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

Authors: Victoria Miles and Igor Esau at the Nansen CenterAuthors: Victoria Miles and Igor Esau at the Nansen CenterWarm 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.

- Up to our knowledge, the first study of the long-term variability of the surface urban heat island in a cold climate city has been published, Igor Esau and Victoria Miles say. The researchers from the Nansen Center are two of the authors behind the paper in Springer Nature and supported by Belmont Forum and Norwegian Research Council project “Anthropogenic Heat Islands in the Arctic: Windows to the Future of the Regional Climates, Ecosystems, and Societies” (no. 247468). 

- 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, Esau says. 

Knowledge on spatial and temporal variability of urban temperature anomalies is essential to support more efficient urban planning and management. The mean land surface and air temperatures are climate parameters that enter into urban planning and construction standards. However, the national standards for construction norms and regulations are based on regional climate data or meteorological observational networks that are located mostly outside the urban center and do not account urban temperature anomalies.

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 group 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.

- Nefteyugansk is a middle size city in a cold (boreal) continental climate. The mean winter surface heat balance in this region is negative. However, our analysis of the MODIS LST reveals persistent positive temperature anomalies collocated with the urban surfaces, Miles tells.

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.

Figure 2: The 14-year (2001–2014) climatology of the MODIS LST in Nefteyugansk for summer and  winter seasons. The color shading shows the mean seasonal temperatures. The urban contours were obtained from a LandSAT-8 image.Figure 2: The 14-year (2001–2014) climatology of the MODIS LST in Nefteyugansk for summer and winter seasons. The color shading shows the mean seasonal temperatures. The urban contours were obtained from a LandSAT-8 image.

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.

- Our findings emphasize that urban climate considerably differs from the corresponding regional climate. In practice, however, the use of the urban climate information remains rather limited, says Esau and Miles. The two researchers are referring to a study of Swedish cities by Eliasson (2000) revealed that urban planners were interested in climate information but did not use it systemically. - Accessible and detailed information from remote sensing products might change the attitudes of urban managers. There are no doubts that intensive dialog between climatologists and urban planners is needed to improve environmental services in cities, Esau and Miles conclude. 

Citation:

Igor Esau1 & Victoria Miles1 & Mikhail Varentsov2,3 & Pavel Konstantinov2 & Vladimir Melnikov4,5,. Spatial structure and temporal variability of a surface urban heat island in cold continental climate. Theoretical and Applied Climatology (2019). https://doi.org/10.1007/s00704-018-02754-z

Figure 3: The seasonally averaged SUHI intensity in Nefteyugansk for summer and winter seasons for the considered 14 years (2001–2014).Figure 3: The seasonally averaged SUHI intensity in Nefteyugansk for summer and winter seasons for the considered 14 years (2001–2014).