Simulating the Urban Heat Island Augmented with a Heat Wave Episode Using ICTP RegCM4.7 in a Mega-Urban Structure of Karachi, Pakistan

Document Type : Regular Article

Authors

1 Computational Meteorologist, Numerical Weather Prediction Center, Pakistan Meteorological Department, Islamabad, Pakistan

2 Senior Scientist, Earth System Physics, The Abdus Salam International Centre for Theoretical Physics, Trieste, Italy

3 Senior Meteorologist, Numerical Weather Prediction Center, Pakistan Meteorological Department, Islamabad, Pakistan

4 Post Doc Researcher, CEN, Institute of Geography, University of Hamburg, Hamburg, Germany

5 Electronic Engineer, Numerical Weather Prediction Center, Pakistan Meteorological Department, Islamabad, Pakistan

Abstract

The metropolis of Karachi, with a density of around 4000 persons/km2 at present, is going through unprecedented urbanization and population growth, which can augment Urban Heat Island (UHI) triggered heat wave impacts on life and living. Here, we investigate skill of Regional Climate Model version 4.7 (RegCM4.7) in simulating 2015 heat wave episode in southern Pakistan by dynamically downscaling ERA-Interim reanalysis at 10km resolution and switching on the urban parameterization in the employed land surface scheme. Our results suggest that the RegCM4.7 has successfully reproduced the overall conditions of the 2015 heat wave. For instance simulated surface temperature maxima is seen well above 50°C for at least three consecutive days along the austere heat wave duration. Also, extended sustenance of a ridge in locality of the Karachi, as well as a low pressure system in adjacent Arabian Sea is seen to restrain normal drift of sea-breeze to the coastal city, in the simulated output. The National Weather Service (NWS) based heat index derived from the simulation is seen to remain well above 124°F during the whole heat wave period, placing the city in an “Extreme Danger” class of discomfort and high vulnerability to heat stroke. The UHI integrated RegCM4.7 is hence recommended for use in modelling to help in adaptation strategies against occurrences of such heat wave events in future.

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