| The urban green space has become a key part of city green development and an important carrier of ecological civilization construction.It's like a "green lifeline" of the city with lots of functions like ecological protection,health and leisure,resource utilization and so on.In recent years,with the rapid urbanization process in Fuzhou,the urban green space environment is facing great stress.As the central city of the Economic Zone on the west coast of the Straits,Fuzhou has become one of China's"ten furnace cities",and the seasonal high temperature problems need to be solved urgently.In this paper,satellite remote sensing images in 1994 and 2013 were used,with the help of ERDAS 2014,ArcGIS 10.2,ENVI 5.1,to analyze the temporal and spatial evolution of green space and its cold island intensity in Fuzhou.this region can be divided into invariant area and the green space evolution area based on the different land use/cover change(LUCC)characteristics.Green space evolution area includes green space expansion,green space loss and green space exchange.According to this category,the evolution pattern of green space is analyzed in landscape aspect.A VCX-based(vegetation cooling index)quantification and vectorization method is used to analyze ecological evolution and cold island intensity change of different green space.Finally,medium and high resolution image is utilized to obtain land use/cover(LULC)of the central area of Fuzhou city based on visual interpretation.This paper analyzes cool island effect characteristics of green space,and construct a quantitative model to calculate the green space cold island intensity.Besides,the driving factors of cool island effect are explored.The results showed as follows:(l)The LULC was change obviously in 1994-2013.Invariant area of forest land,grassland,build-up land,bare land,wetland and water body were 6387.50 km2,670.81 km2,248.79 km2,19.59 km2,16.94 km2,143.04 km2,respectively.The forest land decreased by 361.13km2 with an average rate of 18.05 km2/yr,and the land use intensity was 0.23%.The grassland decreased by 153.48km2 with an average rate of 7.67 km2/yr,and the land use intensity was 0.38%.The wetland decreased by 9.69km2 with an average rate of 0.48 km2/yr,and the land use intensity was 1.67%.Change of the build-up land was most significant,increasing by 852.63 km2 with an average rate of 42.63 km2/yr,and the land use intensity was 11.59%.(2)The expansion of build-up land is divided into two categories:1)Expansion of downtown area,centering on Gulou District and Taijiang District expanding to the south of Jinan District and the southeast of Minhou District 2)Expansion of outskirt area from administrative center.61%of the new build-up land was converted from the green space,of which the forest land area was 458.58 km2,accounting for 38%of the new build-up land and the grassland area was 279.23 km2,accounting for 23%of the new build-up land.Rapid urbanization has lead to a significant stress to the urban green space.(3)The area of green space expansion,green space loss and green space exchange was 351.92 km2,846.93 km2 and 1963.59 km2,respectively.The area of green space loss is far beyond the expansion.The loss rate of green space reached 7.70%,and the expansion rate was only 3.20%.Invariant area has a highest complexity of landscape pattern,followed by the green space exchange area,the green space loss area is slightly smaller than the exchange zone,and the green space expansion area is the lowest.Invariant area and green space expansion area has lower landscape fragment index.The area advantage of forest land of the invariant area leads to lower landscape fragment index.Green space loss shows an intensive and directivity expansion mode under disturbance by human's activities.(4)1n 1994,the whole area was dominated by low temperature zone and sub low temperature zone.The green space is mainly located in the low temperature zone,and the build-up land is mainly located in the middle temperature zone.In 2013,the sub low temperature zone became the dominant temperature zone.The green space is in the sub low temperature zone.The build-up land is in the middle temperature zone and sub high temperature zone.The high temperature zone and sub high temperature zone are continuously expanding outwards based on the original region,and the expansion direction is consistent with the direction of the urban expansion.(5)Different LULC has different cold island effect.In 1994,forest land,grassland,wetland and water body has a cooling effect.The greatest contribution comes from forest land,up to 1.82?,the rest are 1.1 ?,0.57 ? and 0.42 ?;Build-up land and bare land has a warming effect,with-7.12? and-5.25? respectively.The cooling effect of the green space expansion is far below the warming effect of green space loss.In 2013,the cooling effect comes from forest land,water body and wetland in the study area,1.11? and 0.37?and 0.07? respectively.Grassland showing a warming effect,illustrates the influence of temperature effects of grassland is not fixed.With the advancement of urbanization,the warming effect of build-up land and bare land show an increasing trend,and the cold island effect of green space shows an decreasing trend.(6)Different types of green space evolution have different temperature response.The temperature change intensity is arranged,and the intensity sequencing is green space loss>green space expansion>green space exchange>invariant area.In time-space coordinates of VCX.the original point of green space loss and green space exchange is in the lower right comer,showing higher vegetation cover and lower relative land surface temperature(RLST).And the original point of green space expansion is in the upper left corner.With the evolution of green space,when the vegetation cover increase by 0.1 in the expansion and exchange area,temperature will decrease 1.81 ? and 1.63? respectively,while the point in VCX moves gradually forward to the lower right corner.When the vegetation cover decrease by 0.1 in the green space loss area,temperature will increase 5.78?,while the point in VCX moves gradually forward to the higher left corner.Green space expansion leads to cool island effect to a certain extent,but the temperature reduction caused by green space expansion cannot offset the temperature rise caused by green space loss.(7)The green space in the urban central area has a significant cool island effect,which decreases with the increase of the geometric distance from the green space.The maximum cooling value and the maximum cooling distance are 10.81? and 450.77m respectively.The greater actual area of green space,the more significant of its cooling effect is. |
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