A researcher from Lomonosov Moscow State University's Faculty of Geography Mikhail Lokoshchenko has discovered the complex nature of changes in temperature and relative humidity in Moscow over the period of many years, from the end of the 19th century to the present day. The results were published in Journal of Applied Meteorology and Climatology.
The author has studied centennial changes in "urban heat island" (UHI) and "urban dry island" (UDI) in Moscow. "Urban heat islands" are zones of higher temperatures above cities and industrial districts, appearing due to human-induced heat emissions, lower heat losses on evaporating and transpiration by plants, of which there are few in the cities, and due to other causes. This phenomenon is well-known in urban climatology, but the long-term changes in "urban heat islands" intensity and their causes remained practically unknown until now. Intensity of UHI means the difference between the air temperature in the city and outside of it. "Urban dry islands" are the zones of regular decrease in relative air humidity in big cities, which were only studied using short-term data before.
"For the first time in this work, a centennial analysis of both phenomena has been carried out, starting from 1887 (for the relative humidity field - from 1891), maps of average air temperatures and relative humidity in Moscow in different time periods have been created, trends of these phenomena changing over time have been studied. Besides traditional maximum heat/dry island intensity an additional parameter - "station-averaged" (i.e., averaged by the whole city area) intensity of heat and dry islands - has been used to analyze them", - Mikhail Lokoshchenko, Ph.D., leading scientific researcher of Department of Meteorology and Climatology of Lomonosov Moscow State University Faculty of Geography, told us.
To explain the changes over the period of many years the researcher used the data on population density (in the city as a whole as well for its central part), and the data on energy consumption in the city. During the analysis the author has discovered that the UHI intensity stabilized during the second half of the 20th century, probably because of the extensive growth of the city at that time. In the last 20 years, however, both UHI and UDI intensities have increased due to urban densification, including infill in the city center, to the increase in population density and energy consumption. The station-averaged UHI intensity in Moscow equals now 1 ºC, i.e., the capital in general is warmer than the surrounding region by 1 ºC. The maximum intensity - higher temperature in the city center compared to rural areas around it - has come up to 2 ºC.
Mikhail Lokoshchenko for the first time has acquired long-term average annual quantitative measures of the dry island for Moscow. In recent years the relative humidity in the capital is, in average, 3% (for city center - even 9%) lower than in the Moscow region. The scientist has also studied the centennial changes in the humidity parameters in Moscow. The relative humidity in Moscow significantly decreased during the last 146 years unlike water vapor pressure - another index of the atmospheric moisture - which has remained approximately constant. This decrease in relative humidity is mostly due to the global climate warming, as well as due to the general increase in UHI intensity.
"The originality of the approach is that in this work for the first time the centennial dynamics of urban heat island has been studied, and, also for the first time, the phenomenon of urban dry island has been described in detail. In practice, statistically significant average evaluations of the difference in air temperature and humidity parameters in cities and rural areas are important. They can be used in energetics, medical climatology, urban design and development, urban geography. Refinement of these evaluations is also needed to increase the effectiveness of the systems of central heating, landscape gardening, artificial irrigation in cities, and for better construction design", - the scientist concluded.
In a nutshell, the climate in Moscow is gradually becoming not only warmer, but more dry as well.
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Journal
Journal of Applied Meteorology and Climatology