Sensitivity study of urban energy balance to albedo, emissivity and heat capacity in Seoul Metropolitan Area

As urban populations increase, urban heat island effect is enhanced and urban heat stress and air pollutant concentrations increase. Sensitivity experiments of changing the albedo, emissivity, and heat capacity of urban facets can provide information to mitigate the heat island effect and allow the model to study urban climate more accurately. Experiments on sensitivity of the surface energy balance of albedo, emissivity and heat capacity in the metropolitan area of ​​Seoul were conducted using Met-Office-Reading Urban Surface Exchange Scheme (MORUSES) of Unified Model Local Data Assimilation and Prediction (UM LDAPS) model. The analysis period is a heat wave period from July 15 to 21, 2018, which is a clear day without cloud and precipitation. Comparing 1.5-m temperature of AWS data, it overestimated about 0.5-2K in the model. If the albedo decreases, the net radiation, storage heat, sensible heat and ground heat fluxes increase after sunrise. Storage heat becomes negative in the afternoon, and sensible heat is positive during the night. When the albedo decreases, the air temperature increases. As the emission rate decreases, the air temperature increases as storage heat decreases and sensible, latent and geothermal heat increases, which is more intense at night than during the day. When heat capacity decreases, sensible and ground heat increase during the day, storage heat decreases, and vice versa at night. Air temperature increases during midday when solar radiation is strong and decreases elsewhere. Considering that the LDAPS-MORUSES model underestimates the air temperature, albedo and emission rates can be reduced to achieve more accuracy.

Acknowledgement: This research was supported by the Korea Meteorological Administration’s National Institute of Meteorological Sciences "Development of Biomechanical Meteorological Technology" (1365003004).