CCMA3: Climate Impact studies & adaptation strategies
Characteristics of heat wave impacts for major cities in the US under current and future climate conditions
1University of North Carolina at Chapel Hill, United States of America; 2United States Environmental Protection Agency
The occurrence and duration of severe weather events is one of the indicators of climate variability and change. Heat waves have direct impacts on human health and daily activities in urban areas, especially when high pollution levels accompany elevated temperatures. We use the Weather Research Forecast (WRF) model at 12 km horizontal resolution with downscaling from the Community Climate System Model (CCSM) to simulate recent (years 2001-2003) and future (years 2048-2050) climate for nine major cities (Denver, CO; Fargo, ND; Dallas; TX; Chicago, IL; Boston, MA; New York, NY; Washington, DC; Atlanta, GA; Miami, FL) in the central and eastern United States. The future climate scenario was derived using the IPCC A1B scenario. The nine cities were chosen on the basis of their location in different climate zones based on the Koppen climate classification system, and the synoptic weather pattern during summer. We use and compare heat indices that combine temperature and humidity from WRF output to identify and analyze the heat waves in the nine cities and compare their occurrence and duration under these two different climate scenarios. We analyze meteorological parameters, during the heat wave episodes, such as boundary layer height, cloud conditions, and flow patterns in terms of backward trajectories to characterize pollution levels at these cities in association with the heat waves. We hypothesize that differences in these parameters characterize differences in the heat waves across cities. Differences in wind patterns between recent and future climate simulations also result in changes in potential regional sources of air pollution in these cities.
Impact of urban form on sunlight availability for urban farming in Asian cities at different latitudes
Urbanization process in Asia is increasing at an unprecedented rate. New towns are built in the cities’ outskirts occupying farmlands and therefore making urban population more dependent on food produced farer or from overseas.
Increasing local self-sufficiency in terms of food and energy in residential areas is one of the key measures to reduce greenhouse gases emissions as well as to mitigate and adapt to climate change. Therefore, the integration of farming areas as part of the urban tissue should be considered as one of the design parameters for new residential districts in Asian cities.
The objective of the study is to quantify the sunlight availability in a series of densities and urban morphologies located at three different latitudes and sky conditions in Asia: Singapore (1.3°N), Hanoi, Vietnam (21°N) and Beijing (39.9°N). Local food self-sufficiency are then assessed according to the sunlight requirement for some common species of fruits and vegetables. Two scenarios are considered for urban farming technologies on the ground and building facades, conventional and a combination of conventional and ‘vertical’ technologies.
Three typical residential typologies are considered: point block (25 cases), slab block and complex block (16 cases each). Each typology is assessed in terms of solar access and daylight autonomy (DA > 10klx) by using a density parameter: plot ratio and two interrelated geometry parameters: site coverage and building height. The residential area under study is 520 x 520m2.
Results show that for equatorial latitudes, the impact of density and therefore the decrease of sunlight availability is lower than in higher latitudes, however food self-sufficiency is only achieved with plot ratios (PR) lower than 2. In higher latitudes the obstruction of surrounding buildings in higher densities, considerably reduce the food self-sufficiency both on the ground and facades. The influence of facade orientation and the position of the farming areas on the ground is also analysed.
The study provides the basis for future environmental and energy assessments as well as for the elaboration of general guidelines in terms of density and urban form to achieve the required sunlight for the integration of farming areas in cities at different latitudes, especially in the East Asia region.
Impacts of a future city master plan on thermal and wind environments in Vinh city, Vietnam
1Nagoya University, Japan; 2Nikken Sekkei Civil Engineering Ltd., Japan
Vietnam (the Socialist Republic of Vietnam) is a rapidly developing country, and the recent growth rates of the economy and population are about 6 % and 1.2 %, respectively. The expansions of urban areas are progressing in the country. Under such a situation, in Vietnam, many city master plans have been proposed in these days. Recently, Nikken Sekkei Civil Engineering Ltd. proposed a city master plan for Vinh city, the capital of Nghe An Province, located in the northern part of Vietnam. The proposed city master plan targets the year of 2030 with a population of 900,000, and the total planning area covers approximately 250 km2.
In this study, we conduct future projections of the thermal and wind environments in June (hottest month), 2030 in Vinh city by introducing the proposed city master plan. The future projections are carried out using a regional atmospheric model, Weather Research and Forecasting (WRF) (Skamarock et al., 2008), combined with a pseudo-global warming method proposed by Kimura and Kitoh (2007). In particular, the changes in the local thermal and wind environments in three urban districts, i.e., central business district (CBD), existing urban district, and new urban district, by introducing the city master plan are quantitatively investigated. Additional cases with the changes in green coverage ratios (30 %, 50 %, and 60 %) and urban structures (northern-concentrated, southern-concentrated, and decentralized types) are designed, and the effects of the modifications of the city master plan on the future thermal and wind environments in Vinh city are also studied. Furthermore, the human thermal comfort in each urban district (CBD and existing and new urban districts) is assessed by using a thermal comfort index, Wet Bulb Globe Temperature (WBGT), calculated based on the results of the WRF projections.
Vulnerability to heat waves: impact of urban expansion scenarios on urban heat island and heat stress in Paris (France)
1CNRS/Météo-France, France; 2CIRED, Ecole des Ponts - ParisTech
Heat-wave risk in cities is determined both by regional climate evolutions and by cities size and shape change, because they can impact heat island effect. Land planning and urban transport policies, due to their long-lasting impact on cities shape, can therefore play a role in heat-wave risk mitigation. However, the link between these policies and resulting change in urban heat island is far from direct, and not yet clearly understood. Using Paris urban area as a case study, we show that evolutions towards a denser city could indeed lead to increased heat wave exposure when compared with urban sprawl evolutions. However, this increase depends strongly on the way heat-wave risk is measured, and on the indicators used to characterize heat island effect. Using an interdisciplinary modeling chain, including a socio-economic model of urban expansion and a physically-based model of urban climate, air temperature in the city during heat waves is simulated for five prospective scenarios of Paris urban area expansion and development. These scenarios differ in terms of land planning policies simulated, but are otherwise similar (e.g. in terms of total population evolution). Their impacts on urban heat island and population heat stress are evaluated and compared through different indicators. The urban heat island is always higher at night and hits preferentially the small area of the city centre, whereas it more widely affects the residential areas during the day. However, the concentration of population in the historic centre and the first suburbs makes these districts quite vulnerable. This is especially the case for the compact city scenario, whereas the greening strategies allow to mitigate urban heat island and consequently to insure better thermal comfort. The efficiency of such strategies is however strongly dependent on water availability for evapotranspiration of plants. Finally, it should be kept in mind that the method and choice of indicators are crucial in the process of adaptation strategies analysis.