How Cool Are Allotment Gardens? A Case Study of Nocturnal Air Temperature Differences in Berlin, Germany

Annemarie Tabea Rost,Corinna Seidel,Fred Meier,Daniel Fenner,Marco Otto,Victoria Liste,Lea Matscheroth

doi:10.3390/atmos11050500

Abstract

Urban green infrastructures have been extensively studied for their ability to mitigate the urban heat island (UHI) effect. However, allotment gardens (AGs)—a prominent type of urban green infrastructure within many European cities—have not yet been comprehensively investigated concerning their microclimates. In this study, nocturnal air temperatures ( T N ) in 13 AG complexes (AGCs) were measured during the summer of 2018 in Berlin, Germany. These were compared to measurements in densely built-up urban areas (URB), two large inner-city parks and rural areas (RUR). On average, the assessed AGCs were 2.7 K cooler at night than URB. Most of the investigated AGCs (11/13) displayed a larger mean T N difference to URB ( Δ T N A G C ¯ ) than the examined urban parks. RUR showed the largest differences to URB ( Δ T N R U R ¯ ), indicating a UHI effect. Furthermore, the influence of land surface characteristics of the AGCs on Δ T N A G C ¯ was analyzed. Δ T N A G C ¯ decreased significantly as the floor space index around AGCs increased. The analysis of the shape complexity also produced a significant positive correlation with Δ T N A G C ¯ . In contrast, size and distance to the city center of an AGC decreased significantly with increasing Δ T N A G C ¯ . This study provides first insights into the microclimate of AGs and influencing variables concerning T N .

Highlights

The distinctive features of urban areas [1] result in an altered energy exchange compared to their rural surroundings
allotment gardens (AGs) represent an important part of urban green infrastructure [37] and show differences to urban parks
All ∆T for each night (TN) allotment garden complexes (AGCs) and ∆TN RUR are statistically significant across all nights (p ≤ 0.05), but not during nights with calm and clear weather conditions

Summary

Introduction

The distinctive features of urban areas [1] result in an altered energy exchange compared to their rural surroundings. Urban areas are characterized by a lower albedo, higher thermal conductivity and higher heat capacities of building materials [2] They show reduced convective cooling, as well as lower evapotranspiration rates [2]. UHI intensity, defined as the difference in T between the city and the surrounding rural area, varies in time and space It is influenced by seasons, time of day, meteorological, geographical and physical properties. The UHI effect is especially prominent during nights with calm and clear weather conditions [7,8] Under these conditions, the energy budget of the canopy layer can be simplified to be primarily determined by the outgoing longwave radiation [7,8]. Large green spaces are found to mitigate the UHI effect at night [11]

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Conclusion