| The Heihe River Basin is one of the most vulnerable ecological environment areas in China. Recently, in researches and practice such as land planning and regional sustainable development, the Heihe River Basin is one of the most active areas, and its water contradiction has day outstanding, which puts forward the ordeal of the development of oasis in the middle and lower reaches of Heihe River, especially increased oasis in the middle area of artificial oases which decline the function of ecological barrier and even make it become one of the important sandstorm source. Studying changes in increased oasis in the middle area of artificial oases provides basic basis and the reference for protecting the ecological environment and the local ecological environment management and preventing sand.The paper used the literature material and long time series data of remote sensing images, in view of the different data sources, adopted the literature material reconstruction, object-oriented image segmentation and automatic threshold extraction combining with visual interpreting method to extract the heihe river basin oasis data from1949to2009. Used ArcGIS map algebra operation method to compose the extraction oases data and desert data of1963,1968,1973,1977,1980,1986,1990,1993,1996,1999,2002,2006,2009into composite data of time and space, used the space analysis tools to determined the conversion of the spatial pattern of the oasis, based o it, analyses the oasis expansion or atrophy status and the basic model of the oasis’change of different period of thirteen different periods, identified and determined hotspots of oasis change according to the13periods of oasis and desert synthesis data, explored the evolution of the desert oasis pattern characteristics and laws in the Heihe River Basin. The result shows that:Firstly, in view of time and space distribution pattern, the oasis of the Heihe River Basin mainly distributed in Heihe River and its tributaries, Peking University on both sides, and along the river flows and cross-strait outward expansion. Early oasis plaque is broken. They are mainly distributed in the central part of the ShandanCounty, folk music county central and north central ganzhou borough and in the northwest and southern stronghold county, Linze County central, Ejina things on both sides of the river since2000and oasis radical expansion, these areas of oasis even piece, the oasis of unit distribution pattern of the characteristics of the heihe river basin is complex topography and landforms and regional water resources of the decision. Secondly, in view of area change, the oasis area have experienced process of radical changes, stable progress and rapid expansion, in Heihe River, which reaches the maximum value of6766.49km2; the change of area are obviously different in each oasis unit, the change of oasis area have similar tendency between Shandan County and Minle County, the area of the oasis unit of Zhangye, Linze and Gaotai is in one comparatively steady state basically. The area have the dynamitic change in each unit in the lower reaches of Heihe River, the area has relatively smooth change, but the reiterative change in the piedmont zones; on area change of each County view, the change of oasis area have similar tendency between Shandan County and Minle County, and also the change of oasis area are basically consistent among Ganzhou, Linze, Gaotai. It is that the area have dynamitic change both of Jinta and Ejina, besides, the oasis area remain at comparatively high levels both of Ganzhou and Suzhou.Thirdly, quantitatively, the expansion of oasis reaches a maximum value in Heihe River in1973, the annual area of expansion is biggest in1980, which is393.11km". The atrophy of oasis reaches a maximum value in1977, and the area is1084.54km2, the annual area of atrophy is biggest in1977, which is271.14km2; the great expansion most are distributed in1973and1980in each unit, on the contrary, the great atrophy most are distributed in1977and1999. The maximum value of annual area of expansion most occur in1980, but the minimum value most in1990. The maximum value of annual area of atrophy most occur in1977and1999, but the minimum vale most in2006; the great expansion most are distributed in1968and1973, on the contrary, the great atrophy most are distributed in1968and1980in each County. The maximum value of annual area of expansion most occur in1980, but the minimum value most in1990and2002. The maximum values of annual area of atrophy most occur in1980, but the minimum vale most in90th.Fourth, from the process point of view, the development of oasis has been gradually transited from the state of unstable to the state of stable in Heihe River basin. The change is the most violent in Ejina Delta unit, the change is specially stable in the Gan Lin Gao unit; in view of county-level, the change is the most violent in Jinta County, the change is especially stable in Ganzhou in each County. The spatial change which of oasis unit is in front of the mountain, mostly occur in piedmont zones, and the oasis characterized by alternating expansion region and atrophy region. The changes of oasis unit mostly occur on the southern bank of the branch in the middle of Heihe River, and also mostly are located in Yanjian beach. The change of oasis unit mostly occur on the northern of this unit and the banks of river in the Beida River, these areas have a lot of water and wetland, the spatial change of oasis unit become more complicated in the lower reaches of Heihe River.Fifth, in view of change model, it have seven change models for oasis in Heihe River, the area for the pattern of stable without change always is the biggest; the ratio of area for the pattern of steady atrophy come down every year; the ratio of area for the pattern of steady expansion is quite high, and increasing each year, especially, it more expands from2000; the ratio of area for the pattern of intermittent change is great lower, and a downward trend;the ratio of area for the pattern of recent change is bigger, and a downward trend, but this model widely distributed; the ratio of area for the pattern of early change is a downward trend.Sixth, in view of hot region, the hot regions for oasis distribute in each county in Heihe River, and the major portion of hot regions locate in periphery of the oasis, the change of area have great different in hot regions. The area of hot region of Ejina oasis is the biggest in lower reaches of Heihe River, which reached148.91km2; the type of transition has varied from place to place in hot region in each County. |
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