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)

Britta Stumpe; Benjamin Bechtel; Jannis Heil; Christoph Jörges; Anna Jostmeier; Fabian Kalks; Katharina Schwarz; Bernd Marschner

doi:10.1016/j.scitotenv.2023.165228

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)

Sci Total Environ. 2023 Nov 1:897:165228. doi: 10.1016/j.scitotenv.2023.165228. Epub 2023 Jul 5.

Authors

Britta Stumpe¹, Benjamin Bechtel², Jannis Heil³, Christoph Jörges⁴, Anna Jostmeier⁵, Fabian Kalks⁶, Katharina Schwarz³, Bernd Marschner⁷

Affiliations

¹ Department of General Geography/Human-Environment Research, Institute of Geography, University of Wuppertal, 42119 Wuppertal, Germany. Electronic address: stumpe@uni-wuppertal.de.
² Bochum Urban Climate Lab (RUB), Geographical Institute, Ruhr-University Bochum, Universitaetsstr. 150, 44780 Bochum, Germany.
³ Criminological Research Department of the State Office of Criminal Investigation North Rhine-Westphalia, Voelklinger Str. 49, 40221 Düsseldorf, Germany.
⁴ VISTA Remote Sensing in Geosciences GmbH, Gabelsbergerstr. 51, 80333 Munich, Germany.
⁵ Department of General Geography/Human-Environment Research, Institute of Geography, University of Wuppertal, 42119 Wuppertal, Germany.
⁶ Department of Environment, Climate, Energy and Agriculture, Neuenfelder Straße 19, 21109 Hamburg, Germany.
⁷ Department of Soil Science and Soil Ecology, Geographical Institute, Ruhr-University Bochum, Universitaetsstr. 150, 44780 Bochum, Germany.

PMID: 37419369
DOI: 10.1016/j.scitotenv.2023.165228

Abstract

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.

Keywords: Green cooling potential; Land surface temperature; Soil hydraulic conductivity; Soil texture; Surface urban heat island; Urban green spaces.