A new approach to study the long-term urban heat island evolution using time-dependent spectroscopy

Urban Climate. 2021. Vol. 40. Article 101026.

Varentsova S., Mikhail I. Varentsov

This study presents a new approach to study long-term temperature and urban heat island intensity (UHII) evolution based on the method of time-depended spectroscopy on the example of Moscow megacity. In contrast to standard spectroscopy, this method allows analyzing the changes of the amplitude Fourier spectrum of the time series along the study period. Applying the novel method to the air temperature series for the period of 1977-2020, we demonstrate that ongoing changes of the mean temperature and UHII are accompanied by the changes of their spectra, including the spectral amplitudes corresponding to diurnal, annual and synoptic-scale oscillations. Such changes are complex, often non-linear, and seasonally asymmetric. Steady upward trends are found for summer season, for the spectral amplitudes of diurnal temperature and UHII oscillations, and synoptic-scale UHII oscillations. Spectral amplitudes of annual temperature and UHII oscillations experiences V-shaped dynamics with an increase since 1990th. For UHII such pattern reflects a switch between regimes with wintertime or summertime UHI maximum. Presented results provides an evidence that observed intensification of Moscow's UHI is forced not only by urban growth, but also by changing background meteorological conditions, which are becoming more favorable to UHI appearance in summer and less favorable in winter.

Keywords: Urban heat island, spectral analysys, Fourier spectrum