Kaleidoscope of Urban Evapotranspiration: Exploring the Science and Modeling Approaches

Urban evapotranspiration is a complex physical process. It depends on various critical drivers, including the land surface temperature (LST), surface albedo, landscape types, and building orientations. All of these factors create difficulties in the estimation of evapotranspiration (ET) by changing the microclimate conditions. The literature has oversimplified microclimate conditions by considering temperature difference as the only variable defining climate. The physical process depends on land-use changes, building proximities, and landscape types. This study devised three objectives to understand the microclimate effects on ET. In the first objective, land-use change effects on LST, surface albedo, and ET were analyzed over a period of twenty-seven years in the Las Vegas Valley. The analysis employed trends and shifts using Mann Kendal\u27s test and Pettit\u27s test, respectively. Land use encompassed four prominent urban surfaces, including residential, commercial, asphalt, and turf grass surfaces. The commercial and asphalt surfaces proved to be the main contributors to increased LST and decreased surface albedo. However, the increase in LST was lower than the rural surface increase, illustrating overall cooling in the summertime due to development. The removal of turf grass over the study period showed a significant increase in LST, while turf grass development showed an overall increase in ET. This study can help water managers and urban planners to understand the role of land-use change in irrigation water demand and urban thermal comfort. This study has been submitted to the Urban Climate Journal. The second objective was devised to understand the surface energy budget due to the presence and proximity of buildings. The study analyzed net radiation and soil heat flux, as well as the surface temperatures of canyons, rooftops, and turf grass, to understand day-time and nighttime warming. A 68 sq. km parcel in Phoenix, AZ was studied for the analysis. The findings suggest that canyons\u27 land surface temperatures (LST) were lower than rooftop surfaces, while turf grass surfaces were cooler than canyon surfaces. Moreover, north and south (N-S) oriented canyons were cooler than east and west (E-W) oriented canyons. No significant changes were observed in the net radiation for rooftop, turf grass, and canyon surfaces. However, the soil heat flux, warranting nighttime warming, showed higher absorption on rooftop surfaces than in canyons. The turf grass reported nighttime cooling, as the heat absorption was lower than the rooftop surfaces and the canyons. Additionally, a significant difference in heat absorption was observed between N-S oriented canyons and E-W oriented canyons. The study concluded that canyons and their orientations are major causes of daytime cooling and nighttime warming. For Phoenix, the N-S oriented streets are cooler than the E-W oriented streets. This study recommends studying canyons\u27 local municipalities, and developing a master plan for cities\u27 construction accordingly. This study has been submitted to the International Journal of Remote Sensing. The third objective investigated the microclimate effects and irrigation water requirements of three landscape types in an arid region of Phoenix, AZ. The microclimate effect encompassed surface temperature, air temperature, and wind speed. The three landscapes include mesic, oasis, and xeric. The simulation was conducted using ENVI-met software for the hottest day of the year (23rd June 2011). The simulated model was validated using ground data. The results showed that the mesic landscape induced cooling effects, both in the day-time and nighttime, by reducing the surface temperature, air temperature, and wind speed. However, the mesic landscape showed high-water consumption because of high leaf area density. The oasis landscape showed more day-time cooling than the mesic landscape, but the nighttime warming was like a xeric landscape. However, the potential irrigation water requirement was lower than the mesic landscape. Moreover, the surfaces between buildings showed varying microclimate conditions. In the case of mesic landscape, the surfaces showed high wind speeds and higher temperatures. The xeric landscape showed lower wind speeds and air temperatures between the buildings. Overall, the oasis landscape proved to be the most efficient of the three landscapes for water consumption and day-time cooling. This study will be submitted to the Journal of Advances in Modeling Earth Systems (JAMES), AGU. To sum up, both surface properties (land use) and orientation (canyons) affect the surface energy budget. Landscape type also contributes to air temperature and surface temperature changes, while air temperature changes related to wind speed. Changes in the surface energy budget affect ET rates in arid regions (Las Vegas Valley and Phoenix)

Greenery as a mitigation strategy to urban heat and air pollution: a comparative simulation-based study in a densely built environment.

The urban heat island and the urban air pollution concentration are two major climate-change-related phenomena affecting the built environment worldwide. This paper aims to verify the potential effect of different mitigation measures through a simulation study. In detail the present study focuses on the analysis of the environmental impacts of urban vegetation, such as green facades, vertical greenery, and green pavements. After an extensive screening of the literature review, an investigation of the impact of the most common built environment design variables in a defined case study led to the definition of a typical urban canyon was tested. The results show that the presence of trees in a street canyon could reduce the air temperature peaks by 5-10 °C, while the high-level vegetation canopies can lead to a deterioration in air quality with a PM concentration increasing by 1.2-1.5%. Instead, using low-level green infrastructure improves the air quality conditions on the sidewalk, reducing the NOx in the range of 10-20%. The analyzed high-level greenery generated an air temperature reduction effect on a street level ranging from 8 to 12°C. The present work contributes to clarifying the potential mitigation effect of green infrastructure in a densely built environment, where the risk of increasing temperatures and air pollutants is foreseen to be more intense in the coming years

Ecohydrology of Natural and Restored Wetlands in a Glacial Plain

More than half of wetland area in the U.S. have been converted to other land use types for agricultural use and development. Limited understanding of ecological services provided to society by wetlands is another reason for the massive wetland loss in the past. Section 404 of the Clean Water Act and the 1989 federal mandate of “no net wetland loss” supported increased efforts for wetland restoration and creation to compensate for two centuries of ecosystem degradation. Hydrology is a critical driver for wetland formation and sustainability, yet few studies have investigated the ecosystem benefits of restored or constructed wetlands relative to natural wetlands. Considering that unexpected ecohydrologic behaviors such as drought have been reported as a main cause of unsuccessful restoration over the U.S., understanding and quantifying water movement within the local seeing is imperative to future wetland restoration. From an environmental engineering perspective, wetlands are regarded as complex environments controlled by regional geomorphology, atmosphere, geologic setting, and human activity. The U.S. Army Corps of Engineers was tasked with developing a hydrogeomorphic assessment approach for wetlands in the various regions throughout the U.S. to facilitate wetland restoration. This effort was redirected in the aftermath of Hurricane Katrina, but the need for assessment tools persists for several remaining regions including the southern coastlines. The first part of the dissertation reports an investigation of impacts of geomorphic settings on hydrologic functions within the St. Lawrence River plain. Regional geomorphology links wetlands and surrounding areas by multiple pathways of water transfer such as groundwater exchange and surface water connections. However, recent U.S. Supreme Court rulings, including Solid Waste Agency of Northern Cook County versus U.S. Army Corps-SWANCC (2001) and Rapanos versus U.S. (2006) overturned federal protection of wetlands by the Clean Water Act unless the wetlands are shown to be geographically connected with jurisdictional waters. These rulings jeopardize mitigation wetlands without federal protection because typical restoration practices often minimize surface water connection as a result of dredge-and-fill methods. Hydrologic behaviors and services of the geographically isolated wetlands (GIWs) were hypothesized to be identical to those of geographically connected wetlands in this study. Experimental evidence suggest that hydrologic connectivity is maintained between GIWs and downstream waters via subsurface flow exchange. Greater correlations for GIWs than the other connectivity types were found between variables including standard deviation of groundwater, geographic attributes (e.g., site elevation) and hydrologic attributes (e.g., duration of subsurface flow reversal). Mean groundwater table depended most strongly on wetland fraction within a drainage area. Water temperature, particularly in summer, strongly influences the environmental suitability for wetland species such as a Blanding’s turtle (Emydoidea blandingii) for nesting in northern New York. Although temperature dependency of wetland fauna has been investigated to determine the range of suitable environmental conditions, the hydrogeomorphic controls on seasonal thermal regimes of wetlands were not addressed in prior studies. In this study, temperature regimes at multiple sites under uniform climate and geologic settings were investigated to understand the controls on wetland temperature in several of hydrogeomorphic settings. Local geomorphology and alterations by wetland restoration affected wetland thermal regimes via various seasonal subsurface flow exchange patterns. Thermal sensitivity is defined as a response in surface water temperature to change in air temperature. Based on wetland temperature measurements, linear regression was used to estimate thermal sensitivity for each site. Summer temperature values were shown as primary determinants by site comparison. In addition, the thermal sensitivity values were compared to site variables to seek for local controls. Results suggest that geographical and hydrologic variables including site elevation, duration of subsurface flow reversal, and standard deviation of wetland stage and groundwater table are significantly correlated with thermal sensitivity. Geomorphic settings are useful resources to characterize site hydrology and thermal functions of wetlands. Wetland restoration practitioners need to carefully choose class-appropriate hydrogeomorphic settings to promote establishment and conservation of temperature-sensitive species. Finally, the impact of the land surface energy budget was measured to assess the patch level controls on evapotranspiration by various wetland species. Infrared thermometry was used within a standard meteorological measurement system to determine energy partitioning between sensible and latent heat fluxes in wetlands. A portable thermal infrared (TIR) camera was used to capture radiometric surface temperature of leaves, i.e., evapotranspiring surfaces, and then to estimate sensible and thus latent heat flux associated with a portable weather station. Two TIR-based methods including TIR temperature-based surface energy balance (SEB) and Bowen ratio () were compared to the well-known Priestley-Taylor (P-T) method for four species-level patches. For wetland plants including hardstem bulrush (Scirpus Spp.), reed canary grass (Phalaris arundinacea), cattail (Typha Spp.) and meadow willow (Salix petiolaris), results are similar for the TIR-based and P-T methods with mean absolute difference of 17.1-53.0 W m-2 and root mean squared difference of 23.4-62.4 W m-2 across sites. Greater differences were found from parameterization of aerodynamic resistance for flexible and tall vegetation structure and especially for greater wind speed. Finally, estimated crop coefficients will be useful for regional wetland restoration planning by providing major losses in local water budget

Infrared radiative performance of urban trees: spatial distribution and interspecific comparison among ten species in the UK by in-situ spectroscopy

Understanding the ways in which tree species interact with solar radiation has previously focused on transmission and reflection of sunlight, typically by examining individual leaves. Here we used a tree crown spectroscopy measurement method to conduct in-situ tests on the radiative performance of ten commonly planted tree species in the UK. Tree crown transflectance (comprehensive effect of transmission and reflection) was examined to determine i), how radiative performance of individual trees varies spatially within a species, and ii), how infrared radiative performance differs between tree species. Our results show that tree crown transflectance depends on the combination of tree crown morphology, local foliage distribution (leaf density, gaps in crown foliage contour, concave or convex crown shapes), solar altitude and leaf size. Spatially, the strongest tree crown transflection was found primarily towards sky on the sunlit side of trees rather than towards the zenith, meaning that infrared transflection towards surrounding buildings and pedestrians is substantial. For all ten species, the tree crown transflectance in the frontal sunlit area was linearly correlated with solar altitude on sunny days. Hence, a solar altitude of 45° was chosen as the benchmark condition for comparing interspecific differences. Interspecific comparison indicated that interspecific differences in the infrared radiative performance levels were strongly dependent on leaf size when no obvious gaps or concave shapes were present within the tree crowns. Our findings provide insights for understanding radiative interactions between urban trees and surrounding built environment, as well as for tree species selection in urban heat stress mitigation

Progress in urban greenery mitigation science – assessment methodologies advanced technologies and impact on cities

Urban greenery is a natural solution to cool cities and provide comfort, clean air and significant social, health and economic benefits. This paper aims to present the latest progress on the field of greenery urban mitigation techniques including aspects related to the theoretical and experimental assessment of the greenery cooling potential, the impact on urban vegetation on energy, health and comfort and the acquired knowledge on the best integration of the various types of greenery in the urban frame. Also to present the recent knowledge on the impact of climate change on the cooling performance of urban vegetation and investigate and analyse possible technological solutions to face the impact of high ambient temperatures

Urban vegetation : towards cooler, biodiverse cities of the future

This thesis presents my doctoral research programme that aims to increase the understanding of the role that vegetation plays in functional urban ecosystems. To do this, I have systematically evaluated: (1) relationships between tree canopy traits and associated subcanopy cooling; (2) how planting context (e.g., parks or streets) influences the ability of trees to provide cooling benefits; (3) how canopy-associated cooling is influenced by ambient climatic conditions (solar radiation, vapor pressure deficit (VPD) and wind speed); and (4) how habitat/vegetation complexity influences invertebrate biodiversity, in urban settings across Greater Sydney. Whilst there has been some research exploring relationships between vegetation and landscape traits and urban temperature profiles, to date no study has systematically evaluated how different planting contexts, such as parks, nature strips or pavement/tarmac settings, influence the ability of trees to provide cooling benefits in the local environment. To address this gap, my research identifies those traits that determine the cooling potential of urban trees, alongside the impacts of planting context on the ability of trees to reduce air and surface temperatures. The first data chapter presents the results of a study across Greater Sydney that found tree shade reduced air and surface temperature by a maximum of 3.7 °C (mean 1.1 °C) and 45 °C (mean 27.4 °C), respectively. The magnitude and variability of tree-derived cooling benefits differ greatly among studies, likely reflecting differences in tree species’ traits, urban characteristics and local climate conditions. The second data chapter presents findings from a systematic study focused on ten commonly occurring species in western Sydney. In addition to the cooling benefits provided by trees, urban vegetation also provides other critical ecosystem services, including habitat and resources for a diverse range of vertebrate and invertebrate animal species. For example, an invertebrate-rich environment xi contributes to food security, nutrient cycling and pest control. Systematic explorations of the association between habitat/vegetation complexity and invertebrate biodiversity in urban areas are limited. My third data chapter therefore examined whether and how trees and shrubs differ in terms of the diversity, abundance and composition of associated invertebrate communities. Overall, my thesis research provides valuable new insights into the extent of cooling benefits provided by a variety of tree species in urban areas throughout Greater Sydney, and how these are influenced by tree canopy traits and local environmental conditions

Remote Sensing in Applications of Geoinformation

Remote sensing, especially from satellites, is a source of invaluable data which can be used to generate synoptic information for virtually all parts of the Earth, including the atmosphere, land, and ocean. In the last few decades, such data have evolved as a basis for accurate information about the Earth, leading to a wealth of geoscientific analysis focusing on diverse applications. Geoinformation systems based on remote sensing are increasingly becoming an integral part of the current information and communication society. The integration of remote sensing and geoinformation essentially involves combining data provided from both, in a consistent and sensible manner. This process has been accelerated by technologically advanced tools and methods for remote sensing data access and integration, paving the way for scientific advances in a broadening range of remote sensing exploitations in applications of geoinformation. This volume hosts original research focusing on the exploitation of remote sensing in applications of geoinformation. The emphasis is on a wide range of applications, such as the mapping of soil nutrients, detection of plastic litter in oceans, urban microclimate, seafloor morphology, urban forest ecosystems, real estate appraisal, inundation mapping, and solar potential analysis

The Spatial and Temporal Characteristics of the Urban Thermal Environment in East Africa: Implications for Sustainable Urban Development

Targeting cities in East Africa, where urbanisation and climate change are posing unprecedented threats to livelihoods and ecosystems, this thesis focuses on the combined effects of rapid urbanisation and climate change on Land Surface Temperature (LST), Surface Urban Heat Island (SUHI) effects and the role of Blue Green infrastructure (BGI) and vegetation dynamics. The aim of this thesis is to advance understanding of the urban thermal environment and the role of factors such as climate, vegetation and urbanisation patterns that add to its complexity. Through the use of satellite and remote sensing data (e.g., Google Earth Engine), spatial and statistical analyses, conducted in ArcGIS, Geoda and R, this thesis provides analyses of temporal trends between 2003 and 2017, and spatial differences in LST and SUHI in five East African cities (Khartoum, Addis Ababa, Kampala, Nairobi, Dar es Salaam). It advances understanding of how the configuration of urban areas affects the urban thermal environment, the amount of vegetation and surface water, and demonstrates the influence of urban density on the changes in SUHI intensity in both space and time. By linking the findings from the three results chapters and placing this in the context of the broader literature, corresponding policy implications and solutions are presented. The urgent need to provide a more detailed understanding of urban thermal environments, including macroclimate differences, seasonal variation and urban morphological characteristics, is highlighted. Recommendations emphasise the use of cloud-based analysis methods to overcome data scarcity, while the results point towards the utility of nature-based solutions for urban sustainable development. The methods and lessons emerging from this study can also be applied in other rapidly urbanising cities, where climate change is posing an unprecedented threat to livelihoods and ecosystems, and where resources are limited

The Built Environment in a Changing Climate

The papers included in this Special Issue tackle multiple aspects of how cities, districts, and buildings could evolve along with climate change and how this would impact our way of conceiving and applying design criteria, policies, and urban plans. Despite the multidisciplinary nature of the collection, some transversal take-home messages emerge: • Today’s energy-efficient paradigms may lose their virtuosity in the future unless accurate estimates of future scenarios are used to design modelling platforms and to inform legislative frameworks; • Acting at the local scale is key. Future climate change adaptation will be implemented at the local level. Overlooking regional and local specificities will contribute to inaccurate and inefficient action plans. As such, the smaller scale will become vital in predicting future urban metabolic rates and corresponding comfort-driven strategies; • Energy poverty, heat vulnerability, and social injustice are emerging as critical factors for planning and acting for future-proof cities on par of micro- and meso-climatological factors; • Given that the impacts of climate change will persist for many years, adaptation to this phenomenon should be prioritized by removing any prominent barrier and by enabling combinations of different mitigation technologies. These topics will receive a global reach in few decades, since also developing and underdeveloped countries are starting their fight against local climate change, with cities at the forefront