by Femke van Woesik (MetaMeta), Lan Thanh Ha (Researcher, Institute of Water Resources Planning (IWRP), Ministry of Agriculture and Environment (MAE), Vietnam)
When discussing climate change, two approaches dominate the conversation: mitigation—reducing greenhouse gas emissions—and adaptation—adjusting to changing conditions. However, a third approach often goes unnoticed: managing local climates. By strategically altering landscapes to optimize water and vegetation cover, microclimate management can reduce temperatures and buffer against rising global temperatures. This localized intervention complements global mitigation and adaptation efforts, offering an additional solution to combat climate change effects.
Hydrological Ecosystem Services (HESS) and the Role of Water in Cooling
The cooling role of water is also represented in the Hydrological Ecosystem Services (HESS) framework by Ha et al. (2023), which describes the benefits of water beyond direct human use. HESS highlight how water contributes not only to food production and withdrawals but also to secondary benefits like water storage, purification, and temperature regulation. Despite their crucial role in ensuring environmental sustainability, climate adaptation, and human wellbeing, many HESS, including the cooling effects, are often overlooked. This is largely due to limited awareness and the absence of standardized frameworks for effective monitoring, assessment, and implementation.
How Local Cooling Works
Microclimate cooling is driven by the way solar energy interacts with landscapes. Incoming solar energy interacts with land surfaces and influences local temperature in two distinct pathways:
- Latent Heat Flux: Energy is used for evapotranspiration (water evaporation from soil and plant surfaces), which cools the air.
- Sensible Heat Flux: Energy heats the air and soil directly, raising temperatures.
The balance between these two processes depends on the landscape. In dry, barren areas with little vegetation and low soil moisture, most of the energy contributes to heating the air and soil. In contrast, lush landscapes with sufficient water promote evapotranspiration, diverting energy away from heating, thereby cooling the surrounding air. The key is to maximize latent heat flux while minimizing sensible heat flux, effectively reducing local temperatures, e.g., through reforestation, green-roof or wetland restoration etc.
The Cooling Effect of Vegetation and Water
Green spaces such as forests, wetlands, and irrigated fields thus act as natural air conditioners. Landscapes in the Netherlands (Figure 1) illustrate this phenomenon well. Measurements from fields with dense vegetation and moist soil recorded midday temperatures of 29.6°C, while fields with less vegetation reached 32.8°C—a 3.2°C cooling difference (Ha et al., 2023). Land surface temperatures can vary even more dramatically, underscoring the significant impact of vegetation and water in regulating climate.
In Vietnam, similar cooling effects have been observed. A study of the Day River Basin in Northern Vietnam found that well-vegetated areas provided a notable cooling effect, with an average temperature reduction of 2.7°C and a maximum cooling effect of 4.5–5°C in dense forests (Ha 2025, p. 88). Another example comes from the Kon-Ha Thanh and Tra Khuc Basins, which ranked among the highest for microclimate cooling benefits due to their landscape characteristics, vegetation cover, and water management practices (Ha 2025, p. 103). These cases demonstrate how hydrological ecosystem services play a vital role in cooling local climates.
Expanding Beyond Cooling: The Full Scope of HESS
Microclimate cooling is just one of 17 hydrological ecosystem services identified in the HESS framework. The framework also considers other crucial roles of water, such as sustaining local rainfall patterns. For example, HESS9 examines how land evapotranspiration influences long-term rainfall availability by recycling moisture back into the atmosphere. This process enhances precipitation levels and maintains water balance within river basins, reinforcing the interconnectedness of land, water, and climate.
For a deeper understanding of the full range of hydrological ecosystem services, including their impacts on water allocation policies and land-use planning, refer to the original research article by Ha et al. (2023). By integrating the HESS framework into decision-making, governments and agencies can better balance human water needs with environmental sustainability, ensuring a more climate-resilient future.
References
Ha, L. T., Bastiaanssen, W. G., Simons, G. W., & Poortinga, A. (2023). A New Framework of 17 Hydrological Ecosystem Services (HESS17) for Supporting River Basin Planning and Environmental Monitoring. Sustainability, 15(7), 6182. https://doi.org/10.3390/su15076182
Ha, L. T. (2025). Spatial mapping of hydrological ecosystem services for basin planning and natural capital accounting: Examples from Vietnam. Delft University of Technology. https://doi.org/10.4233/uuid:14083611-5177-47f3-919a-b23dd45c803f
Van Woesik, F., van Steenbergen, F., Sambalino, F., de Boer, H. J., Pace Ricci, J. M., & Bastiaanssen, W. (2023). Managing the local climate: A third way to respond to climate change. Practical Action Publishing.
