Urban Heat Island Mechanism And Forecast In Fuzhou

As a typical representative city with the climate of“hot summer-warm winter”insubtropical area,Fuzhou was named as“the first furnace city”in China based on the annual32.6 days with high temperature(above 35°C)in recent 30 years.The hot-summer has been the primary obstacle for Fuzhou as a favorable living city,the UHⅡ problem should reasonably be the serious topic for Fuzhou.The paper aimed to search for the dynamic and mechanism of UHⅡ in Fuzhou in recent 20 years by use of the multi-discipline knowledge in the field of landscape ecology,geo-statistics,and urban planning etc.,coupled with the Remote Sensing(RS)and Geographical Information System(GIS)technologies to process four summer LANDSAT images from 1996 to 2016,urban POI(point of interest),and urban road maps.The results showed the annual variation,thermal landscape pattern and urban profile variation characteristics of the UHⅡ in Fuzhou.The UHⅡ mechanism quantitative model was built with four spatial scales:0.5 km×0.5 km,1 km×1 km,2 km×2 km and 3km×3 km,which displayed the co-relationship between the UHⅡ and 23 impact factors.Then the paper simulated the dynamics of UHⅡ in 2020 and 2030 based on CA-Markov model with three scenarios.Finally,the mitigating measures of UHI was proposed in Fuzhou.The detailed results was listed in this paper.(1)UHⅡ Dynamic in Fuzhou:The UHⅡ and its extent was deteriorated gradually during the recent 20 years,which was consistent with the urban expansion.The areas of the UHⅡ low grades and high grade changed from 102.03 km~2 and 216.41 km~2 to 98.34 km~2 and220.10 km~2,respectively.The UHⅡ gradient from the suburban to city center was obviously strengthened.The cold island was distributed in a ring shape,while the heat island was distributed to the whole area with“multi-hot-center”.The UHⅡ patches decreased 2,607 and transformed into the large“strong heat island”patch.The UHⅡ profile showed that the normalized temperature change in west-east profile from 0.76°C,0.83°C,0.90°C to0.73°C,while that in the north-south profile from 0.81°C,0.82°C,0.83°C to 0.91°C.(2)UHⅡ Mechanism in Fuzhou:The integrated model was built with the fitting R~20.831 between the UHⅡ and its impact factors listed as urban land cover,urban land-cover pattern and urban anthropogenic activity intensity.The influential order was listed as:urban land cover>urban anthropogenic activity intensity>urban land-cover pattern.The urban land cover has overall 74.47%-84.14%interpretation to UHⅡ on 3 km scale,among which the independent interpretation to UHⅡ for the impervious surface 28.59%-76.76%,the joint interpretation to UHⅡ for the green space and water body 27.94%-58.25%.The impervious surface is positively correlated with UHⅡ with the fitting R~2 0.768,which means that the normalized UHⅡ is proposed to increasing 0.476°C provided that the impervious surface increases 1 unit.The green space and UHⅡ are negatively correlated with the fitting R~20.357 with the UHⅡ reducing 0.36°C at the 1 unit increasing of the urban green space.The water body and UHⅡ is negatively correlated with the fitting R~2 0.477 with the UHⅡ reducing 0.785°C at the 1 unit increasing of the water body.For the urban landscape structure,the overall interpretation rate of UHⅡ reached 62.74%-82.67%on the 3 km scale.For the intensity of urban anthropogenic activity,the overall interpretation rate of UHⅡ reached 18.01%-40.93%.The UHⅡ is supposed to increases 0.285°C and 0.123°C respectively at the increasing of one additional unit of road density and POI density.(3)Prediction for the UHⅡ in Fuzhou:By use of CA-Markov model,the paper built the UHⅡ dynamic model with the 88.73%precision based on the UHⅡ from 1996 to 2016.Comparing the status of Fuzhou UHⅡ in 2020 and 2030 with 2016,Under the natural growth scenario,the area of the cold island increase 8.46 km~2 and 6.36 km~2 respectively while the weakest heat islands decreasing 8.79 km~2 and 9.30 km~2.Under the ecological protection scenario,the area of the cold island increase 6.74 km~2 and 7.44 km~2 respectively while the strongest heat island reducing 1.62 km~2 and 2.05 km~2.Under the deterioration scenario,the area of the strongest heat island increase 8.00 km~2 and 7.84 km~2 respectively.(4)The mitigating measures for UHⅡ in Fuzhou:The paper clearly pointed out the 40heat island centers.In order to mitigate the UHⅡ in these centers,the paper designed the different technical measures listed as:to paint the walls with the light-colored paintings for buildings,to build vertical greening,roof greening,under-floor ventilation area and shading area,to adjust road greening modes with the strong water permeability pavement materials,to restore urban water bodies with the control of the construction intensity on both sides,to improve the greenness of the revetment.