Thermal Environmental Effects And Driving Factors Of Major Human Land Use Activities In Subtropical Humid Regions

Through land use activities,human beings are changing the Earth system at an unprecedented speed.Over half of the global biomes have been changed by human activity.By changing the geophysical and geochemical processes of land creatures,the two primary types of human land use activities,namely,agriculture and urbanization,can greatly alter local,regional and global climate,especially the temperature.On a regional scale,urbanization and agricultural activities often co-occur,while in most cases,the rapid expansion of urban land is realized through the encroachment of agricultural land.A comprehensive evaluation of how they affect regional temperature is a prerequisite for accurately gauging the climatic effects of human land use activities.Nonetheless,previous research that focuses heavily on the impacts of deforestation or urban heat island effects does not fully reveal the overall effects of human land use activities on regional temperature.Taking Jiangxi province as an example and natural forests as the reference,this paper drew on the data of MODIS land surface temperature from 2003 to 2019 to comparatively study the effects of agricultural and urban land use on surface temperature as well as the driving factors,and then explored the effects of agriculture and city land use change on regional atmospheric temperature with the observation-minus-reanalysis(OMR)method,based on the observational data obtained by 81 weather stations and NCEP/NCAR-1 reanalysis data.Results are listed below:(1)Compared to natural forests,agricultural land warms the land surface during the day,with an annual mean temperature increase of 1.97?,and cools the surface substantially at night,with an annual mean temperature decline of-0.3?;the thermal environment effects of agricultural land vary greatly by season,especially at night,characterized by weak nighttime warming effects during summer;both the daytime warming and nighttime cooling effects of agricultural land show upward trends from 2013 to 2019,the rates of change being 0.105?,/10a and-0.084?/10a respectively.(2)Urban land has warming effects both during the day and at night,with an annual mean increase of 4.36? and 0.54? respectively,considerably higher than agricultural land does;the thermal environment effects of urban land vary greatly by season,characterized by the significantly stronger warming effects in summer and the slight cooling effects observed even at winter night;from 2013 to 2019,the daytime warming effects of urban land show upward trends,the rate of change being 0.399?/10a,whereas no discernible trend of change has been observed at night.(3)The spatial distribution of the thermal environment effects of both agricultural and urban land has a significantly negative correlation with evapotranspiration(daytime and nighttime)and surface albedo(nighttime),yet a weak correlation with climatic factors;The intra-annual change of both types of land(except for the daytime thermal environment effects of agricultural land)has an overall negative correlation with evapotranspiration and surface albedo,and a positive correlation with climatic factors(precipitation and temperature);the annual change of both has complex relationships with various driving factors,which does not show any consistent correlation.(4)According to results based on observed meteorological data,from 2003 to 2019 the mean atmospheric temperature in the studied region shows significant upward trends,the rate of change being 0.33?/10a,and the rate of increase in the minimum temperature(0.53?/10a)is considerably higher than that in the maximum temperature(0.12?/10a);OMR-based results suggest that the change in land use contributes 18%to the increase of regional mean temperature respectively.The findings of this research highlight the dramatic effects of urban and agricultural land on regional temperature change,especially the warming effects of agricultural land,which takes up a larger area.Nonetheless,owing to the differences of remote sensing and meteorological observation in the height and rationale of temperature monitoring,as well as the dissimilar methods for evaluation,there are discrepancies between the results obtained from the two approaches on how the change in agriculture and city land use affects regional temperature.Specifically,according to the results from remote sensing in daytime,the increase in surface temperature is overall higher than that in atmospheric temperature,while the trends at night are the other way round.The research in this paper has both theoretical and practical significance to the formulation of land use strategies for mitigating regional climate change.In the future,multiple methods should be combined to comparatively study the climatic effects of human land use activities and the underlying mechanism.