Surface urban heat island of Iasi city (Romania) and its differences from in situ screen-level air temperature measurements

Nowadays, in the field of urban climate there is a scientific need to compare Land Surface Temperature (LST) with screen-level air temperature (2mTair). This is done in our study for Iasi city, based on MODIS imagery and in situ observations. We assess firstly the Surface Urban Heat Island (SUHI) under clear-sky conditions, outlining that SUHI is well expressed during the year, while its geometry tends to be more compact and regular during nighttime. In summer daytime SUHI extension reaches its peak, being outlined by the 35 degrees C isotherm, while in winter SUHI is absent during the day. LST increases clearly when imperviousness ratio (IMD) overpasses the 10% threshold, and its maximum is reached for IMD higher than 80%. The comparison with the in situ observations indicates that the LST - 2mTair differences are the highest during daytime in spring and summer (+ 5 to +7 degrees C), while during winter no major differences are observed. For the nighttime the LST is generally 1 to 3 degrees C lower than 2mTair. We also found that intense radiative conditions are prone to increase both the SUHI intensity, and the difference between LST and 2mTair. The results are meant to support the policies aiming to mitigate the heat island effects on human population.