Quantifying the cooling-effects of urban and peri-urban wetlands using remote sensing data: Case study of cities of Northeast China

World urbanization has been increasing at a rapid pace over the past few decades, particularly in developing countries. The urban heat island (UHI) effect, which occurs during rapid urbanization, profoundly affects human life and health. The cooling-effect (CE) of urban wetlands can effectively mitigate the impact of UHI. In this study, we estimated the intensity of UHI and quantitatively assessed the CE of urban wetlands in cities of northeast China by using split-window algorithm (SWA) to estimate land surface temperatures (LST) from Landsat-8 TIRS. We used correlation analysis to examine the relationships between characteristics of wetlands and surrounding buildings and two cooling-effect indices: normalized cooling capability index (NCCI) and normalized cooling efficiency index (NCEI). Our results have shown that the cooling-effect of rivers is much higher than that of other wetlands types and green spaces. The average NCCI of wetlands is 42.3 times higher than that of green spaces. A strong positive relationship exists between the cooling capability of urban wetlands and the area, shape and hydrologic connectivity of wetlands. Wetlands with more complex shape have better cooling-effect. The average NCCI of wetlands connected to other surface waters six times higher than that of isolated wetlands. There is a negative relationship between the cooling capability of urban wetlands and height and density of surrounding buildings. These findings are helpful for designing urban wetlands and for urban planning to minimize the potential environmental impacts of UHI.