Naika Meili

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Meili

First Name

Naika

ORCID

0000-0001-6283-2134

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Publications 1 - 10 of 17

Influence of urban form and function on daytime-nighttime population differences and hazard risk assessments
Zhu, Yue; Wang, Jing; Manoli, Gabriele; et al. (2025)
npj Urban Sustainability
Neglecting the temporal variations in population distribution can lead to significant discrepancies in exposure estimations for disaster management, especially in the face of increasing natural hazards due to climate change. Effective disaster management necessitates a nuanced understanding of how the urban environment influences the temporal variations in population distribution. This study addresses this knowledge gap by investigating the relationship between the spatial patterns of urban elements and daytime-nighttime population differences across eight European cities. The study reveals a substantial association between urban form indicators and daytime-nighttime population differences. Although the findings suggest that there is no one-size-fits-all set of indicators for different cities, ‘closeness centrality’, which measures the accessibility of a specific location within the overall street network, is identified as a key proxy for daytime-nighttime population differences across all cities analysed, which can be further linked to the accuracy of hazard exposure estimation. These findings can contribute to enhancing urban resilience by offering insights into spatio-temporal population dynamics and considering their implications for disaster management.
Effects of green spaces on urban climate and hydrology from global to local scales
Manoli, Gabriele; Meili, Naika; Bou-Zeid, Elie; et al. (2019)
AGU Fall Meeting Abstracts
An urban ecohydrological model to quantify the effect of vegetation on urban climate and hydrology (UT&C v1.0)
Meili, Naika; Manoli, Gabriele; Burlando, Paolo; et al. (2020)
Geoscientific Model Development
Increasing urbanization is likely to intensify the urban heat island effect, decrease outdoor thermal comfort, and enhance runoff generation in cities. Urban green spaces are often proposed as a mitigation strategy to counteract these adverse effects, and many recent developments of urban climate models focus on the inclusion of green and blue infrastructure to inform urban planning. However, many models still lack the ability to account for different plant types and oversimplify the interactions between the built environment, vegetation, and hydrology. In this study, we present an urban ecohydrological model, Urban Tethys-Chloris (UT&C), that combines principles of ecosystem modelling with an urban canopy scheme accounting for the biophysical and ecophysiological characteristics of roof vegetation, ground vegetation, and urban trees. UT&C is a fully coupled energy and water balance model that calculates 2 m air temperature, 2 m humidity, and surface temperatures based on the infinite urban canyon approach. It further calculates the urban hydrological fluxes in the absence of snow, including transpiration as a function of plant photosynthesis. Hence, UT&C accounts for the effects of different plant types on the urban climate and hydrology, as well as the effects of the urban environment on plant well-being and performance. UT&C performs well when compared against energy flux measurements of eddy-covariance towers located in three cities in different climates (Singapore, Melbourne, and Phoenix). A sensitivity analysis, performed as a proof of concept for the city of Singapore, shows a mean decrease in 2 m air temperature of 1.1 ∘C for fully grass-covered ground, 0.2 ∘C for high values of leaf area index (LAI), and 0.3 ∘C for high values of Vc,max (an expression of photosynthetic capacity). These reductions in temperature were combined with a simultaneous increase in relative humidity by 6.5 %, 2.1 %, and 1.6 %, for fully grass-covered ground, high values of LAI, and high values of Vc,max, respectively. Furthermore, the increase of pervious vegetated ground is able to significantly reduce surface runoff.
Detailed investigation of vegetation effects on microclimate by means of computational fluid dynamics (CFD) in a tropical urban environment
Mughal, Muhammad Omer; Kubilay, Aytaç; Fatichi, Simone; et al. (2021)
Urban Climate
In light of globally increasing temperatures, accentuated in cities by the urban heat island effect, urban planners and designers are looking for new, quantitative methods to assess the performance of their designs in terms of ecosystem services provided by vegetation. Among these ecosystem services, improved microclimate conditions are particularly important for human thermal comfort and health. In this study, an urban scene in the tropical city of Singapore is numerically investigated with a fully-integrated, three-dimensional urban microclimate model implemented in OpenFOAM. Mass and heat transport in air and storage effect in the urban environment are coupled so that the daily turbulent transport in air using steady Reynolds-averaged Navier-Stokes (RANS) can be solved iteratively with the unsteady heat and moisture transfer from urban surfaces. Vegetation is modeled as a porous medium for the flow of moist air and a leaf energy balance model is used to determine the heat fluxes and transpiration at leaf surfaces. The analysis shows the influence of an urban park upon air temperatures and thermal comfort. Cooling intensity of 1 °C is observed downwind of the park within a region of 27 m for an incoming wind speed of 2.3 m s−1, which reduces to 0.6 °C at a distance of 117 m from the park. The Universal Thermal Comfort Index (UTCI) shows a reduction in thermal stress in and around the park. The approach presented here can provide specific guidelines for urban planners and frame expectations on magnitude and spatial extent of local microclimate modifications generated by an urban park in a tropical city.
Urban Forests as Main Regulator of the Evaporative Cooling Effect in Cities
Paschalis, Athanasios; Chakraborty, TC; Fatichi, Simone; et al. (2021)
AGU Advances
Higher temperatures in urban areas expose a large fraction of the human population to potentially dangerous heat stress. Green spaces are promoted worldwide as local and city-scale cooling strategies but the amount, type, and functioning of vegetation in cities lack quantification and their interaction with urban climate in different settings remains a matter of debate. Here we use state-of-the-art remote sensing data from 145 city clusters to disentangle the drivers of surface urban heat islands (SUHI) intensity and quantify urban-rural differences in vegetation cover, species composition, and evaporative cooling. We show that nighttime SUHIs are affected mostly by abiotic factors, while daytime SUHIs are highly correlated with vegetation characteristics and the wetness of the background climate. Magnitude and seasonality of daytime SUHIs are controlled by urban-rural differences in plant transpiration and leaf area, which explain the dependence of SUHIs on wetness conditions. Leaf area differences are caused primarily by changes in vegetation type and a loss of in-city forested areas, highlighting the importance of maintaining "natural reserves" as a sustainable heat mitigation policy.
Aerodynamic effects cause higher forest evapotranspiration and water yield reductions after wildfires in tall forests
Meili, Naika; Beringer, Jason; Zhao, Jiacheng; et al. (2024)
Global Change Biology
Wildfires are increasing in frequency, intensity, and extent globally due to climate change and they can alter forest composition, structure, and function. The destruction and subsequent regrowth of young vegetation can modify the ecosystem evapotranspiration and downstream water availability. However, the response of forest recovery on hydrology is not well known with even the sign of evapotranspiration and water yield changes following forest fires being uncertain across the globe. Here, we quantify the effects of forest regrowth after catastrophic wildfires on evapotranspiration and runoff in the world's tallest angiosperm forest (Eucalyptus regnans) in Australia. We combine eddy covariance measurements including pre- and post-fire periods, mechanistic ecohydrological modeling and then extend the analysis spatially to multiple fires in eucalypt-dominated forests in south-eastern Australia by utilizing remote sensing. We find a fast recovery of evapotranspiration which reaches and exceeds pre-fire values within 2 years after the bushfire, a result confirmed by eddy covariance data, remote sensing, and modeling. Such a fast evapotranspiration recovery is likely generalizable to tall eucalypt forests in south-eastern Australia as shown by remote sensing. Once climate variability is discounted, ecohydrological modeling shows evapotranspiration rates from the recovering forest which reach peak values of +20% evapotranspiration 3 years post-fire. As a result, modeled runoff decreases substantially. Contrary to previous research, we find that the increase in modeled evapotranspiration is largely caused by the aerodynamic effects of a much shorter forest height leading to higher surface temperature, higher humidity gradients and therefore increased transpiration. However, increases in evapotranspiration as well as decreases in runoff caused by the young forest are constrained by energy and water limitations. Our result of an increase in evapotranspiration due to aerodynamic warming in a shorter forest after wildfires could occur in many parts of the world experiencing forest disturbances.
Residential tree canopy configuration and mortality in 6 million Swiss adults: a longitudinal study
Chi, Dengkai; Manoli, Gabriele; Lin, Brenda; et al. (2025)
The Lancet Planetary Health
Background: Residential exposure to trees has been associated with reduced mortality risks. We hypothesise that in addition to tree canopy cover, tree canopy configuration also plays a role in exposure-mortality relationships. As there is limited evidence on this hypothesis, especially longitudinal evidence, we performed a nationwide study to investigate the residential tree canopy configuration-mortality associations in the Swiss population. Methods: In this longitudinal study, the tree canopy cover and configuration metrics within 500 m of individuals' residences were quantified using high-resolution tree canopy data (1 x 1 m) from 2010 to 2019. We developed single-exposure and multi-exposure time-varying Cox regression models to estimate the associations between the different exposure metrics and natural-cause and cause-specific mortality in Swiss adults (aged from 20 years to 90 years). Mortality and census data were taken from the Swiss National Cohort (SNC). We estimated the hazard ratios (HRs) and corresponding 95% CIs per IQR increase in the metrics adjusting for personal sociodemographic and contextual covariates. We also explored the effect modification by tree canopy cover, PM$_{10}$, air temperature, urbanisation level, age, sex, and area-based local socioeconomic position. Findings: Our analyses included 6 215 073 individuals from the SNC between 2010 and 2019. In the fully adjusted single-exposure models, we observed protective associations between natural-cause mortality risk and tree canopy cover (IQR 12$\cdot$4%, 0$\cdot$979 [95% CI 0$\cdot$975 - 0$\cdot$983]) and configuration metrics describing the aggregation (6$\cdot$3%, 0$\cdot$831 [0$\cdot$823 - 0$\cdot$840]), and connectedness (2$\cdot$9%, 0$\cdot$946 [0$\cdot$938 - 0$\cdot$953]); and detrimental associations with two metrics describing the fragmentation (211 patches per 100 ha, 1$\cdot$073 [1$\cdot$066 - 1$\cdot$080]) and shape complexity (1$\cdot$9, 1$\cdot$094 [1$\cdot$089 - 1$\cdot$100]) of patches. The associations were generally preserved with other common causes of death. According to the multi-exposure models, the HR (95% CI) for the combination of one IQR decrease in aggregation and one IQR increase in fragmentation and shape complexity was 1$\cdot$366 (1$\cdot$343 - 1$\cdot$390). Analyses on modification effects suggested a stronger association in people living in areas with a higher level of tree canopy cover, PM$_{10}$ concentration, air temperature, and urbanisation level. Interpretation: Aggregated, connected, and less fragmented forested greenspaces might offer stronger health benefits than isolated, fragmented ones, but are difficult to implement in cities. Our study provided valuable insights into optimising forested greenspaces and highlighted future directions for the planning and management of urban forests towards healthy and green cities.
Tree effects on urban microclimate: diurnal, seasonal, and climatic temperature differences explained by separating radiation, evapotranspiration, and roughness effects
Meili, Naika; Manoli, Gabriele; Burlando, Paolo; et al. (2021)
Urban Forestry & Urban Greening
Increasing urban tree cover is an often proposed mitigation strategy against urban heat as trees are expected to cool cities through evapotranspiration and shade provision. However, trees also modify wind flow and urban aerodynamic roughness, which can potentially limit heat dissipation. Existing studies show a varying cooling potential of urban trees in different climates and times of the day. These differences are so far not systematically explained as partitioning the individual tree effects is challenging and impossible through observations alone. Here, we conduct numerical experiments removing and adding radiation, evapotranspiration, and aerodynamic roughness effects caused by urban trees using a mechanistic urban ecohydrological model. Simulations are presented for four cities in different climates (Phoenix, Singapore, Melbourne, Zurich) considering the seasonal and diurnal cycles of air and surface temperatures. Results show that evapotranspiration of well-watered trees alone can decrease local 2 m air temperature at maximum by 3.1 – 5.8 °C in the four climates during summer. Further cooling is prevented by stomatal closure at peak temperatures as high vapour pressure deficits limit transpiration. While shading reduces surface temperatures, the interaction of a non-transpiring tree with radiation can increase 2 m air temperature by up to 1.6 – 2.1 °C in certain hours of the day at local scale, thus partially counteracting the evapotranspirative cooling effect. Furthermore, in the analysed scenarios, which do not account for tree wind blockage effects, trees lead to a decrease in urban roughness, which inhibits turbulent energy exchange and increases air temperature during daytime. At night, single tree effects are variable likely due to differences in atmospheric stability within the urban canyon. These results explain reported diurnal, seasonal and climatic differences in the cooling effects of urban trees, and can guide future field campaigns, planning strategies, and species selection aimed at improving local microclimate using urban greenery.
Modeling the Effect of Trees on Energy Demand for Indoor Cooling and Dehumidification Across Cities and Climates
Meili, Naika; Zheng, Xing; Takane, Yuya; et al. (2025)
Journal of Advances in Modeling Earth Systems
Increasing urban tree cover is a common strategy to lower urban temperatures and indirectly the building energy demand for air-conditioning (AC). However, urban vegetation leads to increasing humidity with potential negative effects on the AC dehumidification loads in hot-humid climates, an effect that has so far been unexplored. Here, we included a building energy model into the urban ecohydrological model Urban Tethys-Chloris (UT&C-BEM) to quantify the AC energy reduction effects of trees in seven hot cities with varying background humidity. A numerical experiment was performed simulating various urban densities and tree cover scenarios in the city-climates of Riyadh, Phoenix, Dubai, New Delhi, Singapore, Lagos, and Tokyo. The relative contribution of tree shade, air temperature reduction, and humidity increase on the AC energy reduction was further quantified. We found that well-watered trees provide the largest average summer AC energy reduction of -17% in the hot-dry climate (Riyadh, Phoenix). As tree shade is the dominant factor leading to the AC energy reduction in all city-climates, humid cities also show an average summer AC energy reduction ranging from -6% to -9%. However, increasing humidity is affecting AC dehumidification loads, especially under higher ventilation rates in humid climates and in these cities, AC energy reduction is most efficient with up to 40% tree cover. Additionally, we found that trees effectively reduce peak AC energy consumption due to higher shading effects in those hours. These results can inform urban planning strategies to maximize reduction in the AC energy demand using urban trees. Plain Language Summary Urban trees can provide multiple benefits, such as reducing temperature and potentially air-conditioning (AC) energy consumption, but they might increase humidity. During AC operation, air is not only cooled but also dehumidified, which requires energy, to prevent indoor mold formation and health problems. However, a quantification of the humidity effects of urban trees on the AC energy consumption in hot-humid cities has so far been lacking. Here, we quantify how urban trees influence the summer AC energy consumption in different climates (Riyadh, Phoenix, Dubai, New Delhi, Singapore, Lagos, and Tokyo). We found that well-watered trees lead to the largest average AC energy reduction of -17% in hot-dry cities. In all cities, tree shading is the dominant factor leading to reduced AC energy consumption. Because of this, we also simulated an average AC energy reduction in hot-humid cities of -6% to -9%. However, increasing humidity leads to raised energy consumption for dehumidification, especially when indoor-outdoor air exchange is high. In hot-humid cities, AC energy reduction due to trees is the most efficient with up to 40% tree cover. Trees also provide larger energy reduction during AC peak hours. These findings can inform urban planning strategies to maximize the ecosystem services provided by trees.
Vegetation Biophysical and Ecophysiological Properties Mediating Urban Microclimate and Water Fluxes: A Modelling Study
Meili, Naika; Fatichi, Simone; Manoli, Gabriele; et al. (2019)
16th Annual Meeting AOGS, Abstracts

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