REVISITING THE DEGREE-DAY METHOD FOR SNOWMELT COMPUTATIONS1

ABSTRACT: The simple, empirical degree-day approach for calculating snowmelt and runoff from mountain basins has been in use for more than 60 years. It is frequently suggested that the degree-day method be replaced by the more physically-based energy balance approach. The degree-day approach, however, maintains its popularity, applicability, and effectiveness. It is shown that the degree-day method is reliable for computing total snowmelt depths for periods of a week to the entire snowmelt season. It can also be used for daily snowmelt depths when utilized in connection with an adequate snowmelt runoff model for computing the basin runoff. The degree-day ratio is shown to vary seasonally as opposed to being constant as is often assumed. Additionally, in order to evaluate the degree-day ratio correctly, the changing snow cover extent in a basin during the snowmelt season must be taken into account. It is also possible to combine the degree-day approach with a radiation component so that short time interval (<24 hours) computations of snowmelt depth can be made. When snowmelt input is transformed to basin output (runoff) by a snowmelt runoff model, there is little difference between the degree-day approach and a radiation-based approach. This is fortuitous because the physically-based energy balance models will not soon displace the degree-day methods because of their excessive data requirements.     

二维定常泥流的数值模拟

本文以Ｎａｖｉｅｒ－Ｓｔａｋｅｓ方程为基本方程，将泥石流的一种特殊形式－泥流作为Ｂｉｎｇｈａｍ流体，用有限体积法对三种不同底部条件的泥流流场进行了数值模拟，给出了速率分布，并指出了泥流与清水流动的不同之处。     

FIELD TESTING OF AN ICE-PRESERVING WINTER LAKE AERATION SYSTEM1

ABSTRACT: Artificial aeration is used to prevent winter fish kills due to oxygen depletion in ice-covered lakes. Conventional aeration by air bubble plumes and other techniques usually mixes the water column and produces hazardous open water in the ice cover. A non-mixing winter lake aeration system which creates a fish refuge was designed and field tested to oxygenate the water and maintain water temperature stratification in a lake such that no open water is created. The system uses a cascade aerator and has a design discharge and dissolved oxygen input rate of 85 1/s and 70 kg/d, respectively. Aerated water is discharged near mid-depth with minimum disturbance of the ambient water through a specially designed diffuser. The system was tested in a shallow 3 m deep lake of 17 ha surface area during two winters and was found to perform as expected. Significant photosynthetic production of dissolved oxygen under the ice-cover was also observed during snow-free periods.     

Mitochondrial DNA variation pattern and postglacial history of the Siberian larch (<Emphasis Type="Italic">Larix sibirica</Emphasis> Ledeb.)

Mitochondrial DNA (mtDNA) variation has been studied in populations of the Siberian larch with the use of five PCR-based markers characterizing 29 haplotypes. The studied populations from the main parts of the Siberian larch range belong to several geographically isolated groups with their specific sets of haplotypes, which have probably originated from separate refugia for forest vegetation of the last glacial maximum. Conclusions concerning the possible location of these refugia and the ways and pattern of the postglacial recolonization of the recent Siberian larch range are drawn. The spatial distribution of haplotypes within individual populations is nonrandom. The typical size of the area occupied by a group of plants with the same haplotype is 50–100 m across.     

Current Practices and Future Opportunities for Policy on Climate Change and Invasive Species

Abstract:  Climate change and invasive species are often treated as important, but independent, issues. Nevertheless, they have strong connections: changes in climate and societal responses to climate change may exacerbate the impacts of invasive species, whereas invasive species may affect the magnitude, rate, and impact of climate change. We argue that the design and implementation of climate-change policy in the United States should specifically consider the implications for invasive species; conversely, invasive-species policy should address consequences for climate change. The development of such policies should be based on (1) characterization of interactions between invasive species and climate change, (2) identification of areas where climate-change policies could negatively affect invasive-species management, and (3) identification of areas where policies could benefit from synergies between climate change and invasive-species management.     

武钢四烧除尘系统风量平衡调试

武钢四烧除尘系统存在着吸尘点冒灰、管道堵塞、磨损等问题,严重影响除尘系统的正常运行。通过风量平衡调试及采取有效的整改措施,上述问题得到了较彻底的解决。