POSTER 10: UCP - Interaction between cities and mesoscale flows and precipitations
Modeling impacts of New-York-City metropolitan land cover on regional precipitation
1Brookhaven National Laboratory, Upton, NY, United States of America; 2The City College of New York, New York, NY, United States of America; 3San José State University, San Jose, CA, United States of America; 4NOAA/National Weather Service Forecast Office- New York, NY, United States of America
Metropolitan land cover typically comprises a vast array of densely deployed high buildings, forming strong barriers to atmospheric circulations. This study uses the community mesoscale Weather Research and Forecasting (WRF) model and an urbanized WRF (uWRF) model to investigate impacts of urban building barriers on regional precipitation distributions. A storm with extreme precipitation, moving from west to east of New-York-City (NYC), in September 2010 was chosen for this investigation. Preliminary results show that the metropolitan land cover significantly influenced the precipitation distribution over this region. Modeled results from both the WRF and uWRF show a storm splitting effect due to the presence of the city, that is, much reduced precipitation over NYC and over downwind suburban Long Island, and enhanced precipitation on the periphery of NYC, compared to a forest land cover that replaced NYC. Results concur with findings from observations based on previous studies and existing sensors networks. The uWRF simulated precipitation is closer to observations, as compared to the WRF results, although both the models tend to underpredict observed precipitation. The forest land cover engenders a much larger latent heat flux, as compared to the urban land cover, which could explain the reduced precipitation over the city and its downwind suburb. Further analyses are under way. Results from this study should be useful for enhancing our understanding of impacts of metropolitan land cover on regional precipitation, and of the WRF’s and uWRF’s capabilities in simulating such impacts.
Characteristics of the spatiotemporal pattern of Extreme Rainfall event over the state of Uttarakhand, India
1Indian Institute of Remote Sensing, Indian Space Research Organization, Dehradun, India; 2ITC, University of Twente, The Netherlands
The Himalayan state of Uttarakhand is experiencing urbanization and economic growth at an unprecedented rate. Being an alpine state with altitude ranging from 175m to 7409 m above mean sea level and average annual rainfall of approximately 1494.72 mm, it is highly prone to cloudbursts, associated flash floods and landslides. However, the complex young folds and the fragile mountain eco-systems are being steadily agitated due to the increasing population and rapid haphazard urbanization. Consequently, the state witnesses colossal disasters initiated by cloudbursts almost every year. The multi-date extreme rainfall event (ERE) during June 15-17, 2013 resulting in devastating floods known as the Kedarnath Disaster was one such noteworthy disaster also termed as ‘The Himalayan Tsunami’ due to its sheer enormity, is widely acknowledged as India’s worst natural disaster since 2004. It had resulted in thousands of fatalities and missing people and the complete wipe-out of entire towns and several villages. Though Kedarnath lies in an ecologically sensitive zone, researchers unanimously agree on rampant construction and mushrooming hotels as a prime cause behind huge death toll.
The major reason behind such disasters is the lack of study of such weather phenomenon attributing to inadequate reliable rain networks in the remote mountainous regions and inability to predict the weather extremes well in advance. Remote sensing has proved useful in such studies. In this study, we want to determine the spatiotemporal trend of the EREs and its association with elevation over the state Uttarakhand of India.
A conventional definition of cloudburst defines it as a transitory localized phenomenon featuring very high intensity rainfall over a small area of 20-30 km2. As many researchers have come up with objective definitions, we propose any rainfall event above 98, 99 and 99.99 percentiles can be classified as heavy and very heavy rainfall events respectively.
The gridded dataset of TRMM (Tropical Rainfall Measuring Mission) 3B42 v7 3-hourly rainfall product with resolution 0.25° x 0.25° for the past 16 years from 1998 to 2013 has been used for the present analysis. The elevation has been derived from Shuttle Radar Topography Mission (SRTM) with a spatial resolution of 90 m. The state receives 86% of its annual rainfall during the Indian summer monsoon, our study exclusively focuses on monsoon months i.e. June, July, August and September.
A rainfall is a point process which has high variability within a small spatiotemporal extent. Therefore, we aim to calculate 98, 99 and 99.99 percentiles for each grid based on the measurement of 16 years period and observe the frequency of EREs on each grid. Based on our analysis, we observe that the lower altitude areas have higher rainfall intensities associated with each percentile compared to higher altitude regions. We also observed that the South-East and North-West regions experience heavy rainfall as compared to other regions. Interestingly these are the regions undergoing rapid urbanization and industrialization. Another intriguing observation points out that few higher altitude regions which usually have as low rainfall intensities as <80 mm/day associated with 98 and 99 percentiles, show sudden jump of >150 mm/day for 99.99 percentile.
In addition to the above results, the rainfall intensities associated with 98, 99 and 99.99 percentiles for each year in combination with hourly analysis will also be presented with greater details in the conference. We are also interested in doing a comparative study between land use land cover (LULC) and the rainfall analysis.
The dearth of research papers on the climate extremes over the region with respect to increasing urbanization and state’s proclivity for disasters has been the principal driving force behind our research.
Acknowledgement: The present work is a part of EOAM project, the authors thankfully acknowledged the support and encouragement provided by Head MASD, Group Director ER & SS Group and Director IIRS to carry out the research work. Authors are also grateful to CGIAR-CSI (SRTM) and NASA (TRMM 3B42 v7) for providing data online for research purpose.
ANALYSIS OF CLOUD PROPERTIES IN THE MATSUYAMA PLAIN USING DOWNWARD SOLAR RADIATION DATASET FROM A GEOSTATIONARY SATELLITE
Ehime University, Japan
Clouds play very important role in the earth’s climate and energy balance. Reflection of solar radiation by cloud makes the earth surface cool whereas, emitting and absorption of terrestrial radiation keep the earth surface warm. Therefore, cloud is one of the important elements in earth energy system, and it is necessary to know its property for the better understanding of climate and environmental change. This study puts an effort to know the impact of geographical landscape and land use variation on clouds.
Based on satellite downwards short wave radiation data in Matsuyama plane, the thickness trend of cloud was found to be increasing with the rise in the elevation. In this study, downward shortwave radiation was compares in different geographical landscapes and land use by relating it with cloud. The comparison was conducted by calculating the decrease ratio of downward SW radiation and its difference. The objective of the study was to analyze the difference in impact of land use and the geographical landscape variation on clouds.
The comparison between mountain and the plane suggested that the clouds are likely to thicker in mountains than in plane. The tendency of thickening rises up from the morning until afternoon and decreases accordingly. This may be because of the orographic lifting of the air parcel due to the blockage of sea breeze by mountain, forming cloud on the top of the mountain. Another compression between Coastal and noncoastal describes that the cloud is thicker in the noncoastal area than coastal area. This may be due to the lifting of the air parcel by the convergence of the northern and the south wind in Matsuyama plane forming the cloud above the noncoastal area. Finally, the comparison between urban and rural was done for two different months, September (summer) and January (winter). The comparison on September suggested that the cloud is likely to be thicker at the urban area in the afternoon then rural area. This may be because of lower wind speed and higher temperature in urban area. The warmer air parcel rises up under the influence of convection and cools due to the altitude effect forming cloud above the urban area. This is experimentally supported by the field measurement, where urban surface heat flux is larger than that in rural areas. The comparison on January suggests that the trend of cloud formation is likely to occur almost similar throughout the morning up to the late afternoon in both rural and urban area compared to the summer analysis. It may be because of the surface air temperature and humidity intensity difference between urban and rural areas according to the seasonal variation. Both winter and summer results are supported by Moriwaki et al. result. Moriwaki et al.2) have suggested that “when the wind direction is west to east, the surface air temperature and humidity at urban and rural will tend to be different and the difference will be maintained aloft through vertical convection in each area. In contrast, when the wind direction is northerly or southerly, the air is transported across the border of land use and thus the difference between two areas become low”. In the Matsuyama plain, the westerly and easterly wind is prominent in summer, whereas the northerly and southerly wind is dominant in winter due to monsoon carrying wind.
1. Moriwaki, R., Watanabe, K., Morimoto, K.: Urban dry island phenomenon and its impact on cloud base level, Journal of JSCE, Vol.1, pp. 521-529, 2013.
URBAN DRY ISLAND PHENOMENON AND ITS IMPACT ON CLOUD BASE LEVEL AND SOLAR RADIATION IN MATSUYAMA PLANE
Ehime University, Japan
Matsuyama plain, Japan has an obvious contrast of land use in urban and rural area. The purposes of this study investigate the features of Urban Dry Island (UDI), Clouds base level, and solar radiation. On the basis of field measurements in the Matsuyama Plain, the following main outcomes are obtained. The urban absolute humidity was lower than rural absolute humidity. Following the manner of urban heat island phenomenon, we call this phenomenon “urban dry island” (UDI). The UDI phenomenon was significantly found at the daytime during the fine day due to the difference in water vapor fluxes at urban and rural sites. Cloud base level over urban area was higher than that over rural area when wind blew along the border of the abrupt change of land use. This was demonstrated by lifted condensation level, which was estimated from the surface air temperature and water vapor content. Solar radiation over urban area tends to be smaller than that over the rural area during afternoon of days with a percentage of sunshine ranging from 50% to 80%. This was demonstrated by the development of mixing layer estimated from surface heat flux.
Keywords: urban dry island, cloud base level, solar radiation, urban heat island phenomenon, surface heat flux, lifted condensation level
Observations and numerical simulations for TOMACS urban heavy rainfall cases
1Meteorological Research Institute, Japan; 2National Defense Academy; 3Chiba Institute of Technology
Recent increase in severe weather such as torrential rain, which may be due to the global warming, can cause extensive damages to large cities. Tokyo Metropolitan Area Convection Study for Extreme Weather Resilient Cities (TOMACS) has been conducted for the sake of better understanding of the process and mechanism of extreme weather in urban area in the context of disaster prevention. The TOMACS project also aims to develop improved monitoring and predicting systems of extreme phenomena. Observations took place with a variety of techniques including Radar network, radio sonde, GPS precipitable water observing system, and Doppler Lidar. During the TOMACS intensive observation period in 2011-2013 summers, atmospheric environment of several heavy rainfalls was observed by means of radiosonde soundings in the Tokyo metropolitan area. The radiosonde observations carried out in higher time and space resolution than the operational ones and captured variations in thermal and dynamic characteristics in the atmospheric boundary layer. Numerical simulations were conducted for these events with the Non-Hydrostatic Model of the Japan Meteorological Agency (JMA-NHM) incorporating the Square Prism Urban Canopy scheme (SPUC). Formation and development processes of convective systems were investigated using the observation and simulation results. In particular, we discuss the atmospheric environment of extremely developed and moderately developed convective systems focusing on the similarities and differences between the two cases.
Interaction of Singapore and Johor Bahru on urban climate during monsoon seasons
1University of Graz, Austria; 2Hiroshima University, Japan; 3Saitama University, Japan
Urban development in rapidly urbanizing regions requires comprehensive planning and consideration on local characteristics. Tropical cities are particularly affected by increasing air temperature in relatively densely built-up areas, since increase in temperature is associated with higher cooling loads and hence higher energy consumption. Many major cities developed therefore strategies to ensure sustainable urban development. However, in regard to urban climate, proposed development strategies are limited to the borders of the city or the country. A comprehensive understanding of interactions between two major cities on their urban climate needs further investigation.
This study aims to assess the interaction between the development in Singapore and Johor Bahru on urban climate and formation of Urban Heat Island (UHI). Despite relatively low wind speed, the characteristic wind flow pattern in this region is expected to impact the occurrence of UHIs in Singapore and Johor Bahru and provide some understanding on cross-boundary mitigation strategies.
Johor Bahru is located in the southern-most tip of Peninsular Malaysia and is the second largest city after Kuala Lumpur. Singapore is a city-state, located on an island south of Johor Bahru. Both cities are separated by the Strait of Johor. Recently, Johor Bahru is experiencing rapid development in the course of the implementation of the Comprehensive Development Plan (CDP) 2006. The CDP proposes strategic interventions to promote economic growth and improve quality of life in South Johor. Singapore, in contrast, almost reached its physical limits for further development. By 2030, Singapore will develop about 7.3% of land to meet its future land requirements.
The wind flow over Peninsular Malaysia is determined by southwest and northeast monsoon, and by intermonsoon seasons. From June to September, southwesterly winds prevail, whereas from November to March the prevailing wind direction is northeast. In the intermonsoon season, wind flow is light and variable. Uniform and periodic changes of wind flow during summer and winter were of particular interest for this study. During summer, Singapore benefits from its maritime location with relative cool winds coming from the sea. Over Singapore Island, air heats up and proceeds to Johor Bahru. Thus, Johor Bahru might be cut off from the sea breeze. During winter, the process reverses and air heats up over Johor Bahru, northern and northeastern parts of Singapore might be negatively affected by the warm air carried across the Strait of Johor.
The impact assessment of wind flow on urban climate and UHI formation was conducted using a Weather Research and Forecasting (WRF) model with a spatial resolution of 0.5 km. The urban climate in the research area was modelled for climatic conditions in the period from 9 to 15 June 2009 (SW monsoon) and from 4 to 10 February 2009 (NE monsoon).
The preliminary modelling results showed the impact of sea breeze on the southwestern coast of Singapore during SW monsoon. The average temperature at the coast was 2 to 3 °C lower than in the northeastern part of Singapore. In Johor Bahru, the formation of UHIs over the CBD and the industrial area east of it was observed. The maximum UHI intensity reached up to 2.8 °C. The Johor Strait appeared to be an effective buffer zone between both cities. During NE monsoon, formation of UHIs occurred in the CBD of Singapore and the industrial area west of it with maximum UHI intensity of around 3 to 4 °C. The eastern part of Singapore experienced lower temperatures than in the southwestern part. The formation of UHI in Johor Bahru occurred mainly in the CBD. The air temperature of the Johor Strait between CBD (Johor Bahru) and northern coast of Singapore was 1 to 2 °C higher than in surrounding areas. The buffer effect of the Johor Strait was interrupted, so that warm air was carried over the strait. Therefore, mitigation of UHI formation in Johor Bahru might especially benefit the northern coast of Singapore during NE monsoon.
land use changes of eastern egyptian desert for suastainable urban development
Cairo University Egypt, Egypt
Egypt is one of the hot spot areas affected negatively by climate change. As it has a limited cultivated land, and water availability can perform sustainable development. The present work employ regional climate model (RgcM4) to test the effete of greening part of eastern desert on the local circulation of the wind and consequently the precipitation pattern over this area. The preliminary results after some validation over this area provided a high sensitivity to this changes by forecasts. The paper present change in surface energy fluxes before and after the experiment.
Key words: Land use, RgcM4, Eastern Egyptian desert.
Effect of the River in the Urban Area on Local Climate in the Vicinity of the River
Meijo University, Japan
It has been generally recognized that rivers running through the urban area may mediate urban climate because cool air produced in the river course by water evaporation or cool air from the ocean is delivered from or through the river course. However, since rivers in the urban area run on deeper surface and the side walls of the river course are mostly made of concrete like an artificial narrow canyon, air temperature in the river course (Tar) may not be lower but higher than the vicinity of the river. To prove this hypothesis, we made observation on local climate of the river course and vicinity in Nagoya city, Japan.
Five locations were selected on Ueda River which runs in the east of Nagoya city, and 2 locations were selected on Yada River which runs in the rural area east of Nagoya city. Metrological factors such as air temperature, relative humidity, wind velocity, wind direction, solar irradiation and radiation reflected from the ground were continuously measured from 10:00 to 16:00 at the lowest surface in the river course, and consecutively at 3 locations which were situated at 20 m, 40m, and 60 m from the edge of the river moat.
Observation in the river course demonstrated that absolute humidity became highest in the noon and wind direction often differs from that the river flow direction. Statistical analyses indicated that Tar was significantly (p<0.01) correlated with a flow speed and the amount of river water. Observation in the vicinity of the river demonstrated that cool air from the river course was delivered only in the morning. Statistical analyses showed that difference between Tar and air temperature in the vicinity locations was significantly (p<0.01) correlated with river width.
Idealized experiments on the development of urban warming under various geographical conditions using a meso-scale meteorological model
1Disaster Prevention Research Institute, Kyoto University, JAPAN; 2Graduate School of Science, Kyoto University, JAPAN
Geographical characteristics make a specific local circulation for each characteristic, for example sea breeze over a coastal city. The circulation around urban area affects a diurnal change of urban atmosphere, and also long-term climate change. Because the characteristics vary the effect of urbanization, areas with the same speed of urbanization would show the different climate depending on the characteristics. It means the comparison of urban effect is difficult among cities with the different characteristics. The geographical effects have been investigated on the diurnal change in urban areas, on the other hand, insufficiency on the climatological change as an urban climate. Urban warming is well known as that the more urbanization advances, the greater warming the time series shows. The climate in mature cities, however, has shown gradual warming, that is, rising rate of temperature could change in each stage of urbanization.
In this study, to clarify trends of urban warming with urbanization for the cities with different geographical characteristics, developments of urban climate were represented using a meso-scale meteorological model. Urban areas with three different levels of urbanization were set up to describe the urban development. Geographical characteristics were applied as three simple geographical conditions to the boundary conditions. Each city is an inland city which locates in a flat green area, a coastal city of which the boundary shares with sea area, and a basin city which mountains with the height of 1500 m dominate.
In an inland city, the mixing layer grows up as the urbanization near surface in the night, and thus, the temperature change seems to become small. The tendency of temperature rises during the nighttime decelerates with developing of urbanization. By contrast, the tendency during the daytime accelerates because it takes time for a heat island circulation to reach inside of the urban area when the city expands with urbanization. For the formation in a coastal city, the temperature rise amount is smaller than that of the inland city. Sea and land breeze play an important role in the trend of urban climate in the coastal city. Thickness of sea breeze decides the height of mixing layer over the city during the day, especially in summer. When the height of the layer is fixed, temperature rises with increasing of heat diffusion from urban area. Therefore the rise of daily maximum temperature accelerates. For the formation in a basin city, strong stable layer exists over the urban area and the development of mixing layer by heat from the urban constricts in the layer. Because of thermal storage increases in the basin with urbanization, the tendency of the temperature rise accelerates. The geographical effects appear most significantly on the daily minimum temperature. The temperature difference between the coastal city and the inland city is larger than that between the basin city and the inland city for all stage of urban development. The trends of daily mean temperature rise show a deceleration for the inland city and the coastal city and acceleration for the basin city.
effect of small-scale surface heterogeneities and buildings on radiation fog
1CNRM-GAME, France; 2Laboratoire d'aerologie, France
Large-eddy simulations of radiation fog were performed over an airport area to study the effect of urban canopy on fog.
These LES simulations were performed with the Meso-NH research model at very high resolution : 1.5 m in the horizontal and 1 m in the vertical and over a domain 4.5 km x 1.5 km.
The blocking effect of the airport buildings led to strong wind shear and consequently to the production of TKE.
The airport buildings also had a strong effect on vertical velocity, with a subsidence region behind the buildings.
Both the increase of turbulence and the vertical velocity strongly modified the fog formation.
The fog layer took more time to form in the airport area
but the increase in turbulence facilitated the vertical development of the fog layer.
The fog took 1.5 h to form over the whole simulated airport area.
The fog height was heterogeneous during the formation phase, with the formation of very low clouds locally.
The effect of airport buildings on vertical velocity could explain these heterogeneities of the fog height. During the mature phase of the fog, the buildings had little impact on the fog layer characteristics.
The fog dynamics were mainly controlled by processes at its top.
These results suggests that the inclusion of high levels of detail in the building representation remains important for the local forecasting of fog formation.
Particularly, small scale heterogeneities can explain the spatial variability of fog formation.
Small scale variability of urban canopy seems to be necessary to take into account for local and accurate forecast of fog formation over airport areas.
The altered hydrologic cycle of the Mexico City basin.
The rapid urban growth of Mexico City has led to an environmental crisis. Its population increased from around 2 million people at the beginning of the twentieth century to more than 20 million at present. The rapid expansion of the urban area, from only 100 km2 to more than 2000 km2, has resulted in an Urban Heat Island where mean temperature has increased in more than 3ºC in 100 years. Even more, precipitation in the western part of the city has changed from around 600 mm/year to around 900 mm/year at present, as a result of a larger number of extreme precipitation events (more than 20 mm/day). The urbanization to the foothills of the surrounding mountains increases the runoff to the Valley, which in turn results in more frequent urban localized floods. This occurs in the context to a generalized water crisis in the region. The recovery of the ecosystem services may provide a relief of the changed hydrologic cycle for the city.