Estimating Future Irrigation Requirements of Urban Green Infrastructure under Climate Change

Climate change poses an increasing challenge to the sustainable management of urban green infrastructure. Rising air temperatures, changing precipitation patterns and an increasing frequency and intensity of droughts lead to greater water stress for urban vegetation and consequently a higher demand for irrigation. Urban green infrastructure can only provide its multifunctional ecosystem services, such as cooling, when sufficient water is available. This highlights the importance of reliably assessing future irrigation requirements. This work presents a methodological framework for the spatial and temporal estimation of irrigation requirements for urban green infrastructure under current and future climatic conditions.

The presented approach is based on a quantitative assessment of irrigation deficit, which is defined as the difference between the water demand of the vegetation and the amount of effective precipitation. The methodological framework integrates evapotranspiration-based, vegetation-ecological and hydrological components, following established scientific approaches [1]. Reference evapotranspiration is calculated using the Hargreaves equation. Additionally, the study systematically assesses scenario-based changes in irrigation demand resulting from alternative urban green infrastructure development pathways.

Vegetation-specific water demand is estimated using the landscape coefficient approach. For this purpose, specific landscape coefficients were derived for typical types of urban green infrastructure, integrating the effects of vegetation type, planting density, and water stress into a multiplicative coefficient. This enables a differentiated representation of the variety of vegetation structures and management strategies found in urban green spaces. Natural water supply is accounted for by estimating effective precipitation using the NRCS Curve Number method, which characterizes runoff and retention processes in urban areas and quantifies the proportion of precipitation available within the root zone.

The spatial implementation is carried out within a grid-based framework with a spatial resolution of 100 m × 100 m across three case studies. Within each grid cell, the proportions of different vegetation types, the associated normalized difference vegetation index (NDVI), land use information, and soil parameters are compiled. Area-weighted vegetation coefficients and hydrological parameters are then aggregated to the grid areas, which serve as the basis for irrigation calculations.

Analyses are performed for a historical reference period (1991–2020) and a future period (2031–2060) under different climate change scenarios (RCP2.6, RCP4.5, and RCP8.5). This allows a systematic evaluation of climate-driven changes in irrigation requirements. The results are evaluated monthly and visualized using box plots to illustrate changes in irrigation requirements and associated uncertainties. The results show a potential increase in irrigation demand in the case studies, with scenario-specific differences. In addition, the influence of different developments in green infrastructure on irrigation requirements is highlighted.

Overall, the developed methodology provides a scalable, integrated, and scientifically robust tool for assessing the irrigation requirements of urban green infrastructure.

Acknowledgements: The presented research is funded by the Federal Ministry for Agriculture and Forestry, Climate and Environmental Protection, Regions and Water Management Republic of Austria

References:

• Cheng, H.; Park, C.Y.; Cho, M.; Park, C. Water Requirement of Urban Green Infrastructure under Climate Change. Science of The Total Environment 2023, 893, 164887, doi:10.1016/j.scitotenv.2023.164887.