Abstract
The climate, soil properties, groundwater depth, and surrounding settings in cities vary to a tremendous extent, which all lead to different growing conditions and health for street trees. Because of climate change, the availability of water in cities will undergo changes in the next decades. As urban trees have a very positive influence not only on microclimate but also on biodiversity and life quality in general, they need to be protected. Thus, we need to know how to measure and calculate the availability of water for street trees to optimize their site conditions and water supply. This study presents Hydro-Pedo-Transfer Functions (HTPFs) for predicting water supply and actual evapotranspiration of street trees for varying urban conditions. The HTPFs are easy to use, and the input parameters can either be mapped easily or taken from local climate agencies or soil surveys. The first part of the study focuses on the theoretical background and related assumptions of the HTPFs for predicting water supply, and on obtaining the potential and actual evapotranspiration of urban street trees using easily available data. The second part gives information and exemplifies how this input data can be measured, mapped, or predicted. Calibration of the HTPFs were done using the sap-flow measurements of three Linden trees (Tilia cordata). Exemplarily, the HTPF scenarios for the varying urban site conditions of Berlin are presented. The water supply and actual evapotranspiration of the street trees severely depend on the local climate (summer rainfall and potential evapotranspiration), site conditions (catchment area, soil available water, and degree of sealing), and on the tree characteristics (species, age, and rooting depth). The presented concept and the equations build a good and flexible frame that is easy to program using a spreadsheet tool or an R script. This tool should be tested and validated also for other cities and climate regions.
Highlights
This paper investigates so-called Hydro-Pedo-Transfer Functions (HPTFs) as a potential tool to better inform about water supply and water stress for individual trees in cities, such as Berlin
Eo,s in Equation (8) can be calculated by a simple linear regression equation relating the FAO grass reference evapotranspiration of the summer half-year
To test the concept and to calibrate the actual evapotranspiration predictions, both sap-flow measurements from two Linden trees and street site mappings were done in Berlin from 2017 till 2020
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Cated by massive deadwood development, fundamental deterioration in vitality, and inNot least, unsealed vegetated sites, such as urban greenery and street trees, can reduce dividual tree mortality [19] In both years, 2018 and 2019, the State of Berlin spent an adrunoff, after stormwater events, which is of high importance in urban areas [14]. Severe damage to the entire Berlin tree population occurred, indicated spiration), soil (water retention and groundwater and deterioration tree (species,inage, rooting by massive deadwood development, depth), fundamental vitality, and individual tree mortality [19] In both years, 2018 and 2019, the State of Berlin spent an additional. In cities of arid and semi-arid regions, street trees are important for cooling the air temperature by transpiration and shading They are essential for the quality of life. It became an essential issue to develop new strategies for greening inner-city places and planting new trees
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