scholarly journals Seasonal variation of dry and wet islands in Beijing considering urban artificial water dissipation

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Zhuoran Luo ◽  
Jiahong Liu ◽  
Yongxiang Zhang ◽  
Jinjun Zhou ◽  
Weiwei Shao ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Relative Humidity ◽  
Urban Areas ◽  
Urban Canopy ◽  
Absolute Humidity ◽  
Weather Research And Forecasting ◽  
Island Effect ◽  
Typical Summer ◽  
Canopy Model ◽  
Artificial Water

AbstractUrbanization has resulted in dry/wet island effects in built-up areas. Compared to the limited number of observational datasets, simulations can provide data with richer spatial distribution, thereby proving to be more helpful for revealing the spatial distribution of dry/wet islands. This study simulated dry/wet island effects during typical summer and winter conditions in Beijing by coupling the Artificial Water Dissipation Urban Canopy Model with the Weather Research and Forecasting model. Observations of relative humidity, absolute humidity, and temperature from weather stations in Beijing were used to verify the model. The results showed that in 2020, Beijing was prone to be a dry island during summer, with the relative humidity approximately 5–10% lower than the surrounding suburbs. The dry island effect was not obvious in winter, and Beijing tended to be a wet island. The influence of artificial water dissipation on dry/wet islands is higher in winter than in summer. By considering the water vapor from artificial water dissipation, humidity in urban areas can be simulated more accurately.

scholarly journals Temporal–Spatial Patterns of Relative Humidity and the Urban Dryness Island Effect in Beijing City

2017 ◽  
Vol 56 (8) ◽  
pp. 2221-2237 ◽  
Author(s):  
Ping Yang ◽  
Guoyu Ren ◽  
Wei Hou
Keyword(s):  
Relative Humidity ◽  
Urban Areas ◽  
Late Summer ◽  
Beijing City ◽  
Near Surface ◽  
Suburban Areas ◽  
Island Effect ◽  
Different Seasons ◽  
Autumn And Winter ◽  
Beijing China

AbstractHourly datasets obtained by automatic weather stations in Beijing, China, are developed and employed to analyze the spatial and temporal characteristics of relative humidity (RH) and urban dryness island intensity (UDII) over built-up areas. A total of 36 stations inside the sixth ring road are considered as urban sites, while six stations in suburban belts surrounding the built-up areas are taken as reference sites. Results show that the RH is obviously smaller in urban areas than in suburban areas, indicating the effect of urbanization on near-surface atmospheric moisture and RH. A further analysis of relations between RH and temperature on varied time scales shows that the variations in RH in the urban areas are not due solely to changes in temperature. The annual and seasonal mean UDII are high in central urban areas, with the strongest UDII values occurring in autumn and the weakest values occurring in spring. The diurnal UDII variations are characterized by a steadily strong UDII stage from 2000 to 0800 LT and a minimum at 1500 or 1600 LT. The rapid shifts of UDII from high (low) to low (high) occur during the periods 0800–1600 LT (1600–2000 LT). The occurrence time of the peaks varies among different seasons: the peaks appear at 0700, 2100, 2000, and 0800 LT for spring, summer, autumn, and winter, respectively. Further analysis shows that large UDII values appear in the evenings and early nights in late summer and early to midautumn and that low UDII values mainly occur in the afternoon hours of spring, winter, and late autumn.

scholarly journals Absolute moisture content in mid-latitude urban canopy layer

2018 ◽  
Vol 51-52 (1) ◽  
pp. 37-45 ◽  
Author(s):  
János Unger ◽  
Nóra Skarbit ◽  
Tamás Gál
Keyword(s):  
Spatial Distribution ◽  
Moisture Content ◽  
Case Studies ◽  
Urban Canopy ◽  
Absolute Humidity ◽  
Temperature Dependent ◽  
Canopy Layer ◽  
Urban Canopy Layer ◽  
Absolute Measure ◽  
Urban Rural

This part of the study on absolute moisture content in the mid-latitude urban canopy layer first gives a comparison on intra-urban relative and absolute humidity patterns showing an example based on a long dataset. The comparison clearly demonstrates the usefulness of the utilization of absolute measure opposite to the temperature dependent relative one. This supports the earlier statements found in the literature albeit these statements are based on only case studies or short datasets. Then a short overview follows which presents the main results of studies about urban absolute moisture content. These studies focused mainly on urban-rural and less on intra-urban humidity differences. The scale differences are used for the grouping of studies based on the number of available measurement sites as well as their spatial distribution and density in the investigated urban regions.

scholarly journals The Influences of Urban Building Complexes on the Ambient Flows over the Washington–Reston Region

2019 ◽  
Vol 58 (6) ◽  
pp. 1325-1336 ◽  
Author(s):  
Da-Lin Zhang ◽  
Menglin S. Jin ◽  
Yixuan Shou ◽  
Chunqing Dong
Keyword(s):  
Mesoscale Model ◽  
Urban Canopy ◽  
Static Stability ◽  
Wake Flow ◽  
Weather Research And Forecasting ◽  
Flow Strength ◽  
Blocking Effects ◽  
Downwind Side ◽  
Urban Heat ◽  
Canopy Model

AbstractThis paper examines the collective impacts of urban building complexes on the planetary boundary layer (PBL) winds using both observations and a mesoscale model. Horizontal winds measured on the rooftops of federal buildings over the regions of Washington, D.C., and a small city nearby (i.e., Reston, Virginia) show the blocking effects of urban building complexes on the downstream winds during the daytime of 9 July 2007. A modeling study of the case using a coupled version of the Weather Research and Forecasting (WRF)–multilayer urban canopy model in which the observed building height and density information is implemented to advance the calculations of momentum and heat, reproduces the rooftop-observed wind patterns and the related urban heat island effects, especially the wake flows on the downstream sides of the above-mentioned two cities. Results show that under daytime conditions the building complexes can collectively form a mesoscale wake on the downwind side of each city, about 2–10 km away, horizontally from the edge of the building complexes. The wake flow may extend to much higher levels than the building tops, depending on the incoming flow strength, the static stability in the PBL, the height of the building complexes, and the time of the day because of the strength of surface insolation.

scholarly journals Impact of an improved WRF urban canopy model on diurnal air temperature simulation over northern Taiwan

2016 ◽  
Vol 16 (3) ◽  
pp. 1809-1822 ◽  
Author(s):  
Chuan-Yao Lin ◽  
Chiung-Jui Su ◽  
Hiroyuki Kusaka ◽  
Yuko Akimoto ◽  
Yang-Fan Sheng ◽  
...  
Keyword(s):  
Land Surface ◽  
Urban Areas ◽  
Urban Canopy ◽  
Anthropogenic Heat ◽  
Surface Model ◽  
Urban Canopy Model ◽  
Simulation Performance ◽  
The Impact ◽  
Canopy Model ◽  
Northern Taiwan

Abstract. This study evaluates the impact of urbanization over northern Taiwan using the Weather Research and Forecasting (WRF) Model coupled with the Noah land-surface model and a modified urban canopy model (WRF–UCM2D). In the original UCM coupled to WRF (WRF–UCM), when the land use in the model grid is identified as "urban", the urban fraction value is fixed. Similarly, the UCM assumes the distribution of anthropogenic heat (AH) to be constant. This may not only lead to over- or underestimation of urban fraction and AH in urban and non-urban areas, but spatial variation also affects the model-estimated temperature. To overcome the abovementioned limitations and to improve the performance of the original UCM model, WRF–UCM is modified to consider the 2-D urban fraction and AH (WRF–UCM2D).The two models were found to have comparable temperature simulation performance for urban areas, but large differences in simulated results were observed for non-urban areas, especially at nighttime. WRF–UCM2D yielded a higher correlation coefficient (R2) than WRF–UCM (0.72 vs. 0.48, respectively), while bias and RMSE achieved by WRF–UCM2D were both significantly smaller than those attained by WRF–UCM (0.27 and 1.27 vs. 1.12 and 1.89, respectively). In other words, the improved model not only enhanced correlation but also reduced bias and RMSE for the nighttime data of non-urban areas. WRF–UCM2D performed much better than WRF–UCM at non-urban stations with a low urban fraction during nighttime. The improved simulation performance of WRF–UCM2D in non-urban areas is attributed to the energy exchange which enables efficient turbulence mixing at a low urban fraction. The result of this study has a crucial implication for assessing the impacts of urbanization on air quality and regional climate.

scholarly journals Sensitivity of Simulated Urban–Atmosphere Interactions in Oklahoma City to Urban Parameterization

2017 ◽  
Vol 56 (5) ◽  
pp. 1405-1430 ◽  
Author(s):  
Larissa J. Reames ◽  
David J. Stensrud
Keyword(s):  
Urban Areas ◽  
Urban Canopy ◽  
Oklahoma City ◽  
Surface Model ◽  
Urban Canopy Model ◽  
Near Surface ◽  
Modeling Studies ◽  
Suburban Cities ◽  
The City ◽  
Canopy Model

AbstractThe world’s population is increasingly concentrated in large urban areas. Many observational and modeling studies have explored how these large, population-dense cities modify local and mesoscale atmospheric phenomena. These modeling studies often use an urban canopy model to parameterize urban surfaces. However, it is unclear whether this approach is appropriate for more suburban cities, such as those found in the Great Plains. Thus, the Weather Research and Forecasting Model was run for a week over Oklahoma City, Oklahoma, and results were compared with observations. Overall, four configurations were examined. Two simulations used the Noah LSM, one with all urban areas removed (CTRL), and the other with urban areas parameterized by a modified Noah land surface model with three urban categories (LSMMOD). Additional simulations utilized a single-layer urban canopy model (SLUCM) either with default urban fraction values (SLUCM1) or with urban fractions taken from the National Land Cover Database (SLUCM2). Results from the three urban runs compared favorably to high-density temperature observations of the urban heat island. The SLUCM1 run was the most realistic, although the urban fractions applied were the least representative of Oklahoma City. All urban runs also produced a drier and deeper planetary boundary layer over the city. The prediction of near-surface winds was most problematic, with the two SLUCM runs unable to correctly reproduce reduced wind speeds over the city. The modified Noah LSM provided best overall agreement with observations and represents a reasonable option for simulating the urban effects of more-suburban cities.

Impact of urban emission on local and regional air-quality: investigating the role of the urban canopy meteorological forcing

2021 ◽  
Author(s):  
Peter Huszar ◽  
Jan Karlicky ◽  
Jana Markova ◽  
Tereza Novakova ◽  
Marina Liaskoni ◽  
...  
Keyword(s):  
Rural Areas ◽  
Urban Areas ◽  
Climate Models ◽  
Regional Scale ◽  
Urban Canopy ◽  
Meteorological Forcing ◽  
Island Effect ◽  
Regional Air Quality ◽  
Urban Emissions ◽  
The Impact

<p>Urban canopies impact the meteorological conditions in the planetary boundary layer (PBL) and above in many ways: apart from urban heat island effect, the urban breeze circulation can form. Further, the enhanced drag causes intensification of the turbulent diffusion leading to elevated PBL height and this drag, at the same time causes lower windspeeds. These changes together act as a 'meteorological forcing' for the chemical processes involing transport, diffusion and chemical transformation of urban pollutants in the urban canopy and over larger scales, therefor we use the term urban canopy meteorological forcing (UCMF). Using regional scale coupled chemistry-climate models over central Europe (involving models RegCM, CAMx and WRF-Chem),  we investigate here how the UCMF influences the urban emissions and their dispersion into regional scales. The analysis covers key pollutants as O<sub>3</sub>, NO<sub>2</sub> and PM2.5 and the 2015-2016 period. </p><p>While urban emissions contribute by about 60-80% to the total NO<sub>2</sub> and PM2.5 concentrations in cities, for ozone, they cause decrease in the urban cores and slight increase over sourrounding rural areas. More importantly, we found that if UCMF is considered, the impacts on all three pollutants are reduced, by about 20-30%. This is caused by the fact that vertical turbulence is greatly enhanced in urban areas leading to reduced fingerprint of the urban emissions (the case of NO<sub>2</sub> and PM2.5) while in case of O<sub>3</sub>, reduction of the NO<sub>2</sub> impact means smaller first-order titraltion therefor higher ozone concentrations - i.e. the ozone fingerprint of urban emissions is smaller. Our analysis showed that for evaluating the impact of urban emissions over regional scales, the meterological effects caused by the urban canopy have to be considered in modeling studies.</p>

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