Atmospheric rivers (ARs) are narrow, elongated corridors of high water vapor content transported from tropical and/or extratropical cyclones. We characterize precipitation and snow water equivalent associated with ARs intersecting the western U.S. coast during the cold season (November– March) of water years 1949–2015. For each AR landfalling date, we retrieved the precipitation and relevant hydrometeorological variables from dynamically downscaled atmospheric reanalyses (NCEP–NCAR) using the WRF mesoscale numerical weather prediction model. Landfalling ARs resulted in higher precipitation amounts throughout the domain than did non-AR storms. ARs contributed the most extreme precipitation events during January and February. Daily snow water equivalent (SWE) changes during ARs indicate that high positive net snow accumulation conditions accompany ARs in December, January, and February. We also assess the historical impact of AR storm duration and precipitation frequency by considering the precipitation depth estimated during a 72-h window bounding the AR landfall date. More extreme precipitation amounts are produced by ARs in the South Cascades and Sierra Nevada ranges compared with ARs with landfall farther north. Most AR extreme precipitation events (and lower SWE accumulations) are produced during warm AR dates, especially toward the northern end of our domain. Analysis of ARs during dry and wet years reveals that ARs during wet years are more frequent and produce heavier precipitation and snow accumulation as compared with dry years. Such conditions are evident in drought events that are associated with a reduced frequency of ARs.
Dhaka is one of the fastest growing megacities of the world with a dense population over 15 million. Being the capital of a developing country like Bangladesh, it is experiencing multi-dimensional problems such as over urbanization, traffic congestion, water logging, solid waste disposal, black smoke from brick kilns and industrial emissions, sound pollution, pollution of water bodies by industrial discharge and the newly added calamity, building collapse. Dhaka is a sheer example of having poor legislative actions, inefficient management and lack of public awareness, which leads the urbanization to an unplanned and resource consuming development. This paper presents an integrated study of urbanization trends in Dhaka City, Bangladesh, by using Geographical Information Systems (GIS) and Remote Sensing (RS). This study explores the land use change pattern of Dhaka City Corporation over 1990-2010, through interactive supervised land cover classification using Landsat images by ArcGIS 10. The remotely detected land use/cover change from 1990 to 2010 shows that Dhaka is gradually changing as vegetative cover and open spaces have been transformed into building areas, low land and water bodies into reclaimed built up lands. These changes are mainly governed by unplanned urban expansion.
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