This study was conducted to identify the distribution characteristics of the impervious area in urban watersheds and to reduce the deviation of the impervious area ratio that occurs depending on the degree of construction of land surface condition data. The average impervious area ratio by land use that can be applied to the calculation of the urban impervious area ratio was derived by statistically analyzing the distribution characteristics of the impervious area ratio by land use according to the urban watershed conditions. In urban watersheds, the change in impervious area ratio over the past 20 years has continuously increased in watersheds with an impervious area ratio of less than 60%, and decreased in watersheds with a high impervious area ratio of 60% or more. The average impervious area ratio by land use applicable to the land use technique is “Residential area” 84.0%, “Residential and commercial mix” 93.6%, “Commercial and business facilities” 89.8%, “Industrial land” 84.8%, “Public land” 47.3%, “Transportation facility” 93.3%, “Urban revitalization facility” 61.1%, “Bare land” 17.6%, “Special area” 11.4%, “Forest and open space” 3.5%, “Rivers and lakes” 9.2%. As a result of examining the adequacy of the average impervious area ratio by land use, the difference between the calculated value of the impervious area ratio using land use techniques and the actual impervious area ratio of the biotope map ranged from -3.0%p to 2.6%p at the significance level of 95%. In addition, when the watershed condition is applied, the difference ranged from -2.3%p to 1.7%p. By applying the average impervious area ratio by land use derived in this study, it was found that the impervious area ratio of the target urban watershed could be calculated within a deviation of ±3%p.

Heatwaves are one of the most common phenomena originating from changes in the urban thermal environment. They are caused mainly by the evapotranspiration decrease of surface impermeable areas from increases in temperature and reflected heat, leading to a dry urban environment that can deteriorate aspects of everyday life. This study aimed to calculate daily maximum ground surface temperature affecting heatwaves, to quantify the effects of urban thermal environment control through water cycle restoration while validating its feasibility. The maximum surface temperature regression equation according to the impermeable area ratios of urban land cover types was derived. The estimated values from daily maximum ground surface temperature regression equation were compared with actual measured values to validate the calculation method’s feasibility. The land cover classification and derivation of specific parameters were conducted by classifying land cover into buildings, roads, rivers, and lands. Detailed parameters were classified by the river area ratio, land impermeable area ratio, and green area ratio of each land-cover type, with the exception of the rivers, to derive the maximum surface temperature regression equation of each land cover type. The regression equation feasibility assessment showed that the estimated maximum surface temperature values were within the level of significance. The maximum surface temperature decreased by 0.0450˚C when the green area ratio increased by 1% and increased by 0.0321˚C when the impermeable area ratio increased by 1%. It was determined that the surface reduction effect through increases in the green area ratio was 29% higher than the increasing effect of surface temperature due to the impermeable land ratio.