Study On The Influence Of Land Use Spatio-temporal Pattern On Urban Thermal Environment

Urbanization has changed city underlying surface constantly,which is performed by transition among land use types.Different types own varying physical characteristics that decide the influence on thermal environment.Studying influencing mechanism of land use on thermal environment scientifically is important for mitigating the deterioration of thermal environment and raising the measures for improving the thermal environment.This paper analyses land use change and surface thermal change in Jing-Jin-Ji Region using 2005 and 2015 land use data and MODIS surface temperature products and identifies contributing roles of land use types.The influence of construction land spatial structure on the urban thermal environment is discussed,and the measures are put forward from land use allocation plan and construction land optimization spatially.Results are as follows:(1)The area of Jing-Jin-Ji Region is mainly farmland,and the area of water and unused land is small.Forest land and grass land are distributed over north-east mostly.Farmland,rural settlement and urban construction land are distributed at North China Plain.Land use type change was obvious from 2005 to 2015,shown as farmland decreasing and urban construction land increasing.The farmland was reduced by 6842km~2,and the urban construction land was increased by 6652km~2,which accounted for 3.20%and 3.11%of the study area respectively.Different cities had different land use features,in Qinhuangdao farmland only reduced 84km~2,in Shijiazhuang and Baoding farmland reduced more than 900km~2.In Beijing and Tianjin construction land made about 55%increasing.Growth of construction land in Hebei province were more than 100%.Considering spatial pattern,the new urban construction land was mostly distributed around the original urban construction land or along the roads,and the patches of urban construction land were enlarged.(2)The average annual land surface temperature in Jing-Jin-Ji Region was increasing.Daytime average land surface temperature increased by 0.97?in 2015 compared with that in2005.The linear variation rate was 0.367?/10a.In spring,summer and winter surface temperature rose,linear change rates were over 0.5?/10a.Daytime temperatures decreased in autumn,the linear change rate was-1.53?/10a,the downward trend was obvious.Annual surface temperature rising area was mainly located in the North China Plain,among which Langfang was the most prominent.Thermal patterns of defferent seasons showed large differences.In spring and autumn,middle-heat grade was main type,the thermal pattern was fragmentized.In summer thermal environment mostly was in higher grade.In winter surface thermal grade showed rising with latitude level gradually going up from south to north.(3)Different land types played different role to thermal environment under varying situation that differs between seasons and day and night.Forest land and grassland were cooling types,urban construction land and rural settlement were heating types.Farmland does heating during daytime and summery night and cooling during other seasons'night.Forest land and grassland cooling strength was raising between 2005 to 2015,showing as the increased CI.The CI of urban construction land and rural settlement went up,so the heating strength was stronger.Farmland'CI had decreased,so that its heating ability was getting weak.Different land use types played different climatic roles and own different functional strength under varying situations.(4)Urban construction land structure of cities in Jing-Jin-Ji region had almost experienced little change,most of the new construction patches were attached to the original construction land and expand on the basis of the original.In 2015 construction land UHII was lower than in2005,but original construction land UHII in 2015 was higher than 2005.(5)Types of new urban construction land expansion are divided into infilling,edge-expanding and enclave-expanding.Influenced by construct and policy,edge-expanding was main type in the recent 10 years,and infilling type land only accounted for 1.09%of new urban construction land.Different cities had different expanding style.Making comparison among 3expanding types'UHII,infilling>edge-expanding>enclave-expanding.Covering thermal upgrading distribution to land use change spatially,edge-expanding patches were highly similar with new heat island patches,they had high spatial coincidence.