WMO recognizes that the rapid urbanization that is currently taking place will require new types of services making best use of science and technology and considers this problem as one of the main priorities. Such Integrated Urban Weather, Environment and Climate Services (Grimmond et al., 2014) should assist cities in facing hazards such as storm surge, flooding, heat waves, and air pollution episodes, especially in changing climates.

A number of recent international studies have been initiated to explore these issues. In particular relevant experience from the European projects FUMAPEX and MEGAPOLI will be demonstrated. MEGAPOLI studies aimed to assess the impacts of megacities and large air-pollution hotspots on local, regional and global air quality; to quantify feedback mechanisms linking megacity air quality, local and regional climates, and global climate change; and to develop improved tools for predicting air pollution levels in megacities (Baklanov et al., 2010). FUMAPEX developed for the first time an integrated system encompassing emissions, urban meteorology and population exposure for urban air pollution episode forecasting, the assessment of urban air quality and health effects, and for emergency preparedness (Baklanov et al., 2007).

While important advances have been made, new interdisciplinary research studies are needed to increase our understanding of the interactions between emissions, air quality, and regional and global climates. Studies need to address both basic and applied research and bridge the spatial and temporal scales connecting local emissions, air quality and weather with climate and global atmospheric chemistry. WMO has established the Global Atmosphere Watch (GAW) Urban Research Meteorology and Environment (GURME) project (http://mce2.org/wmogurme/) which provides an important research contribution to the integrated urban services.

The numerical models most suitable for integrated urban weather, air quality and climate forecasting operational systems are the new generation of limited-area models with coupled dynamic and chemistry modules (so called Integrated Meteorology-Chemistry Models (IMCM)). These models have benefited from rapid advances in computing resources plus extensive basic science research.

Current state-of-the-art IMCMs encompass interactive chemical and physical processes, such as aerosols-clouds-radiation, coupled to a non-hydrostatic and fully compressible dynamic core that includes monotonic transport for scalars, allowing feedbacks between the chemical composition and physical properties of the atmosphere. However, simulations using fine resolutions, large domains and detailed chemistry over long time durations for the aerosol and gas/aqueous phase are still too computationally demanding due to the models’ huge complexity. Therefore, IMCM weather and climate applications must still make compromises between the spatial resolution, domain size, simulation length and degree of complexity for the chemical and aerosol mechanisms.

Representation of the urban land surface and urban sub-layer has undergone extensive development, but no scheme is capable of dealing with all of the surface exchanges. To complicate this further, the increasing resolution of models, combined with the large size of urban buildings in many cities, challenges the limits of current understanding.

Other research needs relate to secondary organic aerosols and their interactions with clouds and radiation, data assimilation that includes chemical and aerosol species, dynamic cores with multi-tracer transport efficiency capability, and the general effects of aerosols on the evolution of weather and climate. All of these areas are concerned with an efficient use of models on massively parallel computer systems.

Operational centres that base their products and services on IMCMs need to closely follow the evolution of the research and development of these coupled models, but they also need to interact with these activities. Research on basic physical and chemical processes and the development of numerical models and tools are integral and central components of reliable and accurate forecast products and services.

References

Grimmond S. et al, 2014: Towards integrated urban weather, environment and climate services. WMO Bulletin 63 (1) 10-14.

Baklanov, A. et al. 2007: Integrated systems for forecasting urban meteorology, air pollution and population exposure, ACP, 7, 855-874.

Baklanov, A. et al., 2010: MEGAPOLI: concept of multi-scale modelling of megacity impact on air quality and climate, Adv. Sci. Res., 4, 115-120.

A Sub-kilometer atmospheric modeling system with grid-spacings of 1 km and 250 m and including urban processes is currently being developed at the Meteorological Service of Canada (MSC) in order to provide more accurate weather forecasts at the city scale. A real-time forecasting system has been designed over the Greater Toronto Area (GTA) and has provided forecasts for the last year, including new thermal comfort indices. Surface physical processes are represented with the Town Energy Balance (TEB) model for the built-up covers and with the Interactions between the Surface, Biosphere, and Atmosphere (ISBA) land surface model for the natural covers. Surface temperatures for the Great Lakes are prescribed using 2-km hourly output from an ocean model. This system is devoted to help issuing alerts during the Pan-American and para-Pan-American games in Toronto during July and August 2015 (Panam TO2015).

In this study, results from different weather conditions forecasted with this new system over the GTA will be presented. As typical summertime features, the region is concerned with localized heavy rainfall, complex lake-breezes flows, and with human discomfort during heat waves. Results will be confronted against observations gathered with the dense surface and atmospheric PanAm Observational network, as well as with traditionnal EC network.

China is rapidly urbanizing. Over the last two decades, the urban population has grown to well in excess of 700 million, with a doubling of the fraction of the population living in cities (26% in 1990 to 53% today). This is resulting in areas with large and dense populations, tall buildings (in Shanghai alone the number of buildings taller than 8 stories has risen from 3,500 to more than 32,000 in the last decade) and well-documented air quality problems. The complexity of these highly urbanised environments presents enormous challenges in providing the necessary climate services to cities and regions that are weather sensitive. The dense populations (exceeding 49000 people per km2 in Shanghai, for example) mean that extreme weather events expose large numbers of people to risks including typhoons, heat stress, air quality events, etc. In this talk attention will be directed to both current capabilities and future needs for urban weather and climate services for the range of different climate zones across China, with a special focus on the multi-scale needs. The results draw on a detailed survey and interviews with those providing and using existing services.

In 2014, the population of Seoul and its surrounding metropolitan area exceeds 25 million people, which is about half of the national population of Korea. In Seoul, the population growth from one million (1942) to ten million (1998) was archived about half century and recent population of Seoul is slightly decreased since 1992 (12,245,960) despite the population increase of surrounding metropolitan area. As a result of this explosive urban growth, many kind of human-induced urban developments have changed the topography and land cover of Seoul. The changes of the land cover and the physical properties of the land surface during this period also induced the changes of air temperature, humidity, and wind. Korea also experienced a significant increase of the daily maximum temperature in major urban areas since 1960s. Many studies showed the increase of urban structure accelerated the growth in anthropogenic heats or urban heat island, which is usually called urban climatology by its climatic uniqueness. Since 2009, Climate Analysis Seoul (CAS) workbench as a rule-based urban climate analysis and evaluation tool has developed by KMA and TU Berlin to assess urban climate modifications caused by urbanization and to support the urban climate friendly decision-making in urban planning and design. During the period, project team have collaborated and improved an analytical workbench to determine the influence of buildings and vegetation areas on near-surface air temperature and wind conditions within the Seoul metropolitan area. Several results such as BioCAS, urban planning support, and urban design support were applicable. However, further challenges such expanding application area to enhance the reliability and extend the applicability, urban surface parameter development.

CAS workbench has a plan to extend the ground truth sources such as commercial telecommunication network based weather Information service, use of urban flux tower, radiosonde and LiDAR measurements field campaign. Additionally, CAS workbench will be integrated with other state-of-art models such as WRF-chem, CFD, SOLWEIG, PT to enhance the reliability and extend the applicability. Fundamentally, urban surface parameters which are more reliable and fit to Seoul metropolitan area will be developed. Finally, to make CAS workbench do its work, we shall develop more connections with neighbored projects. CAS project has a plan to integrate the developed workbench into the governmental urban planning supporting system until 2020.

It is well known that urbanization affects human thermal comfort and health, especially for vulnerable groups such as the elderly and people with established health issues. To mitigate adverse thermal comfort and accompanying excess mortality there is an urgent need of tools for forecasting urban heat on short to medium-ranged time scales. We present the setup of a prototype of such a high-resolution forecasting system which allows assessment of urban heat on neighbourhood and block scale. The forecasting system is based on simulations with the Weather Research & Forecasting (WRF) model with adapted parameterizations schemes and a novel 25-m resolution land use map, which is applied to the center of Amsterdam on a very high spatial resolution of 100 meter. These forecasts are validated against observations that were gathered during the summer of 2014 in Amsterdam. The observations include continuous observations from 25 fixed meteorological stations (temperature, humidity, and wind speed) in urban areas, bike traverses by mobile platforms (cargo bikes) equipped with state-of-the-art meteorological measurement devices (Heusinkveld et al., 2014), and stations operated by hobby meteorologists (Steeneveld et al., 2011). Besides the numerical forecasting system, we also evaluate the skill of a statistical downscaling (large-scale) algorithm that translates traditional weather forecasting system output for the rural environment of Amsterdam to the inner city. Both the validation of the forecasting system using WRF and its benchmarking against a statistical downscaling approach are performed for warm weather condition episodes that have been observed in Amsterdam during the summer of 2014.