Determinants of Evapotranspiration in Urban Rain Gardens: A Case Study with Lysimeters under Temperate Climate

Ahmeda Assann Ouédraogo,Brigitte Durand,Marie-Christine Gromaire,Emmanuel Berthier

doi:10.3390/hydrology9030042

Abstract

Accurate evaluation of evapotranspiration (ET) flux is an important issue in sustainable urban drainage systems that target not only flow rate limitations, but also aim at the restoration of natural water balances. This is especially true in context where infiltration possibilities are limited. However, its assessment suffers from insufficient understanding. In this study, ET in 1 m3 pilot rain gardens were studied from eight lysimeters monitored for three years in Paris (France). Daily ET was calculated for each lysimeter based on a mass balance approach and the related uncertainties were assessed at ±0.42 to 0.58 mm. Results showed that for these lysimeters, ET is the major term in water budget (61 to 90% of the precipitations) with maximum values reaching 8–12 mm. Furthermore, the major determinants of ET are the existence or not of an internal water storage and the atmospheric factors. The vegetation type is a secondary determinant, with little difference between herbaceous and shrub configurations, maximum ET for spontaneous vegetation, and minimal values when vegetation was regularly removed. Shading of lysimeters by surroundings buildings is also important, leading to lower values. Finally, ET of lysimeters is higher than tested reference values (evaporimeter, FAO-56, and local Météo-France equations).

Highlights

Urbanization has a great impact on cities’ hydrological cycle: runoff is increased to the detriment of infiltration and evapotranspiration (ET), leading to an increase in risks linked to flooding and deterioration of the receiving environments
Significant hydrological processes in a rain garden in‐ clude the exfiltration to the underlying soil or by drainage system, the evapotranspiration and the interception from vegetation
The high value of the lysimeter with an internal water storage (IWS) compared to what is found here could be explained by the focalised summer period, by the size of the IWS, which is larger in the Wadzuk case (36 cm), by the evaporative demand, and the inputs to the lysimeter

Summary

Introduction

Urbanization has a great impact on cities’ hydrological cycle: runoff is increased to the detriment of infiltration and evapotranspiration (ET), leading to an increase in risks linked to flooding and deterioration of the receiving environments. Urban stormwater management policies have been developed in recent years that favour runoff manage‐ ment in green infrastructure systems (GIS) in order to store the water before to infiltrate, evaporate and transpirate it. These sustainable urban drainage systems (SUDS) are con‐ sidered as a viable mechanism that can substitute or complete the traditional sewerage system (canalisation, underground basins, pipes, etc.) and provide environmental benefits apart from hydraulic services [1,2,3,4]. These processes “should work together” for being able to control large flows and reduce the total volume of small storms [9]

Methods

Results

Discussion

Conclusion