Urbanization in China has expanded at an unprecedented speed since the declaration of "Reform and Open Policy"and presented many challenges. Unbalanced regional development, appearance of super megacities an...Urbanization in China has expanded at an unprecedented speed since the declaration of "Reform and Open Policy"and presented many challenges. Unbalanced regional development, appearance of super megacities and concomitant problems,and conflicts between urbanization and cultivated land protection are three critical problems that Chinese urbanization has to face. To develop new plans for foreseeable future urbanization in China, it is critical to understand the evolving history of cities across China. This study maps urban expansion of 60 typical Chinese cities based on large amount of remote sensing data and the labor-intensive image interpretation method, in order to understand the history of urban expansion from the 1970 s to 2013.Results showed that area of cities expanded 5.23 times compared to their area in the 1970 s. Urban expansion in China accelerated three times(1988–1996, 1999–2006, and 2009–2011) and decelerated three times(1997–1998, 2007–2008, and 2012–2013) over the 40 years. The urban area of South China expanded most significantly 9.42 times, while the urban area in Northeast China expanded only 2.37 times. The disparity among different administrative ranks of cities was even greater than(3.81 times) the differences among different regions. Super megacities have been continuously expanding at a fast rate(8.60-fold), and have not shown obvious signs of slowing down. The proportion of cultivated land among the land sources for urban expansion decreased to a small extent in the 1990 s, but cultivated land continues to be the major land source for urban expansion. Effective future urbanization needs controlling the expansion scale of large cities and reasonably developing medium and small cities, as well as balancing regional development.展开更多
Characteristics of the drought periods which occurred in North Africa,Middle East,Middle Asia and Northwest China were studied based on the analysis of rainfall data from 1870—1990.It is found that the drought period...Characteristics of the drought periods which occurred in North Africa,Middle East,Middle Asia and Northwest China were studied based on the analysis of rainfall data from 1870—1990.It is found that the drought periods first started in North Africa and expanded eastward to Northwest China through Middle East and Middle Asia in about 27.5 years.And then a new teleconnection pattern of 30—50 day low-frequency oscillation which is associated with the droughts over the Africa-Asia Con- tinent was discovered.Finally,a hypothesis is proposed based on the statistical results that the east- ward expansion of drought periods may be caused by the occurrence of giant earthquakes(Ms>6.0) which have a tendency to shift eastward from North Africa to Northwest China in about 27.75 years.展开更多
基金supported by National Natural Science Foundation of China(Grant No.41201443)“One-Three-Five”Strategic Planning Program by the Institute of Remote Sensing and Digital Earth(Grant No.Y4SG0100CX)National Remote Sensing Centre of China
文摘Urbanization in China has expanded at an unprecedented speed since the declaration of "Reform and Open Policy"and presented many challenges. Unbalanced regional development, appearance of super megacities and concomitant problems,and conflicts between urbanization and cultivated land protection are three critical problems that Chinese urbanization has to face. To develop new plans for foreseeable future urbanization in China, it is critical to understand the evolving history of cities across China. This study maps urban expansion of 60 typical Chinese cities based on large amount of remote sensing data and the labor-intensive image interpretation method, in order to understand the history of urban expansion from the 1970 s to 2013.Results showed that area of cities expanded 5.23 times compared to their area in the 1970 s. Urban expansion in China accelerated three times(1988–1996, 1999–2006, and 2009–2011) and decelerated three times(1997–1998, 2007–2008, and 2012–2013) over the 40 years. The urban area of South China expanded most significantly 9.42 times, while the urban area in Northeast China expanded only 2.37 times. The disparity among different administrative ranks of cities was even greater than(3.81 times) the differences among different regions. Super megacities have been continuously expanding at a fast rate(8.60-fold), and have not shown obvious signs of slowing down. The proportion of cultivated land among the land sources for urban expansion decreased to a small extent in the 1990 s, but cultivated land continues to be the major land source for urban expansion. Effective future urbanization needs controlling the expansion scale of large cities and reasonably developing medium and small cities, as well as balancing regional development.
文摘Characteristics of the drought periods which occurred in North Africa,Middle East,Middle Asia and Northwest China were studied based on the analysis of rainfall data from 1870—1990.It is found that the drought periods first started in North Africa and expanded eastward to Northwest China through Middle East and Middle Asia in about 27.5 years.And then a new teleconnection pattern of 30—50 day low-frequency oscillation which is associated with the droughts over the Africa-Asia Con- tinent was discovered.Finally,a hypothesis is proposed based on the statistical results that the east- ward expansion of drought periods may be caused by the occurrence of giant earthquakes(Ms>6.0) which have a tendency to shift eastward from North Africa to Northwest China in about 27.75 years.
