Urban Heat Island and Urban Dry Island in Moscow and Their Centennial Changes

The long-term dynamics of both urban heat island (UHI) and urban dry island (UDI) intensities over the city of Moscow, Russia, has been analyzed for the period from the end of the nineteenth century until recent years using data of the ground meteorological network. Besides traditional maximum heat/dry island intensity, an additional parameter-station-averaged intensity as a mean difference between the data of all urban and rural stations-has been used. The traditional maximum (mean annual) UHI intensity in Moscow was nearly 1.0 degrees C at the end of the nineteenth century, 1.2 degrees C one century ago, 1.5 degrees-1.6 degrees C both in the middle and at the end of the twentieth century, and 2.0 degrees C in recent years. The station-averaged UHI intensity was equal to 0.7 degrees-0.8 degrees C in the second half of the twentieth century and increased up to 1.0 degrees C in recent years. It is probable that stabilization of both parameters from the 1950s to the 1990s was connected with the extensive city growth at that time (mass resettlement of inhabitants from the overpopulated city center to the new urban periphery since the 1960s). The new increase of UHI intensities is the result of the new intensive city growth. The relative humidity in Moscow significantly decreased during the last 146 years (mostly because of warming), unlike water vapor pressure. The UDI is closely connected with the UHI; the absolute value (modulus) of its intensity is increasing in time from -4% at the end of the nineteenth century to -9% now. During the last two decades, the UDI as well as the UHI became much stronger than before.