Short-Term Evaporation Estimating From Complex Small Lakes In Arid And Semi-Arid Regions

In many parts of the world, the available water resources are now being used close to their limits. Global climate change, the increasing population of the earth and ever-increasing standards of living and consequent growing demand of water are bringing water sustainability into sharp focus. Evaporation as a major component of the hydrologic cycle, is the largest one of water loss from lakes especially in arid and semi-arid regions. Because of lacking of understanding of the thermodynamics of atmospheric boundary layer(ABL) and heat exchange between the water surface and atmosphere, an accurate estimation of evaporation from water surfaces is almost unknown. It is thus of major importance to have precise estimation of the amount of this undesirable, unrecoverable and unproductive water loss from water body for a good management of available water resources. However, most of the models so far described in the literature are one-dimensional with areal homogeneity assumption and can be used for long-term estimations. In the framework of this study, a numerical approach was developed to predict evaporation from shallow and small lakes in (semi-) arid regions considering the heat and water vapor exchanges process between the air-water surface . The model takes into account advection, oasis effect and stability conditions of ABL in the heat exchange process. To have a precise estimation of evaporation the effects of the terrain surrounding the water body, the water body size and the effects of the available fetch of water body were implemented in the model. The governing equations of the model have been solved by OpenFOAM ; an open source, freely available CFD toolbox and easily extended to run in parallel. The estimated evaporation values were compared against the field measurements and they showed reasonable agreement

Stormwater quality characteristics in (Dutch) urban areas and performance of settlement basins

Stormwaters, flowing into storm sewers, are known to significantly increase the annual pollutant loads entering urban receiving waters and this results in significant degradation of the receiving water quality. Knowledge of the characteristics of stormwater pollution enables urban planners to incorporate the most appropriate stormwater management strategies to mitigate the effects of stormwater pollution on downstream receiving waters. This requires detailed information on stormwater quality, such as pollutant types, sediment particle size distributions, and how soluble pollutants and heavy metals attach themselves to sediment particles. This study monitored stormwater pollution levels at over 150 locations throughout the Netherlands. The monitoring has been ongoing for nearly 15 years and a total of 7,652 individual events have been monitored to date. This makes the database the largest stormwater quality database in Europe. The study compared the results to those presented in contemporary international stormwater quality research literature. The study found that the pollution levels at many of the Dutch test sites did not meet the requirements of the European Water Framework Directive (WFD) and Dutch Water Quality Standards. Results of the study are presented and recommendations are made on how to improve water quality with the implementation of Sustainable Urban Drainage Systems (SUDS) devices

Temperature Dynamics Investigation At Small And Shallow Lakes Using Hydrodynamic Model

A three-dimensional time-dependent hydrodynamic and heat transport model of Lake Binaba, a shallow and small dam reservoir in Ghana, emphasizing the simulation of dynamics and thermal structure has been developed. Most numerical studies of temperature dynamics in reservoirs are based on one- or two-dimensional models. These models are not applicable for reservoirs characterized with complex flow pattern and unsteady heat exchange between the atmosphere and water surface. Continuity, momentum and temperature transport equations have been solved. Proper assignment of boundary conditions, especially surface heat fluxes, has been found crucial in simulating the lake’s hydrothermal dynamics. This model is based on the Reynolds Average Navier-Stokes equations, using a Boussinesq approach, with a standard k − ε turbulence closure to solve the flow field. The thermal model includes a heat source term, which takes into account the short wave radiation and also heat convection at the free surface, which is function of air temperatures, wind velocity and stability conditions of atmospheric boundary layer over the water surface. The governing equations of the model have been solved by OpenFOAM; an open source, freely available CFD toolbox. As its core, OpenFOAM has a set of efficient C++ modules that are used to build solvers. It uses collocated, polyhedral numerics that can be applied on unstructured meshes and can be easily extended to run in parallel. A new solver has been developed to solve the hydrothermal model of lake. The simulated temperature was compared against a 15 days field data set. Simulated and measured temperature profiles in the probe locations show reasonable agreement. The model might be able to compute total heat storage of water bodies to estimate evaporation from water surface

Do green roofs cool the air?

AbstractRapid urbanization and an increasing number and duration of heat waves poses a need to mitigate extremely high temperatures. One of the repeatedly suggested measures to moderate the so called urban heat island are green roofs. This study investigates several extensive sedum-covered green roofs in Utrecht (NL) and their effect on air temperature right above the roof surface. The air temperature was measured 15 and 30 cm above the roof surface and also in the substrate. We showed that under well-watered conditions, the air above the green roof, compared to the white gravel roof, was colder at night and warmer during the day. This suggests that extensive sedum-covered green roofs might help decrease air temperatures at night, when the urban heat island is strongest, but possibly contribute to high daytime temperatures. The average 24 h effect of sedum-covered green roof was a 0.2 °C increase of air temperature 15 cm above the ground. During a dry year the examined green roof exhibited behavior similar to conventional white gravel roof even exhibited slight cooling effect in late afternoon. Interestingly, the pattern of soil temperature remained almost the same for both dry and well-prospering green roofs, colder during the day and warmer at night

Volta basin water balance

Water balances pertaining to the flux of water through the Volta River Basin and a black box model of the rainfall/runoff relationship for estimating the river flows into the Akosombo Reservoir are presented. As the water demand has approached supply, the tradeoffs between competing water uses are likely to intensify. It is also apparent from the balances that land use and land cover changes in the uplands of the basin are destined to play a pivotal role in determining the future of the basin

An information-theoretical perspective on weighted ensemble forecasts

This paper presents an information--theoretical method for weighting ensemble forecasts with new information. Weighted ensemble forecasts can be used to adjust the distribution that an existing ensemble of time series represents, without modifying the values in the ensemble itself. The weighting can, for example, add new seasonal forecast information in an existing ensemble of historically measured time series that represents climatic uncertainty. A recent article in this journal compared several methods to determine the weights for the ensemble members and introduced the pdf-ratio method. In this article, a new method, the minimum relative entropy update (MRE-update), is presented. Based on the principle of minimum discrimination information, an extension of the principle of maximum entropy (POME), the method ensures that no more information is added to the ensemble than is present in the forecast. This is achieved by minimizing relative entropy, with the forecast information imposed as constraints. From this same perspective, an information--theoretical view on the various weighting methods is presented. The MRE-update is compared with the existing methods and the parallels with the pdf-ratio method are analysed. The paper provides a new, information--theoretical justification for one version of the pdf-ratio method that turns out to be equivalent to the MRE-update. All other methods result in sets of ensemble weights that, seen from the information--theoretical perspective, add either too little or too much (i.e. fictitious) information to the ensemble

Un réseau d'observation climatique intelligente couvrant toute l'Afrique

Les stations d'observation climatique et météorologique sont encore trop peu nombreuses en Afrique, alors que la production alimentaire, les prévisions quant aux récoles et l'atténuation du risque de catastrophe pourraient bénéficier d'une observation améliorée. Un nouveau réseau d'observation climatique et météorologique intelligente et à long terme s'emploie à présent à relever le défi clé de la surveillance météorologique sur le continent