Simulating land use for protecting food crop areas in northeast Thailand using GIS and Dyna-CLUE     

Sakayarote  Kanda  Shrestha  Rajendra P. 《地理学报(英文版)》2019,29(5):803-817

Journal of Geographical Sciences - Land use in the northeast region of Thailand has changed dramatically in the past two decades. These changes are mainly due to the government policies, which...  相似文献   

Land fragmentation due to rapid urbanization in the Phoenix Metropolitan Area: Analyzing the spatiotemporal patterns and drivers   总被引：4，自引：0，他引：4  

Milan K. Shrestha  Abigail M. YorkChristopher G. Boone  Sainan Zhang 《Applied geography (Sevenoaks, England)》2012,32(2):522-531

Rapid urbanization of the Phoenix Metropolitan Area exemplifies the dominant US Southwest urban growth pattern of the past six decades. Using a combination of multitemporal land cover data, gradient analysis, and landscape metrics, we quantify and characterize spatiotemporal patterns of land fragmentation observed in Phoenix. We analyze historical, qualitative data to identify five major socio-ecological drivers critical to understanding the urbanization processes and fragmentation patterns: population dynamics, water provisioning, technology and transportation, institutional factors, and topography. A second objective is to assess the applicability and accuracy of National Land cover Database (NLCD)-—a widely used land cover dataset—-to detect and measure urban growth and land fragmentation patterns in the relatively treeless desert biome of the US Southwest. In contrast to studies in the temperate eastern USA where NLCD has proved inaccurate for detection of exurban development, our study demonstrates that NLCD is a reliable data source for measuring land use in the southwest, even in low-density environments. By combining qualitative analyses of social-ecological drivers with fragmentation analyses, we move toward an improved understanding of urbanization and insights on the human modification framework used widely in land change science.  相似文献   

Instance‐based learning compared to other data‐driven methods in hydrological forecasting     

Dimitri P. Solomatine  Mahesh Maskey  Durga Lal Shrestha 《水文研究》2008,22(2):275-287

Data‐driven techniques based on machine learning algorithms are becoming popular in hydrological modelling, in particular for forecasting. Artificial neural networks (ANNs) are often the first choice. The so‐called instance‐based learning (IBL) has received relatively little attention, and the present paper explores the applicability of these methods in the field of hydrological forecasting. Their performance is compared with that of ANNs, M5 model trees and conceptual hydrological models. Four short‐term flow forecasting problems were solved for two catchments. Results showed that the IBL methods often produce better results than ANNs and M5 model trees, especially if used with the Gaussian kernel function. The study showed that IBL is an effective data‐driven method that can be successfully used in hydrological forecasting. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Improved visibility calculations with tree trunk obstruction modeling from aerial LiDAR     

Jayson J. Murgoitio  Rupesh Shrestha  Lucas P. Spaete 《International journal of geographical information science》2013,27(10):1865-1883

Viewshed and line-of-sight are spatial analysis functions used in applications ranging from urban design to archaeology to hydrology. Vegetation data, a difficult variable to effectively emulate in computer models, is typically omitted from visibility calculations or unrealistically simulated. In visibility analyzes performed on a small scale, where calculation distances are a few hundred meters or less, ineffective incorporation of vegetation can lead to significant modeling error. Using an aerial LiDAR (light detection and ranging) data set of a lodgepole pine (Pinus contorta) dominant ecosystem in Idaho, USA, tree obstruction metrics were derived and integrated into a short-range visibility model. A total of 15 visibility plots were set at a micro-scale level, with visibility modeled to a maximum of 50 m from an observation point. Digital photographs of a 1 m² target set at 5 m increments along three sightline paths for each visibility plot were used to establish control visibility values. Trunk obstructions, derived from mean vegetation height LiDAR data and processed through a series of tree structure algorithms, were factored into visibility calculations and compared to reference data. Results indicate the model calculated using trunk obstructions with LiDAR demonstrated a mean error of 8.8% underestimation of target visibility, while alternative methods using mean vegetation height and bare-earth models have an underestimation of 65.7% and overestimation of 31.1%, respectively.  相似文献   

Investigations on different positions of electrodes and their effects on the distribution of Cr at the water sediment interface     

R. Shrestha M. Phil. Ph.D.  R. Fischer Ph.D.  M. Sillanpää D.Sc. 《International Journal of Environmental Science and Technology》2007,4(4):413-420

In most mining areas, significant concentrations of metals such as Pb, Cu, Cr, Zn, Cd, Fe, Mn, Co, Ni, Hg, Ar, halogenated organic compounds and radionuclides are found. Of those, Cr is one of the well-known heavy metals that forms toxic species. It is necessary to study the mobilization and accumulation of Cr at the sediment water interface in an electric field at varying different positions and conditions of the electrode arrangement. The tests were carried out with a natural sediment containing heavy metals from the river Weisse Elster (Germany). The electrokinetic experiments have been performed in columns filled with sediment using electrodes made of conductive polymers (polyethylene with carbon black) at a maximum current density of 0.5 mA/cm². The experimental results suggest that the mobilization and accumulation of Cr highly depends on chemical factors for e.g., pH value, redox potential, respectively redox status and the content of Fe, A1 and organic matter in the soil or sediment. The sorption of Cr (III, VI) is very high in the pH range > 4.5. As expected, a high mobilization of Cr (III, VI) was seen in the case of the experiments with the anode at the sediment, because the pH value was lower than mentioned above. On the opposite, the best conditions for the Cr (III, VI) immobilization is high pH values (cathode at the sediment).  相似文献   

Shallow groundwater in a middle mountain catchment of Nepal: quantity and quality issues   总被引：1，自引：0，他引：1  

Bhawani S. Dongol  Juerg Merz  Monika Schaffner  Gopal Nakarmi  Pravakar B. Shah  Smita K. Shrestha  Pradeep M. Dangol  Madhav P. Dhakal 《Environmental Geology》2005,49(2):219-229

The use of shallow groundwater in middle mountain catchments of Nepal is a recent development. It was only in early 1998 that a number of dug wells had been constructed in the Jhikhu Khola catchment. But their numbers are rapidly increasing. While it seems to be a good way of accessing additional water resources both for domestic (current) and agricultural purposes (future), it is very important that the groundwater resources are not overexploited. Current dug wells are used to abstract groundwater, which is seasonally being recharged by the abundant monsoon rainfall. The water levels responded rapidly to the rainfall and differed according to the location of the well. The water quality parameters indicated that the water of most of the wells was not suitable for drinking purposes without prior treatment. Microbiological contamination is of particular concern, in addition to the high nitrate and phosphate levels. Some wells show elevated turbidity levels, indicating that there is an interaction between the muddy surface water and the water in the well.  相似文献   

Rain Erosion Hazard Evaluated from Microtopographic Erosion Features on Arable Fields and Forest: A Case Study in Nepal     

Lok Bahadur Kunwar  Eelko Bergsma  Drubha Pikha Shrestha 《Geografiska Annaler: Series A, Physical Geography》2003,85(3-4):313-321

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Ecopolitical battles at the Tarai frontier of Nepal: an emerging human and environmental crisis     

Shrestha NR  Conway D 《International journal of population geography : IJPG》1996,2(4):313-331

"In Nepal, the drama of human and environmental ills is increasingly being played out in the form of peasants' ecopolitical battles over common land access and control, such as in the Tarai frontier, a region bordering the Gangetic Plain of India. This is a complex battle, pitting peasants' day-to-day survival against environmental security on one front, and against the Nepalese State and its dominant class interests on the other. This article critically dissects this raging battle to gain a clear understanding of its complexities as well as its diverse roots."  相似文献   

Contaminant Movement Under Pumpage-Recharge Condition in Steady Ground-Water Flow System     

A. Das Gupta  P. R. Onta Shrestha 《Ground water》1986,24(3):342-350

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Diurnal and seasonal variations of meteorology and aerosol concentrations in the foothills of the nepal himalayas (Nagarkot: 1,900 m asl)     

Rudra K. Shrestha  Martin W. Gallagher  Paul J. Connolly 《Asia-Pacific Journal of Atmospheric Sciences》2016,52(1):63-75

A 10-months long monitoring experiment to investigate the diurnal and seasonal variation of aerosol size distribution at Nagarkot (1,900 m asl) in the Kathmadu Valley was carried out as part of a study on katabatic and anabatic influence on pollution dispersion mechanisms. Seasonal means show total aerosol number concentration was highest during post-monsoon season (775 ± 417 cm^?3) followed by pre-monsoon (644 ± 429 cm^?3) and monsoon (293 ± 205 cm^?3) periods. Fine particle concentration (0.25 μm ≤ D_P ≤ 2.5 μm) dominated in all seasons, however, contribution by coarse particles (3.0 μm ≤ D_P ≤ 10.0 μm) is more significant in the monsoon season with contributions from particles larger than 10.0 μm being negligible. Our results show a regular diurnal pattern of aerosol concentration in the valley with a morning and an evening peak. The daily twin peaks are attributed to calm conditions followed by transitional growth and break down of the valley boundary layer below. The peaks are generally associated with enhancement of the coarse particle fraction. The evening peak is generally higher than the morning peak, and is caused by fresh evening pollution from the valley associated with increased local activities coupled with recirculation of these trapped pollutants. Relatively clean air masses from neighbouring valleys contribute to the smaller morning peak. Gap flows through the western passes of the Kathmandu Valley, which sweep away the valley pollutants towards the eastern passes modulated by the mountain - valley wind system, are mainly responsible for the dominant pollutant circulation patterns exhibited within the valley.  相似文献