Soil texture mediates the surface cooling effect of urban and peri-urban green spaces during a drought period in the city area of Hamburg (Germany)

• Published in: The Science of the total environment 2023-11, Vol.897, p.165228-165228, Article 165228
• Main Authors: Stumpe, Britta, Bechtel, Benjamin, Heil, Jannis, Jörges, Christoph, Jostmeier, Anna, Kalks, Fabian, Schwarz, Katharina, Marschner, Bernd
• Format: Article
• Language: English
• Subjects: Green cooling potential; Land surface temperature; Soil hydraulic conductivity; Soil texture; Surface urban heat island; Urban green spaces
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2023.165228

Urban green spaces (UGS) and peri-urban green spaces (P-UGS) play a crucial role in reducing the land surface temperature within the urban environment, especially during heat waves. Although their cooling effect generally is due to shading and evaporation, the role of soil texture and soil water availability on surface cooling remains largely unexplored. This study investigated the impact of soil texture on the spatio-temporal patterns of LST in different UGSs and P-UGSs in Hamburg (Germany) during a hot summer drought period. The LST and the Normalized Differentiated Moisture and Vegetation Indices (NDMI, NDVI) were calculated based on two Landsat 8 OLI/TIRS images from July 2013. Non-spatial and spatial statistical approaches such as stepwise backward regression or Hotspot (Getis-Ord Gi*) analyses were applied explaining LST distributions in relation to soil texture within each UGS and P-UGS. All GSs were clearly characterized as surface cooling islands whereas, for each GS, an individual thermal footprint was observed. Within all GSs, the LST patterns showed a significant negative relationship to NDMI values, whereas the NDVI values and the elevation were of minor importance. Soil texture was found to influence the LST distribution significantly in most UGSs and P-UGSs, where sites on clay-rich soils showed the highest LST values compared to sites on sand- or silt-rich soils. For example, in parks, clayey soils showed a mean LST of 25.3 °C whereas sand-dominated sites had a mean LST of only 23.1 °C. This effect was consistent throughout all statistical approaches, for both dates and across most GSs. This unexpected result was explained by the very low unsaturated hydraulic conductivity in clayey soils which limits plant water uptake and transpiration rates responsible for the evaporative cooling effect. We concluded that soil texture has to be considered for understanding and managing the surface cooling capacity of UGSs and P-UGSs. [Display omitted] •UGS and P-UGS show different thermal footprints.•Spatial patterns of LST, NDVI and NDMI are related to soil texture.•LST patterns are mainly controlled by NDMI, less by NDVI.•Soil texture affects plant water availability and the cooling effect of vegetation.•Very low hydraulic conductivity restricts water availability on clay-rich soils.