Spatiotemporal Changes of Urban Land Surface Albedo Impact on Thermal Environment in Bucharest Metropolitan City

This study aims to identify the impact of increasing urbanization in the Bucharest metropolitan area in Romania on the regional climate by analyzing spatiotemporal changes in MODIS Terra/Aqua geospatial and in-situ time series of land surface albedo and climate parameters during the 2002- 2022 period. Additionally, this paper quantifies the effect of urban spatiotemporal land surface albedo changes in urban thermal environment. Our analysis combined multiple long-term satellite products (e.g., land surface temperature-LST, normalized vegetation index/Enhanced Vegetation Index –NDVI/EVI, land surface albedo -LSA, leaf area index-LAI, evapotranspiration-ET) with high-resolution land cover datasets in a complex statistical and spatial regression analysis. During summer hot periods, the findings of this study reveal a strong inverse correlation between LSA and LST (r= -0.80; p<0.01) in all city sectors associated with a high negative impact on the urban thermal environment. As a measure of urban surface thermal properties, broadband albedo depends also on the atmospheric conditions. As a key parameter in urban climate research, LST interannual variations in relationship with air temperature –AT is very important in urban climate studies. The rank correlation analyses revealed that, at the pixel-scale, during the summer season (June-August) air temperature at 2m height AT and LST presents a strong positive correlation (r= 0.87%, p<0.01). During summer periods (June – August), LST-NDVI shows an inverse correlation (for central city areal r= -0.24, p< 0.05; and for metropolis areal r= -0.69, p<0.01). However, urban/periurban vegetation land covers may have major feedback to the anticipated urban climate change modeling scenarios through albedo changes due to the fact that the urban physical climate system is extremely sensitive to land surface albedo.