Local-Scale Urban Meteorological Parameterization Scheme Research Articles

Local-Scale Urban Energy Balance Observation under Various Sky Conditions in a Humid Subtropical Region

AbstractThe present study presents local-scale urban energy balance observations under various sky conditions in a humid subtropical region. The study site is a typical urban residential area in Guangzhou in which building density is 38%, vegetation coverage is 36%, and mean building height is 21 m. The observation was conducted at a 110-m-high tower using the eddy covariance technique from September to November 2016. The median diurnal pattern and daily maxima were achieved for all radiation components and turbulent fluxes. The Bowen ratio (β) results indicated a predominant role for sensible heat flux (QH) in the daytime and latent heat flux (QE) at night. The sky conditions played a significant part in the urban surface energy exchanges, showing that the median daily maxima of net radiation (Q*), QH, storage heat flux (ΔQS), surface albedo, and β all present a consistent order from large to small for clear, cloudy, and rainy days and a different order of rainy, clear, and cloudy days for QE. The mean daytime QH/Q*, QE/Q*, ΔQS/Q*, and β changed with urban density, while QE/Q* and β also varied with vegetation fraction. Furthermore, the adaptability of net all-wave radiation parameterization (NARP), objective hysteresis model (OHM), and local-scale urban meteorological parameterization scheme (LUMPS) were validated, given the index of agreements of 0.998 and 0.951 for Q* and ΔQS and the reasonable RMSEs for QH and QE. The present study helps to verify and improve the parameterizations of energy exchange over an urban surface in the humid subtropical region.

Energy flux parametrization as an opportunity to get Urban Heat Island insights: The case of Athens, Greece (Thermopolis 2009 Campaign)

Energy flux parameterization was effected for the city of Athens, Greece, by utilizing two approaches, the Local-Scale Urban Meteorological Parameterization Scheme (LUMPS) and the Bulk Approach (BA). In situ acquired data are used to validate the algorithms of these schemes and derive coefficients applicable to the study area. Model results from these corrected algorithms are compared with literature results for coefficients applicable to other cities and their varying construction materials. Asphalt and concrete surfaces, canyons and anthropogenic heat releases were found to be the key characteristics of the city center that sustain the elevated surface and air temperatures, under hot, sunny and dry weather, during the Mediterranean summer. A relationship between storage heat flux plus anthropogenic energy flux and temperatures (surface and lower atmosphere) is presented, that results in understanding of the interplay between temperatures, anthropogenic energy releases and the city characteristics under the Urban Heat Island conditions.

Tradeoffs Between Water Conservation and Temperature Amelioration In Phoenix and Portland: Implications For Urban Sustainability

This study addresses a classic sustainability challenge—the tradeoff between water conservation and temperature amelioration in rapidly growing cities, using Phoenix, Arizona and Portland, Oregon as case studies. An urban energy balance model— LUMPS (Local-Scale Urban Meteorological Parameterization Scheme)—is used to represent the tradeoff between outdoor water use and nighttime cooling during hot, dry summer months. Tradeoffs were characterized under three scenarios of land use change and three climate-change assumptions. Decreasing vegetation density reduced outdoor water use but sacrificed nighttime cooling. Increasing vegetated surfaces accelerated nighttime cooling, but increased outdoor water use by ~20%. Replacing impervious surfaces with buildings achieved similar improvements in nighttime cooling with minimal increases in outdoor water use; it was the most water-efficient cooling strategy. The fact that nighttime cooling rates and outdoor water use were more sensitive to land use scenarios than climate-change simulations suggested that cities can adapt to a warmer climate by manipulating land use.

Flux Measurements in Cairo. Part 2: On the Determination of the Spatial Radiation and Energy Balance Using ASTER Satellite Data

This study highlights the possibilities and constraints of determining instantaneous spatial surface radiation and land heat fluxes from satellite images in a heterogeneous urban area and its agricultural and natural surroundings. Net radiation was determined using ASTER satellite data and MODTRAN radiative transfer calculations. The soil heat flux was estimated with two empirical methods using radiative terms and vegetation indices. The turbulent heat fluxes finally were determined with the LUMPS (Local-Scale Urban Meteorological Parameterization Scheme) and the ARM (Aerodynamic Resistance Method) method. Results were compared to in situ measured ground data. The performance of the atmospheric correction was found to be crucial for the estimation of the radiation balance and thereafter the heat fluxes. The soil heat flux could be modeled satisfactorily by both of the applied approaches. The LUMPS method, for the turbulent fluxes, appeals by its simplicity. However, a correct spatial estimation of associated parameters could not always be achieved. The ARM method showed the better spatial results for the turbulent heat fluxes. In comparison with the in situ measurements however, the LUMPS approach rendered the better results than the ARM method.

Land Cover Modification Scenarios and Their Effects on Daytime Heating in the Inner Core Residential Neighborhoods of Phoenix, Arizona

This study addresses simulations of summertime atmospheric heating/cooling and water use at the local scale in Phoenix, Arizona—a city in the arid Southwestern United States. Our goal is to consider various climate effects by the manipulation of land cover within census tracts at the local scale. This scale refers to horizontal areas of approximately 102–104 m on a side and to measurement heights in the inertial sublayer above the urban canopy and its roughness sublayer. The model we use for this scale is the Local Scale Urban Meteorological Parameterization Scheme (LUMPS) after Grimmond and Oke (2002). We calculate different scenarios using the LUMPS model to determine the interplay of water use and summer diurnal variations of atmospheric heating and cooling processes for selected census tracts in Phoenix. First, we simulate xeriscaping within the census tract neighborhoods by transforming green spaces into soil. The second scenario simulates an infill and Brownfield development scenario, increasing density and impervious surfaces while at the same time decreasing soil. Third, we reduce barren soil and impervious surface areas to simulate a green city. With LUMPS we can understand the optimization of water use and at the same time the maximization of the cooling potential within the local scale area as a whole, dependent on varying the total surface cover fractions. In urban planning, LUMPS can be used as a scenario-based tool to design pedestrian-friendly sustainable development in desert climates where land cover is tailored to reduce UHI effects and to induce more comfortable daytime temperatures.

Land cover, climate, and the summer surface energy balance in Phoenix, AZ, and Portland, OR

AbstractChanges in land use and land cover alter the local energy balance and contribute to distinct urban climates. This paper presents a local‐scale above‐canopy study of intra‐urban land cover mixes in two cities to analyse the relative effects of surface morphology and local climate on the surface energy balance (SEB). The study is conducted for urban areas in Phoenix, Arizona, and Portland, Oregon, cities with distinct climates but similarly warm and dry summers. A Local‐Scale Urban Meteorological Parameterization Scheme (LUMPS) is used to analyse the relative contributions of local weather extremes and land cover variations on the urban energy balance. The partitioning of net all‐wave radiation into turbulent sensible and latent heat fluxes as well as heat storage is investigated for a typical dry summer month and two extreme weather scenarios in the two cities. Results of sensitivity analyses show that incoming solar radiation is an important driver of the SEB in LUMPS and should be considered in the generation of climate scenarios. The relationship between individual land cover fractions and SEB fluxes is not clear because of interrelated effects of surface characteristics in the land cover mix. Daytime Bowen ratios vary inversely with vegetation fraction between and within cities for all weather scenarios. Impervious surface cover is positively correlated to the available energy that is partitioned into sensible heat. Cumulative evapotranspiration (ET) is similar for average weather conditions across medium wet sites in Phoenix and Portland but varies more in Portland than in Phoenix under extreme weather conditions. Results suggest that land cover manipulation could offset influences of weather extremes on ET in Portland to a certain degree but not in Phoenix. These findings highlight the importance of spatial and climatic context in the urban design process to mitigate the effects of urbanization. Copyright © 2011 Royal Meteorological Society

Modeling the impact of land use and climate change on neighborhood-scale evaporation and nighttime cooling: A surface energy balance approach

We investigated the impacts of temperature changes derived from climate change scenarios and land cover change on patterns of external residential water consumption and nighttime cooling in suburban Hillsboro, Oregon. Three downscaled climate warming scenarios and two land cover change scenarios (sprawl and dense) for the 2040s were used as inputs for an urban energy balance model, the Local-Scale Urban Meteorological Parameterization Scheme (LUMPS). Based on the surface energy fluxes simulated by the LUMPS model, we calculate that the combination of the sprawl scenario with the 3 °C temperature rise increases external water consumption by 4061 L per household for August. Alternately, dense development concomitant with temperature increase constrains increases in water consumption, but reduces nighttime cooling rates by more than 0.3 °C. Increasing the fraction of trees would increase efficiency in promoting urban cooling while reducing external water consumption. This study demonstrates that urban land cover and water use are naturally intertwined at the neighborhood scale, suggesting that urban land-use planning and water management should be fully integrated to design cities that can accommodate future population growth and development while minimizing negative impacts of potential climate change.

Local-Scale Urban Meteorological Parameterization Scheme (LUMPS): Longwave Radiation Parameterization and Seasonality-Related Developments

Abstract Recent developments to the Local-scale Urban Meteorological Parameterization Scheme (LUMPS), a simple model able to simulate the urban energy balance, are presented. The major development is the coupling of LUMPS to the Net All-Wave Radiation Parameterization (NARP). Other enhancements include that the model now accounts for the changing availability of water at the surface, seasonal variations of active vegetation, and the anthropogenic heat flux, while maintaining the need for only commonly available meteorological observations and basic surface characteristics. The incoming component of the longwave radiation (L↓) in NARP is improved through a simple relation derived using cloud cover observations from a ceilometer collected in central London, England. The new L↓ formulation is evaluated with two independent multiyear datasets (Łódź, Poland, and Baltimore, Maryland) and compared with alternatives that include the original NARP and a simpler one using the National Climatic Data Center cloud observation database as input. The performance for the surface energy balance fluxes is assessed using a 2-yr dataset (Łódź). Results have an overall RMSE < 34 W m−2 for all surface energy balance fluxes over the 2-yr period when using L↓ as forcing, and RMSE < 43 W m−2 for all seasons in 2002 with all other options implemented to model L↓.

Using Watered Landscapes to Manipulate Urban Heat Island Effects: How Much Water Will It Take to Cool Phoenix?

Problem: The prospect that urban heat island (UHI) effects and climate change may increase urban temperatures is a problem for cities that actively promote urban redevelopment and higher densities. One possible UHI mitigation strategy is to plant more trees and other irrigated vegetation to prevent daytime heat storage and facilitate nighttime cooling, but this requires water resources that are limited in a desert city like Phoenix. Purpose: We investigated the tradeoffs between water use and nighttime cooling inherent in urban form and land use choices. Methods: We used a Local-Scale Urban Meteorological Parameterization Scheme (LUMPS) model to examine the variation in temperature and evaporation in 10 census tracts in Phoenix's urban core. After validating results with estimates of outdoor water use based on tract-level city water records and satellite imagery, we used the model to simulate the temperature and water use consequences of implementing three different scenarios. Results and conclusions: We found that increasing irrigated landscaping lowers nighttime temperatures, but this relationship is not linear; the greatest reductions occur in the least vegetated neighborhoods. A ratio of the change in water use to temperature impact reached a threshold beyond which increased outdoor water use did little to ameliorate UHI effects. Takeaway for practice: There is no one design and landscape plan capable of addressing increasing UHI and climate effects everywhere. Any one strategy will have inconsistent results if applied across all urban landscape features and may lead to an inefficient allocation of scarce water resources. Research Support: This work was supported by the National Science Foundation (NSF) under Grant SES-0345945 (Decision Center for a Desert City) and by the City of Phoenix Water Services Department. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of NSF.

Modelling of urban sensible heat flux at multiple spatial scales: A demonstration using airborne hyperspectral imagery of Shanghai and a temperature–emissivity separation approach

Urbanization related alterations to the surface energy balance impact urban warming (‘heat islands’), the growth of the boundary layer, and many other biophysical processes. Traditionally, in situ heat flux measures have been used to quantify such processes, but these typically represent only a small local-scale area within the heterogeneous urban environment. For this reason, remote sensing approaches are very attractive for elucidating more spatially representative information. Here we use hyperspectral imagery from a new airborne sensor, the Operative Modular Imaging Spectrometer (OMIS), along with a survey map and meteorological data, to derive the land cover information and surface parameters required to map spatial variations in turbulent sensible heat flux ( Q H). The results from two spatially-explicit flux retrieval methods which use contrasting approaches and, to a large degree, different input data are compared for a central urban area of Shanghai, China: (1) the Local-scale Urban Meteorological Parameterization Scheme (LUMPS) and (2) an Aerodynamic Resistance Method (ARM). Sensible heat fluxes are determined at the full 6 m spatial resolution of the OMIS sensor, and at lower resolutions via pixel aggregation and spatial averaging. At the 6 m spatial resolution, the sensible heat flux of rooftop dominated pixels exceeds that of roads, water and vegetated areas, with values peaking at ∼ 350 W m − 2 , whilst the storage heat flux is greatest for road dominated pixels (peaking at around 420 W m − 2 ). We investigate the use of both OMIS-derived land surface temperatures made using a Temperature–Emissivity Separation (TES) approach, and land surface temperatures estimated from air temperature measures. Sensible heat flux differences from the two approaches over the entire 2 × 2 km study area are less than 30 W m − 2 , suggesting that methods employing either strategy maybe practica1 when operated using low spatial resolution (e.g. 1 km) data. Due to the differing methodologies, direct comparisons between results obtained with the LUMPS and ARM methods are most sensibly made at reduced spatial scales. At 30 m spatial resolution, both approaches produce similar results, with the smallest difference being less than 15 W m − 2 in mean Q H averaged over the entire study area. This is encouraging given the differing architecture and data requirements of the LUMPS and ARM methods. Furthermore, in terms of mean study Q H, the results obtained by averaging the original 6 m spatial resolution LUMPS-derived Q H values to 30 and 90 m spatial resolution are within ∼ 5 W m − 2 of those derived from averaging the original surface parameter maps prior to input into LUMPS, suggesting that that use of much lower spatial resolution spaceborne imagery data, for example from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) is likely to be a practical solution for heat flux determination in urban areas.

Turbulent Heat Fluxes in Urban Areas: Observations and a Local-Scale Urban Meteorological Parameterization Scheme (LUMPS)

Abstract A linked set of simple equations specifically designed to calculate heat fluxes for the urban environment is presented. This local-scale urban meteorological parameterization scheme (LUMPS), which has similarities to the hybrid plume dispersion model (HPDM) scheme, requires only standard meteorological observations and basic knowledge of surface cover. LUMPS is driven by net all-wave radiation. Heat storage by the urban fabric is parameterized from net all-wave radiation and surface cover information using the objective hysteresis model (OHM). The turbulent sensible and latent heat fluxes are calculated using the available energy and are partitioned using the approach of de Bruin and Holtslag, and Holtslag and van Ulden. A new scheme to define the Holtslag and van Ulden α and β parameters for urban environments is presented; α is empirically related to the plan fraction of the surface that is vegetated or irrigated, and a new urban value of β captures the observed delay in reversal of the sign of...