Summer season soil temperature conditions, and soil moisture properties on the extensive green roofs in Oslo, Norway
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Nowadays, green roofs have been investigated more and more in order to improve the quality of municipal environment particularly to reduce the urban heat island effect and storm water runoff. Soil temperature and soil moisture are therefore two key factors in this respect. They should also be considered as important elements for plant distribution and community composition on extensive green roofs. The aim of this study is to investigate summer season soil temperature conditions, and soil moisture properties on extensive green roofs in Oslo. The study has been performed on 37 plots on 17 extensive green roofs. Soil temperatures were recorded by data loggers 2cm under the soil surface, four times during a day. Soil moisture was determined through dry and moist weight, and porosity after extracted by PVC cylinders. The relationship between soil temperature parameters and soil moisture factors with vegetation cover, also between soil temperature and soil moisture were tested by Principle Component Analyses, regression and correlation analyses, and box plot. The statistical results indicate that vegetation abundance is highly negatively correlated with soil temperature variables and positively correlated with saturated soil moisture and field capacity porosity. The results of the soil temperature measurements demonstrate that apart from two roofs, soil temperatures have been in an optimum range. The analyses also proved that soil temperatures will be increased or decreased with soil moisture content, demonstrating the interaction of soil temperature and soil water availability.