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1.
Fitting Drought Duration and Severity with Two-Dimensional Copulas   总被引:20,自引:0,他引:20  
This study aims to model the joint drought duration and severity distribution using two-dimensional copulas. The method of inference function for margins (IFM method) is employed to construct copulas. Two separate maximum likelihood estimations of univariate marginal distributions are performed first, then followed by a maximization of the bivariate likelihood as a function of the dependence parameters. The drought duration and severity are assumed to be exponential and gamma distributions, respectively. Several copulas are tested to determine the best data fitted copula. Droughts, defined using the Standardized Precipitation Index (SPI), of Wushantou (Taiwan) are employed as an example to illustrate the proposed methodology. The copula fitting results for drought duration and severity are quite satisfactory. The bivariate drought analyses, including the joint probabilities and bivariate return periods, based on the derived copula-based joint distribution are also investigated to demonstrate the advantages of bivariate modeling of droughts.  相似文献
2.
The impacts of climate change and human activates on the runoff for Huifa River Basin, Northeast China, have been investigated with the soil and water assessment tool (SWAT), which is calibrated and verified for the baseline period 1956–1964, and then used to reconstruct the natural runoff from 1965 to 2005. The results indicate that both climate change and human activities are responsible for the decrease of observed runoff in Huifa River. The climate change could result in a decrease or increase of runoff depending on precipitation, temperature, radiation variation, as well as land cover changes. Its impacts on annual runoff are -36.7, -59.5, +36.9 and -45.2 mm/a for 1965–1975, 1976–1985, 1986–1995 and 1996–2005, respectively, compared with the baseline period 1956–1964. Human activities, on the other hand, generally lead to a decrease of runoff and a relatively larger magnitude than climate change after 1985. It has decreased the annual runoff by -32.9, -46.8, -67.8 and -54.9 mm/a for 1965–1975, 1976–1985, 1986–1995 and 1996–2005, respectively. Human activities contributed more to runoff decrease in wet years due to regulation and storage of the water projects. The results of this study could be a reference for regional water resources management since there are quite a number of reservoirs in the Huifa River basin.  相似文献
3.
Disposal of sewage sludge is forbidden and agricultural use of stabilized sludge will be banned in 2005 in Switzerland. The sludge has to be dewatered, dried, incinerated and the ashes disposed in landfills. These processes are cost intensive and lead also to the loss of valuable phosphate resources incorporated in the sludge ash. The implementation of processes that could reduce excess sludge production and recycle phosphate is therefore recommended. Partial ozonation of the return sludge of an activated sludge system reduces significantly excess sludge production, improves settling properties of the sludge and reduces bulking and scumming. The solubilized COD will also improve denitrification if the treated sludge is recycled to the anoxic zone. But ozonation will partly inhibit and kill nitrifiers and might therefore lead to a decrease of the effective solid retention time of the nitrifier, which reduces the safety of the nitrification. This paper discusses the effect of ozonation on sludge reduction, the operation stability of nitrification, improvement of denitrification and gives also an energy and cost evaluation.  相似文献
4.
Fifty years ago when only BOD was removed at municipal WWTPs primary clarifiers were designed with 2-3 hours hydraulic retention time (HRT). This changed with the introduction of nitrogen removal in activated sludge treatment that needed more BOD for denitrification. The HRT of primary clarification was reduced to less than one hour for dry weather flow with the consequence that secondary sludge had to be separately thickened and biogas production was reduced. Only recently the ammonia rich digester liquid (15-20% of the inlet ammonia load) could be treated with the very economic autotrophic nitritation/anammox process requiring half of the aeration energy and no organic carbon source compared to nitrification and heterotrophic denitrification. With the introduction of this new innovative digester liquid treatment the situation reverts, allowing us to increase HRT of the primary clarifier to improve biogas production and reduce aeration energy for BOD removal and nitrification at similar overall N-removal.  相似文献
5.
Remote sensing (RS) and geographic information system (GIS) are promising tools for efficient planning and management of vital groundwater resources, especially in data-scarce developing nations. In this study, a standard methodology is proposed to delineate groundwater potential zones using integrated RS, GIS and multi-criteria decision making (MCDM) techniques. The developed methodology is demonstrated by a case study in Udaipur district of Rajasthan, western India. Initially, ten thematic layers, viz., topographic elevation, land slope, geomorphology, geology, soil, pre- and post-monsoon groundwater depths, annual net recharge, annual rainfall, and proximity to surface water bodies were considered in this study. These thematic layers were scrutinized by principal component analysis technique to select influential layers for groundwater prospecting. Selected seven thematic layers and their features were assigned suitable weights on the Saaty’s scale according to their relative importance in groundwater occurrence. The assigned weights of the thematic layers and their features were then normalized by using AHP (analytic hierarchy process) MCDM technique and eigenvector method. Finally, the selected thematic maps were integrated by weighted linear combination method in a GIS environment to generate a groundwater potential map. Thus, four groundwater potential zones were identified and demarcated in the study area, viz., ‘good’, ‘moderate’, ‘poor’ and ‘very poor’ based on groundwater potential index values. The area falling in the ‘good’ zone is about 2,113 km2 (17% of the total study area), which encompasses major portions of Sarada, Salumber, Girwa, Dhariawad, and Mavli blocks of the study area. The northeast and southwest portions along with some scattered patches fall in the ‘moderate’ zone, which encompasses an area of 3,710 km2 (about 29%). The ‘poor’ zone is dominant in the study area which covers an area of 4,599 km2 (36% of the total area). The western portion and parts of eastern and southeast portions of the study area are characterized as having ‘very poor’ groundwater potential, and this zone covers an area of 2,273 km2 (18%). Moreover, in the ‘good’ zone, the mean annually exploitable groundwater reserve is estimated at 0.026 million cubic metres per km2 (MCM/km2), whereas it is 0.024 MCM/km2 in the ‘moderate’ zone, 0.018 MCM/km2 in the ‘poor’ zone, and 0.013 MCM/km2 in the ‘very poor’ zone. The groundwater potential map was finally verified using the well yield data of 39 pumping wells, and the result was found satisfactory.  相似文献
6.
Municipal wastewater samples have been collected in three different types of community and fingerprinted by optical methods combining UV-visible spectrometry, synchronous fluorescence spectrometry and turbidity. Correlations, whose slope depends on the sampling location, were obtained between absorbance at 254 nm and the synchronous fluorescence intensity of peaks P1 (I366/316), P2 (I430/380) and P3 (I520/470). The corresponding correlation coefficients are larger than 0.75. Although related to urine as ammonia, the fluorescence intensity of P1 does not exhibit a strong correlation with this substance (correlation coefficient of approximately 0.6). All the measured parameters exhibit diurnal variation patterns related to human activities.  相似文献
7.
Evapotranspiration and evaporation measurements are important parameters for many agricultural activities such as water resource management and environmental studies. There are several models which can determine pan coefficient (K Pan), using wind speed, relative humidity and fetch length conditions. This paper analyses seven exiting pan models to estimate K Pan values for two different climates of Iran. Monthly mean reference crop evapotranspiration (ET0) was calculated according to the pan-ET0 model. The results showed that estimated pan coefficients by majority of the suggested models were not statistically accurate to be used in the pan-ET0 conversion method. However, for the cold semi-arid climate condition, the best K Pan models for estimation of ET0 were Orang and Raghuwanshi–Wallender, respectively. Also, the Snyder and Orang models were best fitted models for warm arid climate, respectively. The mean annual value of K Pan, determined by Penman–Monteith FAO 56 (PMF-56) standard model for warm arid sites, was approximately 32% higher than the corresponding value in the cold semi-arid climate. Similarly, the mean annual ET0 in the warm arid sites was 66% higher, compared to the ET0 of the cold semi-arid sites. These types of warm arid and semi-arid climates are found widely throughout the world.  相似文献
8.
In the present study, soil erosion assessment of Dikrong river basin of Arunachal Pradesh (India) was carried out. The river basin was divided into 200 × 200 m grid cells. The Arc Info 7.2 GIS software and RS (ERDAS IMAGINE 8.4 image processing software) provided spatial input data and the USLE was used to predict the spatial distribution of the average annual soil loss on grid basis. The average rainfall erositivity factor (R) for Dikrong river basin was found to be 1,894.6 MJ mm ha−1 h−1 year−1. The soil erodibility factor (K) with a magnitude of 0.055 t ha h ha−1 MJ−1 mm−1 is the highest, with 0.039 t ha h ha−1 MJ−1 mm−1 is the least for the watershed. The highest and lowest value of slope length factor (LS) is 53.5 and 5.39 respectively for the watershed. The highest and lowest values of crop management factor (C) were found out to be 0.004 and 1.0 respectively for the watershed. The highest and lowest value of conservation factor (P) were found to be 1 and 0.28 respectively for the watershed. The average annual soil loss of the Dikrong river basin is 51 t ha−1 year−1. About 25.61% of the watershed area is found out to be under slight erosion class. Areas covered by moderate, high, very high, severe and very severe erosion potential zones are 26.51%, 17.87%, 13.74%, 2.39% and 13.88% respectively. Therefore, these areas need immediate attention from soil conservation point of view.  相似文献
9.
The COST/IWA benchmark simulation model has been available for seven years. Its primary purpose has been to create a platform for control strategy benchmarking of activated sludge processes. The fact that the benchmark has resulted in more than 100 publications, not only in Europe but also worldwide, demonstrates the interest in such a tool within the research community In this paper, an extension of the benchmark simulation model no 1 (BSM1) is proposed. This extension aims at facilitating control strategy development and performance evaluation at a plant-wide level and, consequently, includes both pre-treatment of wastewater as well as the processes describing sludge treatment. The motivation for the extension is the increasing interest and need to operate and control wastewater treatment systems not only at an individual process level but also on a plant-wide basis. To facilitate the changes, the evaluation period has been extended to one year. A prolonged evaluation period allows for long-term control strategies to be assessed and enables the use of control handles that cannot be evaluated in a realistic fashion in the one-week BSM1 evaluation period. In the paper, the extended plant layout is proposed and the new suggested process models are described briefly. Models for influent file design, the benchmarking procedure and the evaluation criteria are also discussed. And finally, some important remaining topics, for which consensus is required, are identified.  相似文献
10.
Delineation of Flood-Prone Areas Using Remote Sensing Techniques   总被引:7,自引:1,他引:6  
Flood problems resulting due to heavy rainfall and drainage congestion are being regularly experienced in plain areas of Bihar, India. Due to this problem, power plant located in Koa catchment, Kahalgaon, Bihar, is faces huge loss at the time of flood. In this paper, the flood-affected areas in Koa catchment have been mapped using remote sensing satellite data (IRS LISS III, 1999 and Landsat TM, 1995). A range of image processing techniques has been used, including simple density slicing, Tasseled Cap Transformation and water-specific index. The results obtained using different approaches have been analysed. Result indicates that a Normalized Difference Water Index (NDWI) based approach produced best results.  相似文献
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