The Study On Optimal Allocation Of Coastal Shelterbelt In Eastern Zhejiang

Tropical cyclone, with its high frequency, severe disaster, huge loss, deep consequence and extensiveness, is one of the most main natural disasters in eastern Zhejiang, leading directly a severe interference to the ecological system structure of coastal windbreak and the enormous threat to the forestry production, social economy and people's life and property safety. As the important ecological barriers, Coastal shelter forest plays a key role in the aspect of soil and water conservation, wind prevention, sand-fixation and regional ecological security. However, the current coastal shelter forest system failed to give full play the comprehensive efficiency, which owing to the facts including nonuniform space distribution, unreasonable forest structure, incongruous between the macroeconomic control and micro optimization.On that basis, remote sensing image was selected as main data source, and by using of landscape ecology principles and methods, an integrated approach of RS&GIS was adopted to analyze and assess the forest landscape in eastern Zhejiang. Meanwhile, in order to make full use of coastal shelterbelt system performance, we build multi-objective, the Gradual Easy Constraint Method and employ spatial optimizing model of coastal shelterbelt on the basis of the integrated risk assessment of tropical cyclone disaster. The results show that:1, Based on the database of Aster DEM and geological data as well as GIS techniques, we make quantitative analysis of the topography of the study area through the extraction of macro-and micro-topographical factors. The results showed that: The low altitude area took up94.5%of the whole area. Mountains were high in southwest, low in northeast, SW-NE direction and wedge formation roughly. However, hypsographic feature was significant because of staggered gully and numerous mountain, basin. Surface roughness and slope correlated well with the altitude and along with the accretion of altitude, surface roughness and slope increased.2, The study of landscape indicate that The whole landscape appears a high degree of fragmentation, forest structure was unreasonable, the proportion of coniferous forests was too large, and broadleaf forests and mixed forests less than normal. The landscape change was significantly associated with the elevation rising. Generally, it presented increases in patch size, aggregation and connectivity, and decreases in fragmentation and regulation of shape on the contrary. The interference of the human activities and the impact of urbanization were the major driving forces of the degree of fragmentation.3, Between1960and2010, the impact of tropical cyclones landing eastern Zhejiang had typical characteristics in time, space and intensity. In terms of time, the number of tropical cyclones affecting eastern Zhejiang declined. The tropical cyclones from1960to1970were16.3%higher than that from2000to2010. The average landing times had the opposite trend which shows that from2000to2010, the average landing times were158.3%higher than that from1960to1970. It is a tropical concentrated periods of cyclones from July to September, especially in August. The tropical cyclones of impacting and landing accounted for32.7%and35.4%respectively. It is most possible for the tropical cyclones to land from noon to evening with the possibility of54.2%in a day. In the terms of space, it is high possible for the tropical cyclones to land with the possibility of85.4%. Cangnan and Yuhuan were the two highest risk. The path of tropical cyclone above typhoon has the most typical features with the front toward the west, northwest, and mainly concentrated in Wenling. Meanwhile in Yueqing, Cangnan, the possibility were as high as85.7%. In the terms of intensity, wind speed of landfalling tropical cyclones are concentrated between16.3m/s to27.3m/s, with the probability of up to71.7%. In the terms of regions, Wenzhou has the highest risk of tropical cyclones with high intensity, followed by Taizho and with the minimum in Ningbo.4, In the base of the spatial and intensity features of tropical cyclones, we introduce5indicators including frequency of tropical cyclone, population density, density of arable land, real GDP and the per capita output value of the tertiary industry, using analytic hierarchy process and weighted evaluation method to carry out tropical cyclone risk assessment of Eastern Zhejiang Province. The results show that: Cangnan has the highest risk of1.09which is202.8%higher than Wenzhou Ouhai with the lowest risk of0.36. In addition, the risk value at Wenling, Ninghai, Xiangshan, Yueqing and Yuhuan is also higher.5, Using the Gradual Easy Constraint Method, a muti-objective programming model was built to optimize the spatial structure of coastal shelterbelt forest. The results show that the forest area increased78273hm2with a growth of5.4%. The forest coverage rate increase from the current48.7%to51.3%with the proportion of pin, wide, mixed, change from the current6.4:2.0:0.8:0.7to4.0:3.7:1.8:0.4and forest structure is more reasonable. The total value of ecological services increased by1.535billion yuan.hm-2a-1, with a growth of3.7%. The social and economic benefits also increased by2.4%and5.5%respectively.