Mapping methane emissions from the three gorges reservoir area: A feasibility study Study area The three gorges reservoir area includes all the flooded area caused by the three gorges dam. It extends along Yangtze River, covering an area from Yichang city in Hubei Province to Chongqing area (E106o14’ – 111o28’, N25o56’ – 31o44’). (See Figure one for an overview of the three gorges dam reservoir area)  Figure one: The three gorges dam reservoir. Yangtze River is in dark blue. The reservoir area is in light blue. The area has complicated landform, with difference in altitude from 1000m to 1500m. The area has a mild climate. In extreme weather in winter, temperatures there are not less than 5 degrees below zero centigrade, while the yearly average temperature is above 15 degrees centigrade. In addition, the area's humidity can be kept at around 80 percent. Besides, the area has plentiful precipitation. The three gorges dam project consists of three stages starting in 1993 and finishing in 2009. The water level in the reservoir area will be increased step by step: Firstly, it was increased to 10-75m after the closure work on November 8th, 1997; Secondly, to 135m in June 2003; Thirdly, to 156m in 2006 and finally 175m till the accomplishment in 2009. When the normal water level of 175 m is achieved, the reservoir will cover more than 1,000 sq.km and stretch some 663km. The Three Gorges Reservoir will inundate more than 600 sq. km., the world's largest inundated area by a single project. Thus, methane emissions will be increased over this area. Proposed methodology Due to the big area (around 600-km long) and complicated topographical characteristics, remote sensing would be a very suitable tool to map the methane emissions from the three gorges reservoir area. Noticing the fact that emissions levels vary widely among reservoirs depending upon such factors as the area and type of ecosystems flooded, reservoir depth and shape, the local climate, the way in which the dam is operated and the ecological, physical and socio-economic characteristics of the dammed river basin, a spatial model is more suitable to present this variability [1]. As Ashcroft and Morel (1995) discussed, directly derive methane emissions from satellite is still not reliable. Thus, developing an indirect approach using environmental variables derived from satellite data and empirical model based on field measurements is a feasible solution, comprising the followed four steps. |