October 1, 2004— Although cities themselves represent a very small fraction of the Earth's surface area, the world's population has become increasingly urbanized and is now affected by both natural weather and climate patterns, as well as local-scale (weather and climate) effects derived from the urbanization process itself. Urban meteorology reveals how weather and climate interact with all aspects of the urban environment, and provides insight to help better manage cities and respond to natural and human-induced hazards.

“With nearly two-thirds of the U.S. population living in urban areas, there is a rapidly growing need to understand and predict meteorological conditions in these areas,” said James R. Mahoney, Ph.D., assistant secretary of commerce for oceans and atmosphere and deputy NOAA administrator. “Special concerns in urban areas include severe weather, air quality, dispersion characteristics, climate and urban runoff — most of which impose new demands on forecast models. Several NOAA offices are already engaged in work and partnerships focusing on this specialized and relatively new area of meteorology.”

Weather and the Urban Environment
Not only are urban areas affected by weather and climate, but they also exert their own unique influence on local-scale weather and climate. The climate in and around urban areas is altered in part by the modifications humans make during urbanization. Naturally vegetated surfaces are replaced by buildings and paved streets that seal the Earth’s surface and add vertical dimension to the environment. These changes affect the absorption of solar radiation/heat storage capabilities, evaporation rates and surface temperature (often creating what is known as a heat island effect), as well as local turbulence and wind patterns. This, in turn, can drastically alter near-surface atmospheric conditions. Human activities in urban areas also generate water vapor, heat and pollutant emissions that directly impact the temperature, humidity, air quality and visibility in urban areas. On slightly larger scales, urbanization can also lead to changes in precipitation above and downwind of developed areas. Urban life is also responsible for much of the greenhouse gas emissions that may be altering climate on regional to global scales. In fact, urbanization alters just about every aspect of climate and weather in cities.

Challenges in Urban Meteorology: A Forum for Users and Providers
On Sept. 21-23, 2004, NOAA's Federal Coordinator for Meteorology, Samuel P. Williamson, hosted a forum entitled “Challenges in Urban Meteorology: A Forum for Users and Providers” in collaboration with the Department of Homeland Security, Science and Technology Directorate at the Doubletree Hotel in Rockville, Md. The forum was attended by meteorologists, emergency managers, scientists and members of the private sector, who discussed strategies to meet emerging problems and the unique challenges associated with public health and safety in highly populated urban areas. (Click on NOAA image below right for a more detailed view of the tracks of all recorded tornadoes occurring within the immediate Oklahoma City area from 1890 to 2000.)

Why address Urban Meteorology Now?
Three factors have come together to make this the optimal time to address key issues in urban meteorology:

• Advances in observing systems, weather forecast models and information technologies provide opportunities to address urban weather needs in ways not feasible just a decade ago.
• Recent national and international events have heightened attention to potential acts of terrorism, particularly in large urban areas. Chemical, biological, radiological and nuclear releases (whether intentional or accidental) threaten public health and safety. Atmospheric transport and diffusion models used to predict the behavior of these harmful substances depends on inputs from urban environmental observations.
• Health problems associated with extremes in urban weather and climate can threaten human health and strain response services. Other urban conditions, such as air and water pollution can have long-term cumulative effects on health.

Critical Urban Meteorology Issues
Many of the most pressing and serious issues fall within five areas of environmental concern: severe weather, homeland security, air quality, water quality and climate change:

• Severe weather in urbanized areas includes major winter storms, hurricanes, flash flooding due to locally heavy precipitation, regional flooding along waterways, periods of extreme high or low temperature and tornadoes.
• Homeland security issues relate to the dispersion of hazardous materials by atmospheric and/or waterborne transport. High density urban populations and the effects of urban topography on the local wind field combine to make accurate fine-scale prediction of plume movement and concentration essential, but extremely difficult.
• Air quality is affected by atmospheric pollutants resulting from human activities, including the effects of these pollutants on naturally occurring airborne substances. Urban traffic and the local, fine-scale effects of the constructed environment on air movement can exacerbate the impact of air pollutants on human health. Urban communities are also a major source of air pollution in downwind rural and natural ecosystems.
• Water quality is affected by the role of the atmosphere and precipitation in the Earth’s water cycle. Many airborne pollutants are eventually washed out of the air and can be transported to surface or ground waters and precipitation events affect the load of contaminants carried into urban water supplies and/or away from urban communities as storm drainage.
• Climate issues for urban communities include the effects of natural variations in climate cycles (e.g., El Niño) and of anthropogenic influences on climate. Local and regional variations in seasonal conditions and weather patterns are critical for long-term urban planning and management.

Crosscutting Themes
The following crosscutting themes are common to most (if not all) of the major urban meteorological issues, and therefore should be taken into account when developing weather and climate products/services for urban areas:

• Regional ecosystem planning and management (e.g., urban impacts of wildfires, waterway and coastal pollution impacts on aquatic/marine systems, regional air and water quality issues);
• Research and technology tools, including models to predict weather conditions, atmospheric transport and dispersion, and climate variations on local to regional scales;
• Integrated observation systems to support and validate these models, and provide data on current conditions;
• Education, outreach and training for the entire range of current and potential users of urban environmental data;
• Risk management and risk communication for time scales ranging from emergency preparedness (rapid response) and severe weather (intermediate time scales) to seasonal and generational climate fluctuations (long-term planning);
• Public health and safety, including immediate and longer term health effects;
• Information dissemination and interpretation technologies, systems and interfaces to move data efficiently from source to appropriate users, in useful formats;
• Surface transportation and
• Business continuity planning.

Meeting the Challenge
To manage the risks to public safety, health and property, urban decision makers are demanding more accurate and specific weather and climate information. In his luncheon address to the forum, Dr. Mahoney stressed that we need to find a system solution if we are to deliver the improved weather and climate services required by urban leaders and managers. We must identify the problems we are trying to solve within the context of the whole urban system we support and then optimize the solution. Approaching urban meteorology in a specialized, interdisciplinary manner will provide an integrated response to the users’ demands for better, more useful information.

Current Capabilities In Weather and Climate Products And Services
Weather/climate products and services that address urban meteorology issues are found all across federal agencies, state and local governments, industries and universities. Some of NOAA’s overarching urban meteorology capabilities are described below:

• The NOAA Weather Service operates weather and climate observation networks to serve national needs and meet international obligations. It collects weather and climate data, checks data quality, stores data for access by other users and assimilates data into numerical and other models to develop forecasts, advisories and warnings.
• The NOAA Environmental Satellite, Data and Information Service manages the U.S. environmental satellite systems used in civil operations. It also maintains archives of meteorological, oceanographic, geophysical and solar-terrestrial data.
• NOAA Research supports meteorological, oceanographic and space missions, including improving observation and forecast tools for severe weather and airborne volcanic ash.
• The NOAA Ocean Service acquires data on water levels, currents, winds and other parameters to provide information products essential to marine transportation in coastal areas and ports.

Advances in urban meteorology will save lives and property, and benefit urban commerce. NOAA will continue to advance its urban meteorology capabilities and assist in the coordination of a federal strategy to address the weather-related needs of urban communities.

Relevant Web Sites
NOAA

NOAA National Weather Service

NOAA Office of the Federal Coordinator for Meteorology

OFFICE OF THE FEDERAL COORDINATOR FOR METEOROLOGY
HOSTS URBAN METEOROLOGY FORUM (Press Release, September 2004)

Presentations from "CHALLENGES IN URBAN METEOROLOGY:
A FORUM FOR USERS AND PROVIDERS"

Media Contact:
Greg Romano, NOAA National Weather Service, (301) 713-0622