High Resolution Simulation of Heat Waves in New York City using Weather Research and Forecast Model to Identify Challenges to Potential Mitigation Strategies

Abstract:

The latest IPCC report warns about the increasing frequency of heat waves in the coming years and particularly, considers them to be a serious threat to urban inhabitants. Increase in built up area which acts as an effective medium for thermal storage and reduced evaporation have changed the thermodynamic state of urbanized areas. Furthermore the presence of local effects such as urban heat island is known to amplify the effect of heat waves in cities. To address this vulnerability, several city administrations have proposed aggressive strategies to reduce near surface urban temperature. The Million Tree program and Cool Roof initiative are two such programs pursued by the NYC administrators. While these initiatives are encouraging, their applicability and resoluteness/usefulness at city scale remain untested. The three dimensional nature of the urban landscape and the heterogeneity in its physical and thermal properties impose a huge challenge to observe/model the urban microclimate. In this study the state of the art Weather Research and Forecast model has been significantly modified to improve its representation of urban energy exchange processes to study two heat wave episodes in NYC during Summer 2006. The two heat waves, which combined claimed nearly 150 lives, are simulated to study the impact of urban landscape on the near surface air temperature. Our preliminary results suggest that the urban core temperature in NYC has a footprint of around 20-30 km, suggesting that in order to reduce the near surface air temperature, surface characteristics on the order of 20-30 km need to be modified. During the heat wave episodes the highly industrialized core located to the west of NYC was highly influential in altering the City's temperature due to heat advection. Moreover, during the heat waves, the high nocturnal land surface temperatures reduced the penetrability of sea breeze, thereby keeping the air in coastal neighborhoods warmer than usual.