Measurements of Evaporation in Urban area: A Comparison of two soil sealing types

Paved surfaces are a necessary infrastructure of cities, traditionally they are designed to carry vehicular, pedestrian traffic and transport products, and they provide public spaces for social communication. These paved surfaces also function as channels for waste matter, sewage, gas and electrical and as transport processes of water, matter, and energy between the soil and atmosphere in urban areas. In other hand, their characteristics lead to an altered hydrological balance compared to rural counterparts.

This study aimed to gain new insights into urban hydrological balance, in particular, the evaporation from paved surfaces. Hourly data of evaporation obtained from two high-resolution weighable lysimeters, these lysimeters are covered in two pavement sealing types commonly used for sidewalks in Berlin: cobblestones and concrete slabs. Soil volumetric water content and soil temperature of sandy soil was measured in the lysimeters with capacitance soil moisture sensors at 5cm depth. Moreover, time series consisted of hourly measurements climatology observations was obtained by climate station located near to the lysimeters. The measurements started in June 2016 and have been carried out for one year.

The data could be paired to estimate the variation of evaporation and how it was affected by cobblestones and concrete slabs and environmental factors.  In this case, a generalized additive model (GAM) for each sealing type was built, where the model response was the difference between the paired samples of evaporation from cobblestones and concrete slabs and the explanatory variables were the observations from the climate station and lysimeter data according to each sealing type. The statistical model tries to explain how the explanatory variables are related to a higher or lesser difference in evaporation between the two surfaces. As the result, the modelling approach showed that the evaporation from cobblestones tends to be higher than concrete slabs when the air temperate and soil temperature at 5 cm depth increases. The evaporation from cobblestone was also higher when the relative humidity was low, while the evaporation from concrete slabs was higher than cobblestones when the relative humidity was between 50 - 75%. When the relative humidity was higher than 75% the model showed that there was no difference in evaporating between the two sealing types.  The model showed also that the evaporation from concrete slabs tends to be higher than cobblestones when the solar radiation increases. Moreover, when the cumulative precipitation data in 9-hour intervals was higher than 10mm the cobblestone evaporates more than concrete slabs.