Evapotranspiration of Technical Substrates – Methodology for Calculating Evapotranspiration of Technical Substrates

Abstract

The existing formulae, like the well-known Penman-Monteith equation, used for calculating evapotranspiration are characterized by great differences concerning their results. These differences stem from the diversified climatic conditions and vegetation specifics during their development. Every formula of evapotranspiration only delivers 100% correct results, if it is used under the same climatic condition it was developed in. Therefore, a new method for calculating evapotranspiration via specific, but comparatively easily established formula was presented. After a theoretical introduction for illustrating some fundamental aspects for this work, the test setup and approach for creating these formulae are described in detail. The test set up considers typical climatic conditions and simulates, for example, the average temperature of Vienna, a summer day and an extremely hot day. While using a polynomial correlation, a formula for calculating evapotranspiration at any temperature is possible. For determining the evapotranspiration rate (in mm/m² per 24 hours day) due to the presented formula, only temperature, sort of vegetation and technical soil has to be defined. As a result, the relevance of this work is the presentation of a method to determine the evapotranspiration of any technical substrates (used for e.g. green roofs, façade greenery, indoor greenery, raingardens…) with or without any kind of vegetation, while using the created formula.

Equation for Calculating Evapotranspiration of Technical Soils for Urban Planting

“…Three main steps were necessary to create the new equation for calculating evapotranspiration. The first and second step were described in a previous paper by Weiss et al [19]. Information about test set-up and the test series in the climate chamber were described in detail.…”

“…Three repetitions were performed for each technical soil and plant in each of the three climate scenarios. Overall, there were nine values of evapotranspiration for each technical soil and plant, which were inserted in the polynomial trend line [19].…”

“…The test set-up is already described in detail in the paper "Evapotranspiration of Technical soils-Methodology for calculating evapotranspiration of technical soils" [19]. Here, a short summary of the test set-up is given once more for a better understanding of the processes, which led to the equation for calculating evapotranspiration.…”

“…Afterwards, the containers had to drip off for another two hours (instead of four hours as described in Green Roof Guidelines [41]). After the whole procedure, which lasts four hours in total, the plant containers were placed on the load cells in the climate chamber [19].…”

“…Therefore, a very important field of application for evapotranspiration equations is rainwater management in urban areas. A large variety of different equations for calculating evapotranspiration exists, as already explained in-depth in the publication "Evapotranspiration of Technical soils-Methodology for calculating evapotranspiration of technical soils" [19]. Existing equations, such as the most famous combination equation by Penman [20], only delivers 100% correct results in conditions (such as vegetation, natural grown soil, climatic conditions, etc.)…”