How can urban blue-green space be planned for climate adaption in high-latitude cities? A seasonal perspective

•A year-round analysis was conduct regarding the cooling extent, intensity, and efficiency of blue-green space.•The concept of the threshold value of efficiency (TVoE) was validated and calculated in different seasons.•The effect of temperature on TVoE was revealed, which deepens the understanding of the TVoE study.•The roles of blue and green (tree- and grass-covered) space on cooling effect in a high latitude city were analyzed.•The climate adaptive planning implications in high latitude cities were suggested. Climate change has increased the frequency of extreme climatic events and the intensity of heatwaves in high-latitude cities that have rarely been affected in the past, yet there is less attention to these regions. Therefore, we selected Copenhagen as the case, we used spatial/statistical methods to assess the cooling-effect of blue-green spaces in different seasons. We found (1) land surface temperature (LST) is negatively correlated with Normalized Difference Vegetation Index (NDVI) and Modified Normalized Difference Water Index (MNDWI) in all seasons; (2) Tree-covered greenspace with a compact shape would be a priority for climate adaption in high-latitude cities. While when the area of blue-green space is large to a certain extent (>1 ha), the complex shape also has a strong cooling-effect. Further, the area and cooling extent and intensity conform a logarithm function with significant correlations except for winter. (3) Compared with other seasons, blue-green space provides a higher cooling-effect in summer, and the mean cooling extent and intensity are 150 m and 2.47℃; (4) Background temperature can significantly affect the threshold value of efficiency (TVoE). The results of this study expand the understanding of the cooling-effect of blue-green spaces and provide implications for sustainable urban planning.