Urban green space and albedo impacts on surface temperature in Bucharest metropolitan area

Rapid urbanization exacerbates spatiotemporal changes of urban surface albedo, an essential biophysical variable in surface energy balance and the health risks of climate warming. Through statistical and spatial regression analysis of the time series MODIS Terra/Aqua and in-situ monitoring data of climate variables for both central city and metropolitan area, this study identified the impact of urban built in Bucharest metropolitan area on spatiotemporal variation of land surface albedo (LSA) during 2002- 2023 period, and quantified its relationship with urban thermal environment (land surface temperature-LST and air temperature at 2m height AT) and associated vegetation (normalized vegetation index– NDVI, leaf area index-LAI, evapotranspiration-ET) and other climate factors. During summer hot periods, this study found a strong inverse correlation between LSA and LST (r= -0.85; p<0.01) in all city sectors explaining high negative impact on the urban thermal environment. Also, as a measure of urban surface thermal properties, land surface albedo depends on the atmospheric conditions. At the pixel-scale, during the summer season (June-August) air temperature at 2m height AT is positively correlated with LST (r= 0.86%, p<0.01). For summer periods (June – August), LST shows an inverse correlation with NDVI for both central Bucharest city (r= -0.29, p< 0.01) and for metropolitan area (r= -0.67, p<0.01). Because urban climate system is highly sensitive to land surface albedo changes, urban/periurban vegetation land covers may have strong feedback to the anticipated climate warming. Future climate adaptation strategies must consider albedo cooling benefits and urban greening that can reduce the heat exposure of urban populations.