Assessment of the thermal capacity of urban parks to mitigate the urban heat island in the main cities in Romania

It is well known that urban parks cause a cooling effect on the urban climate and have a decisive role in the formation of the Park Cool Island (PCI) effect. Urban parks can help lower the Land Surface Temperature (LST), and consequently mitigate the effects of the Surface Urban Heat Island (SUHI).
Parks in Romanian cities vary in size, shape, vegetation density, and configuration, all of which influence their ability to produce a cooling effect. In the current study, various parks in Romania's major cities have been investigated to understand their capacity to locally alleviate/buffer the UHI effect and contribute to more comfortable thermal urban environments. In the present study, we also aimed to develop an algorithm to classify the cooling efficiency of parks. This algorithm incorporates various aspects, such as urban metrics (distance to the center of the urban heat island or UHI boundaries, distance to the center of densely built-up areas), urban built-up conditions (areas with extensive impervious surfaces, paved, asphalted, and concreted areas), or urban land cover (the percentage of the total area occupied by water bodies, wooded, grassed areas). 
To be able to extract the percentage of the total area occupied by wooded, grassed, paved, asphalted, and concreted areas, a number of biophysical indices that aim to evaluate the amount of urban vegetation or the percentage occupied by different types of natural or artificial surfaces were used, such as the NDVI (Normalized Difference Vegetation Index), SAVI (Soil Adjusted Vegetation Index), LAI (Leaf Area Index), NDII (Normalized Difference Impervious Index), NDBI (Normalized Difference Building Index).
Overall, the analysis of multiannual Land Surface Temperature (LST) data extracted from Landsat 8-9 thermal bands in summer 2024 reveals that Romanian urban parks generally exhibit cooler and more stable thermal profiles compared to surrounding urban areas. The thermal difference between the different urban parks and the surrounding urban areas ranged between 1.5-3.5°C. This significant variation in the cooling effect depends strongly on the position of the parks within the urban landscape and the relation to the UHI boundaries (quasi-central, peripheral, or bordering), the compositional (ratio of green or artificial surfaces), and configurational (area, shape index) characteristics and tree density.
Parks with a quasi-central position in the urban landscape, with an area of more than 30 ha, a percentage of green areas of more than 70%, a rounded or slightly rectangular shape, and a high tree density generated the most substantial cooling effects, with temperature differences of up to 3.5-4 °C. The analyzed urban parks also generate a temperature gradient effect, whereby temperatures gradually rise as one moves away from the park into the surrounding urban environment. As a key finding, we outline that in Romanian cities, the cooling effect on air temperature decreases by approximately 1.3-1,6°C per 10 meters from the park's edge. 
    In conclusion, this research demonstrates the vital role of urban parks in mitigating UHI effects in Romania's main cities, emphasizing the need for strategic urban planning that maximizes their cooling potential.