Lush green city with trees thriving using minimal water.

Urban Trees: Can the Right Choice Save Water and Help Cities Thrive?

Elliot Brynn in Climate & Environment June 2025 • 4 min read.

"Discover how selecting the best tree species can dramatically reduce urban water use and boost the sustainability of our cities."

As cities grow, the importance of urban green spaces becomes ever more critical. Urban trees provide a multitude of benefits, from improving air quality to cooling urban heat islands. However, these benefits come with a cost: water. In many urban environments, water scarcity is a growing concern, making it essential to choose tree species that can thrive with minimal water use.

New research sheds light on how different tree species in urban environments utilize water, revealing significant differences that can inform more sustainable urban planning. By understanding these variations, city planners and landscapers can make informed decisions about which trees to plant, optimizing water conservation efforts while maximizing the ecological and aesthetic benefits of urban forests.

This article delves into a study conducted in Bangkok, Thailand, examining the water use characteristics of common street trees. The findings offer valuable insights into how different species respond to seasonal variations and drought conditions, providing a foundation for strategic urban greening initiatives worldwide.

Why Tree Selection Matters: Unlocking Water-Wise Urban Forestry

Lush green city with trees thriving using minimal water.

The study in Bangkok focused on three commonly planted tree species: Pterocarpus indicus (Pi), Swietenia macrophylla (Sm), and Lagerstroemia speciosa (Ls). These species were selected because they exhibit different leaf phenologies—the timing of their leaf growth and fall—and vary in their prevalence within the city. Researchers investigated how these trees responded to different levels of soil moisture and atmospheric water deficit, providing a comprehensive understanding of their water use behaviors.

Researchers monitored sap flux density of trees, using sophisticated sensors, under well-watered conditions and during induced drought periods. They looked at how trees adjust water use as conditions changed. This study provides invaluable insights to which species will thrive in the face of water stress.

Pterocarpus indicus (Pi): Semi-evergreen species.
Swietenia macrophylla (Sm): Evergreen species.
Lagerstroemia speciosa (Ls): Deciduous species.

The results indicated that semi-evergreen and evergreen species (Pi and Sm) exhibited more consistent water use patterns, regardless of seasonal changes or soil moisture levels. This suggests these species are more drought-tolerant and could be a reliable choice for urban environments where water availability may fluctuate. The deciduous species (Ls), however, showed a marked decrease in water use and earlier stomatal closure—the closing of pores on the leaves—during dry conditions. While this helps the tree conserve water, it also suggests that Ls may require more irrigation during dry periods to thrive.

Greener Cities Ahead: Practical Implications for Urban Planners

By strategically selecting tree species based on their water use characteristics, cities can create more sustainable and resilient urban environments. Planting drought-tolerant species like Pterocarpus indicus and Swietenia macrophylla can reduce the demand for irrigation, conserving precious water resources. While Lagerstroemia speciosa may require more water during dry periods, its ability to conserve water through leaf shedding makes it a suitable choice for regions with distinct wet and dry seasons. Further research and field experiments are essential to validate these findings and tailor planting strategies to specific local conditions.

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Everything You Need To Know

Why is selecting the right tree species important for urban areas?

Selecting the right tree species is crucial for urban areas because it can significantly impact water consumption and sustainability. Different tree species have varying water needs and responses to drought conditions. By choosing species that require less water or are more drought-tolerant, cities can conserve water resources while still enjoying the benefits of urban forests. For instance, Pterocarpus indicus and Swietenia macrophylla are more drought-tolerant compared to Lagerstroemia speciosa.

What does the study in Bangkok reveal about different tree species and their water use?

The study in Bangkok examined the water use characteristics of three common tree species: Pterocarpus indicus, Swietenia macrophylla, and Lagerstroemia speciosa. It revealed that the semi-evergreen Pterocarpus indicus and evergreen Swietenia macrophylla exhibited more consistent water use patterns regardless of seasonal changes, suggesting higher drought tolerance. In contrast, the deciduous Lagerstroemia speciosa showed a marked decrease in water use during dry conditions, indicating it might require more irrigation during those times.

How do Pterocarpus indicus and Swietenia macrophylla compare in terms of water usage?

Both Pterocarpus indicus and Swietenia macrophylla exhibited more consistent water use patterns, regardless of seasonal changes or soil moisture levels. This indicates that both species are relatively drought-tolerant. Since Pterocarpus indicus is semi-evergreen and Swietenia macrophylla is evergreen, they both maintain their foliage for most of the year, requiring a steady water supply, but they manage water stress effectively, making them reliable choices for urban environments with fluctuating water availability.

What are the implications of Lagerstroemia speciosa reducing water use during dry conditions?

The fact that Lagerstroemia speciosa reduces water use and closes its stomata earlier during dry conditions is a survival mechanism. While this helps the tree conserve water, it also suggests that Lagerstroemia speciosa may require more irrigation during dry periods to thrive. This behavior makes it a suitable choice for regions with distinct wet and dry seasons, where its deciduous nature allows it to conserve water effectively during droughts but may need supplemental watering to maintain its aesthetic and ecological functions.

How can urban planners use the information about tree species and water consumption to create more sustainable cities?

Urban planners can use the information to strategically select tree species based on their water use characteristics. Planting drought-tolerant species like Pterocarpus indicus and Swietenia macrophylla can reduce the demand for irrigation, conserving water. For areas with distinct wet and dry seasons, Lagerstroemia speciosa may be suitable due to its ability to conserve water through leaf shedding, though supplemental irrigation might be needed. This approach optimizes water conservation and maximizes the ecological and aesthetic benefits of urban forests, making cities more sustainable and resilient.