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Journal Article

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


Ament,  Felix
B 5 - Urban Systems - Test Bed Hamburg, Research Area B: Climate Manifestations and Impacts, The CliSAP Cluster of Excellence, External Organizations;
Boundary Layer Measurements, The Land in the Earth System, MPI for Meteorology, Max Planck Society;

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Wiesner, S., Eschenbach, A., & Ament, F. (2014). Urban air temperature anomalies and their relation to soil moisture observed in the city of Hamburg. Meteorologische Zeitschrift, 23(2), 143-157. doi:10.1127/0941-2948/2014/0571.

Cite as: https://hdl.handle.net/11858/00-001M-0000-0019-B412-C
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 + 1.0K$+1.0\,\text{K}$ for inner city sites and + 0.25K$+0.25\,\text{K}$ to - 0.2K$-0.2\,\text{K}$ for suburban sites compared to a rural reference. The nocturnal urban heat island (UHI) is identified and averages + 1.7K$+1.7\,\text{K}$ at the inner city stations, + 0.7K$+0.7\,\text{K}$ at a suburban district housing area and + 0.3K$+0.3\,\text{K}$ at a nearby green space. The observed UHI effect is most prominent when the wind speed is low (≤ 2ms-1$\leq2\,\text{ms}^{-1}$) and the sky is only partly cloudy (≤ 6∕8th$\leq6/8^{\text{th}}$). In spring 2011 an average inner city UHI of up to + 5.2K$+5.2\,\text{K}$ 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 - 0.5K$-0.5\,\text{K}$ above unsealed, vegetated surfaces from a sealed site during days with a turbulent mixing induced by wind speed > 2ms-1$>2\,\text{ms}^{-1}$. 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.