the groundwater table and the main factors was satisfied by the actual values versus the simulated values of the groundwater table(R~2 = 0.841, where R~2 is the coefficient of determination).     

The utility of thermal satellite images and land-based meteorology to estimate evaporation from large lakes

Evaporation measurements over lakes are limited by physical constraints, logistics and financial demands. Thermal satellite images and land-based meteorology can be combined to derive evaporation rates from large lakes. The Dead Sea is a large hypersaline lake that can be used to examine the utility of thermal satellite images along with land-based meteorology to assess evaporation rates. Sea surface tmperature was retrieved for a 12-month period using band 10 onboard Landsat 8. Monthly SST was combined with nearby land-based meteorology to estimate evaporation from the sea surface using a mass transfer method and two variations of the Penman procedure. The Mass transfer gave an annual evaporation rate of 1005 mm whereas the Penman and the Priestley-Taylor methods gave 1308 and 1140 mm, respectively. These values are commensurate with extensive field measurement and theoretically derived evaporation values. Analysis shows a tradeoff between wind speed increase over the smoother lake surface and the drop in the saturation water vapor pressure deficit across the lake-atmosphere boundary. Wind speed has profound effects on evaporation differences during the warm season but diminish appreciably in the cold season when the vapor pressure deficit is small. Thermal images were able to resolve the presence of large pockets of cool water over the Dead Sea resulting from freshwater input. Modifications to evaporation caused by freshwater input to a hypersaline lake are investigated from a thermodynamic perspective. The alteration to evaporation depends on the simultaneous departure of surface temperature and the activity of the brine.     

Evaporation from Lake Superior: 2: Spatial distribution and variability

Evaporation is a critical component of the water balance of each of the Laurentian Great Lakes, and it is expected that because of their shear size, evaporation cannot be spatially or temporally uniform. Despite this, examples of spatially distributed estimates of evaporation in the scientific literature are rare for most of the lakes and non-existent for Lake Superior. Direct measurements of evaporation taken at an offshore site on Lake Superior from June 2008 to October 2010 were used with concurrent satellite and climate model data to extrapolate evaporation measurements across the entire lake. Evaporation rates, large scale forcing mechanisms, and spatial patterns and variability are presented. Spatial patterns of evaporation tend to follow synoptic-scale air masses traveling over the lake. While most evaporation occurs during relatively short term events, these episodes tend not to occur in isolated locations on the lake, but are spatially widespread. The exceptions to this rule are during periods of a stable atmosphere and low evaporation, and when a transient ice cover can limit evaporation from some areas.     

给水度概念和广义给水度变化规律的初步分析

本文首先讨论了给水度的概念,区分于重力给水度和广义给水度两种定义,然后通过数值模拟计算探讨了地下水位匀速下降条件下,层状非均质多孔介质广义给水度的变化规律。     

Temporal variations of reference evapotranspiration and its sensitivity to meteorological factors in Heihe River Basin,China

On the basis of daily meteorological data from 15 meteorological stations in the Heihe River Basin(HRB) during the period from 1959 to 2012, long-term trends of reference evapotranspiration(ET0) and key meteorological factors that affect ET0 were analyzed using the MannKendall test. The evaporation paradox was also investigated at 15 meteorological stations. In order to explore the contribution of key meteorological factors to the temporal variation of ET0, a sensitivity coefficient method was employed in this study. The results show that:(1) mean annual air temperature significantly increased at all 15 meteorological stations, while the mean annual ET0 decreased at most of sites;(2) the evaporation paradox did exist in the HRB, while the evaporation paradox was not continuous in space and time; and(3) relative humidity was the most sensitive meteorological factor with regard to the temporal variation of ET0 in the HRB, followed by wind speed, air temperature, and solar radiation. Air temperature and solar radiation contributed most to the temporal variation of ET0 in the upper reaches; solar radiation and wind speed were the determining factors for the temporal variation of ET0 in the middle-lower reaches.     

Cities and environment in the twenty-first century: A future-oriented synthesis after Habitat II

A gigantic urban revolution is under way today: in 40 years, the equivalent of 1000 cities, each of three million inhabitants, will have to be built. In 2005, half of the world's population will live in cities. This growth will be concentrated in major cities, most of them in the South. This article reviews some fundamental trends, challenges and possible solutions in environment-related fields such as water, transports, energy. It argues for the emergence of a new urban culture based on the adoption of sustainable urban consumption patterns, new urban partnerships and the strengthening of urban solidarities. It gives examples of practical solutions within our reach for humanizing cities in the 21st century.     

SZS 20-1.25-Q型燃气锅炉测试分析与技术改造

SZS20-1．25-Q型燃气锅炉由于蒸发量不足，长期不能满负荷运行，不能安全运行。通过对锅炉测试数据进行分析计算，找到了锅炉系统的设计缺陷，采用微正压平衡通风等技术改造措施，经过热工测试对比，表明技术措施取得了较好的效果，保证了该型锅炉的供热能力和安全运行。