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| Changes in the Yellow River Delta, 1989-2000 |
| Overview |
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Underlying Science Coastal change caused by the effects of global warming and sea level rise, increasing population and development along all the world’s coastlines, and human modifications of coasts (subsidence, seawalls, jetties) is a global issue. The Chinese coastline along the Gulf of Bohai has always experienced dramatic changes — the delta of the Yellow River is the fastest changing coast on the Earth’s surface. Because the river carries an extremely heavy sediment load, the lower river channel silts up rapidly, resulting in frequent river course changes. The river has been engineered for millennia, but recent water demands and water diversions (amplified by several years of drought in the 1990s) have resulted in little or no water reaching the coast. Dramatic changes in the tip of the Yellow River delta were documented by astronauts on the Space Shuttle between 1989 and 2000. Over this time, several hundred square kilometers have accreted and eroded from the coast. The delta grew nearly 400 km2 between 1989 and 1995, then began eroding back. In 1997 a new channel was cut near the tip of the delta, providing the water and sediment a shorter route to the sea. Between 1995 and 1997, the delta area eroded back about 255 square kilometers. From 1997 to February 2000, the delta tip again grew nearly 100 square kilometers. Application Remote sensing and image analysis of image data are efficient strategies for examining regional changes that occur over large areas, and are a way of providing context for smaller-scale changes. The photographs collected by astronauts can be assembled in a time series of images demonstrating both the scale and specific locations of coastal change. Quantitative measurements can be made when the images are referenced to standard maps. Such analyses can identify both natural and human-induced changes, lending some understanding of the processes involved in the coastline evolution. The Crew Earth Observations payload on the International Space Station will target rapidly changing wetlands in southeast Asia, such as the Yellow River. |
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