Modern Changes of the Urban Heat Island in Moscow

According to the meteorological network data for the period of 1991-2020, as well as the radiometric measurements of the surface temperature T-S of Moscow region by the Terra and Aqua satellites over the period of 2000-2020, the daily course and long-term changes in the urban heat island (UHI) of Moscow in the field of both air temperature T at a height of 2 m and T-S are studied. For the analysis of T-S, 1379 satellite images over 21 years in clear and slightly cloudy sky, when UHI analysis is possible, are selected. The average annual values of T-S were obtained using their normalization by separate seasons. The daily course of Moscow UHI in the air is weakly expressed, especially when compared with the rural area not only of the city center, but also of its entire area: only the weakening of this phenomenon in fall and in the prewinter season (from October to December) is reliable. According to the satellite data, the surface UHI is marked by a maximum in June-July with the strongest vegetation development and a minimum in fall when leaves fall, with intermediate values in winter and spring. The rapid growth of T took place in 1991-2020 both in Moscow and in rural areas at approximately the same speed. As a result, there have been no statistically significant directional changes in the UHI intensity both in the air and on the surface as a whole over the past 20-30 years. The likely reasons for the general stabilization of the UHI in Moscow are both natural and socio-economic factors: the approximate constancy of the probability of clear weather (which contributes to intensification of this phenomenon) and the biomass in the region (which determines heat losses due to transpiration), deceleration and cessation of the growth of the population and energy consumption of the city, and deindustrialization. Additional reasons are the gradual relocation of residents to the new outskirts of Moscow, as well as quarantine restrictions due to the COVID-19 pandemic in 2020.