Effect of Urban Heat Island on Growth Rate of the Convective Boundary Layer Over Baghdad City

Abstract

Due to human activities and economic growth, in the last decades, urban expansion has increased, and it has a large role in the formation of urban heat island. Urban heat island effects natural physical properties of the air. In this study, data from satellite images included Landsat5 Landsat 9 and reanalysis data from European Centre for Medium-Range Weather Forecasts (ECMWF) by ERA5 model are implemented. ERA5 archives NetCDF file data for many hourly atmospheric elements such as temperature, wind components, sensible heat flux, boundary layer height …etc. All the files were processed by MATLAB, while satellite images processed by ArcGIS to calculate the spectral index such as Normalized difference built up index (NDBI) and supervised classification. Results of composited images and supervised classification show that there is an increase in built up area of about 23% for the periods from July-1994 to July-2022. This change in LULC will create urban heat island for Baghdad and affect heat budget near the surface that will change structure of urban boundary layer, and convective boundary layer (CBL). Near the surface there is an increase in growth rate of convective boundary layer about 0.25m/s at 7AM for July-2022, relative to 0.136 m/s for July-1994. This difference in growth rate is due to urban heat island creation and will increase CBL to about 620m in 2022 relative to 1994 at 10AM.