Spatial structure and temporal variability of a surface urban heat island in cold continental climate

Warm urban climate anomalies are a challenging problem for city’s economy and ecology. This problem is even more pressing in boreal environment with its sensitive ecosystems and considerable anthropogenic urban heat flux. The boreal regions of Eurasia witness both rapid urbanization and accelerated regional warming in the twenty-first century. Still, local climate of boreal cities is only fragmentary studied. There were no studies addressing spatial and temporal variability of urban temperature anomalies in Eurasian cities with cold continental climate. There were many indirect reports indicating large temperature anomalies and longer growing season in boreal cities. This study considered a land surface temperature (LST) anomaly, frequently referred to as a surface urban heat island (SUHI), in a typical young mid-size boreal city of Nefteyugansk. This city exemplifies urban planning and energy use patterns of a pleiad of cities in this oil and gas region of northern West Siberia. The study is based on LST products from the MODerate resolution Imaging Spectro-radiometer (MODIS) onboard of the Terra and Aqua satellite platforms. The MODIS data for 14 years (2001–2015) were processed to reveal geographical extent and diurnal variations of the SUHI in summer (June, July, August) and winter (December, January, February) seasons. The study found that the mean annual SUHI has higher LST than the surrounding natural background by + 2.4 K. Considering the meridional temperature gradient in this region, such a strong SUHI makes the urban climate similar to climate found 600 km south of the city. The diurnal mean summer (+ 2.1 K) and winter (+ 2.4 K) SUHI intensities are rather similar in Nefteyugansk. The daytime (+ 2.1 K) and nighttime (+ 2.5 K) SUHI intensities are also similar in wintertime. In summertime, however, the daytime SUHI intensity (+ 3.3 K) is significantly larger than that in nighttime (+ 1.0 K). There is also larger interannual variability of the SUHI in the summer season, especially in nighttime. The SUHI statistics in Nefteyugansk discerns this cold continental city from previously studied cities in the temperate climate zone. Heating of apartment and industrial buildings maintains a large anthropogenic heat flux in the city (estimated to be on average of 15–20 W m−2) and therefore supports the persistent winter SUHI. Weak turbulent mixing in the stably stratified lower atmosphere traps the heat in the urbanized area. This study found that the SUHI footprint in Nefteyugansk is considerably (two to three times) larger than the area of the city proper itself.