Annette Eschenbach

Urban air temperature anomalies and their relation to soil moisture observed in the city of Hamburg

The spatial variability of the urban air temperature for the city of Hamburg is analyzed based upon a one-year dataset of meteorological and pedological measurements. As local air temperature anomalies are subject to land-use and surface cover, they are monitored by a network of measurement stations within three different urban structures. Mean annual temperature deviations are found to be +1.0 K for inner city sites and +0.25 K to −0.2 K for suburban sites compared to a rural reference. The nocturnal urban heat island (UHI) is identified and averages +1.7 K at the inner city stations, +0.7 K at a suburban district housing area and +0. 3K at a nearby green space. The observed UHI effect is most prominent when the wind speed is low (≤ 2m s −1 )a nd the sky is only partly cloudy (≤ 6/8 th ). In spring 2011 an average inner city UHI of up to +5.2 K is observed during situations matching these conditions, while the extraordinary dry fall of 2011 lead to remarkably high air temperature differences at all observed stations. As expected, no evidence for a significant impact of topsoil moisture on nighttime UHI effect is found. The analysis of air temperature anomalies during daytime results in an annual mean deviation of −0.5 K above unsealed, vegetated surfaces from a sealed site during days with a turbulent mixing induced by wind speed > 2m s −1 . Here, there is an indication for a relation between the water content of upper soil layers and the warming of air: 11 to 17 % of the variance of the diurnal air temperature span is found to be explained by the soil water content for selected relevant days.

Spatial and temporal variability of urban soil water dynamics observed by a soil monitoring network

PurposeUrban soils’ variability in the vertical direction presumably affects hydrological parameters at the timescale. Moreover, horizontal soil alterations at small spatial scales are common in urban areas. This spatio-temporal variability and heterogeneity of soil moisture and the possible influencing factors were to be described and quantified, using data of a soil monitoring network in the city of Hamburg, Germany.Materials and methodsSoil moisture data from ten observation sites within the project HUSCO was evaluated for two different years. The sites were located within districts with different mean groundwater table depths and characteristic urban soil properties. Soil hydrological simulations with SWAP were calculated for a selected site.Results and discussionThe temporal evolution of soil water content and tension for the sites was very distinct, related to soil substrate, organic matter content, and groundwater table depth. Impacts of different vegetation rooting depths, the soil substrates’ type, and to some extent the degree of disturbance on soil water dynamics could be identified. An impact of groundwater table depth on the water content of the topsoil during low-precipitation periods could be assumed. The comparison of the results of soil hydrological simulations with empirical data indicated an overestimation of infiltration and percolation for the given soil substrates.ConclusionsWhile soil properties are mainly determinant for the long-term progression of soil hydrology, local site factors affect the short-term regime. A shallow groundwater table contributes to more constant water dynamics while the relative decrease of water during a dry phase is diminished.

Terrestrische und semiterrestrische Ökosysteme

Die Metropolregion Hamburg (MRH) erstreckt sich auf einer Gesamtflache von ca. 26.000 km2 uber insgesamt 19 (Land-)Kreise/kreisfreie Stadte in den Bundeslandern Hamburg, Schleswig-Holstein, Mecklenburg-Vorpommern und Niedersachsen. Entsprechend vielgestaltig sind die naturraumlichen Verhaltnisse, die im Hinblick auf die Landschaftsentwicklung masgeblich durch die quartaren Vereisungen gepragt sind. Das Klima der MRH lasst sich in ein starker ozeanisch gepragtes in Kustennahe und in ein weniger ozeanisch gepragtes der sudostlichen Teilgebiete differenzieren. Die Zunahme kontinentaler Klimaeinflusse entlang eines von Nordwest nach Sudost verlaufenden Gradienten kommt u. a. in einer um 0,4 °C ansteigenden Jahresmitteltemperatur und einer von 831 mm/Jahr (Station Cuxhaven) auf 557 mm/Jahr (Station Luchow) zuruckgehenden Niederschlagsmenge zum Ausdruck (▶ Abschn. 2.2.3).