Cooling the City of Warsaw: Thermal Insights From Vistula River Valley

ABSTRACT The study aimed to investigate thermal conditions in one of the largest river valleys in Europe, the Vistula River valley, in a section of the capital city, Warsaw. The research is based on comparing a 6‐year series of 10‐min air temperature measurements from eight sites: three located in different sections of the Vistula Valley, three others situated in built‐up areas further from the river, one in the city centre and one at the outskirts—it is a network created specifically to analyse thermal conditions in the valley, as no standard meteorological stations exist there. The analysis reveals an almost 24‐h cooling effect of the Vistula. The air temperature differences between the valley and the city centre were greatest in summer, with average differences of up to 4°C, whereas the yearly average was 1.2°C–1.3°C. Regardless of the season, the valley was cooler than the city centre between 5 PM. and 5 AM. The cooling effect rises to 0.5°C during heat waves compared to other summer days. Nearly all differences between the cooler valley and city build‐up areas are statistically significant at the p < 0.001 level. The thermal cold spot (TCS) effect, analysed based on 25 land surface temperature images, was most frequent in the central part of the valley (in 65.2% of images), followed by the north (52.6%) and least frequent in the southern section (36.0%), whereas, at nearby built‐up sites, the frequency was less than 10%. The range of the effect was widest in the downtown part of the valley, almost 997 m. These findings offer novel insights into the impact of large rivers and their surroundings on urban thermal environments. As global warming and urban heat island intensity increase worldwide, the role of river valley climates in adaptation policies is also expected to grow.