SIMMER - Modeling of Extreme Heat Risk

The dense group of modern skyscrapers stand behind a residential area in downtown Houston, Texas, USA.
The dense group of modern skyscrapers stand behind a residential area in downtown Houston, Texas, USA.

Extreme heat is a leading cause of weather-related human mortality in the United States and in many countries world-wide. Vulnerability to extreme heat is amplified in large cities due to the urban heat island and socioeconomic diversity. Climate change is projected to increase the severity, frequency, and duration of extreme heat events, which may put more people at risk for heat-related mortality and morbidity. The System for Integrated Modeling of Metropolitan Extreme heat Risk (SIMMER) project focused on understanding extreme heat, human health, and urban vulnerability in present and future climates.  The primary goals of the SIMMER were to: 1) advance the methodology for assessing current and future urban vulnerability from heat waves through the integration of physical and social science models, research results, and NASA data; and 2) develop models and tools for building local capacity for heat hazard mitigation and climate change adaptation in the public health sector.

SIMMER employed a novel extreme heat vulnerability framework (Wilhelmi and Hayden, 2010) and focused on specific research objectives: 1) Characterize and model present and future extreme heat events at regional and local scales; 2) Improve representation of urban land cover and its accompanying radiative and thermal characteristics at local and regional scales; 3) Determine the combined impact of extreme heat and the characteristics of urban environmental and social systems on human health; and 4) Characterize  societal vulnerability and responses to extreme heat (i.e., mitigation and adaptation strategies).

The project included regional- and local-scale analyses.  The regional-scale study domain covered the contiguous United States and portions of southern Canada at ~ 15 km2. A local, intra-urban scale (1 km2; U.S. Census block group) study was conducted in Houston, Texas, the fourth largest city in the U.S. Our team collaborated with scientists and public health practitioners in Houston, as well as Toronto, Canada to ensure that the concepts, methods and models developed for Houston are applicable to other cities.

SIMMER quantified the importance of characterizing urban properties in urban meteorological simulations, and the role of adaptive capacity in understanding vulnerability to extreme heat. New methods for accurately estimating urban land surface temperature from satellite imagery have been proposed and tested. Climate model simulations project high heat stress days and nights in the U.S. will increase substantially by the mid-21st century. New statistical methods for modeling risk of heat related mortality and morbidity advance our understanding of heat risk factors, and the spatiotemporal distribution of vulnerability within cities. Results have been discussed in the context of public health policies and interventions through a stakeholder engagement process.  Currently we are employing models developed in SIMMER to better understand how climate change may change vulnerability to extreme heat.



Feddema, J. and W. Liu (2014). Seasonal and Diurnal Characteristics of Land Surface Temperature and Major Explanatory Factors in Harris County, Texas. Proceedings of the Association of American Geographers 2014 Annual Meeting, Tampa, Florida

Hart, H., Gower S., Wilhelmi, O., and Yagouti A. (2014). Integrated Models for Heat-Health Decision Making: Linking Complex Science to Policy for Heat-Health Decision Making. SIMMER Workshop Report, Toronto (Canada), 40 pp. online at:

Hayden, M., O. Wilhelmi, J. Cavanaugh, T. Greasby, D. Banerjee, and V. Nepal, (2015). Is Air- Conditioning the Answer? Understanding adaptive capacity to extreme heat: Results from a household survey in Houston, TX. To be submitted Climate Risk Management in January 2015

Heaton, M.J., Sain, S.R., Greasby, T.A., Uejio, C.K., Hayden, M.H., Monaghan, A.J., Boehnert, J., Sampson, K., Banerjee, D., Nepal, V, and Wilhelmi, O.V. (2014).  Characterizing urban vulnerability to heat stress using a spatially varying coefficient model.  Spatial and Spatio-temporal Epidemiology, 8, pp 23-33.

Heaton, M.J., Sain, S.R., Monaghan, A.J., Wilhelmi, O.V., and Hayden, M.H. (2015).  An analysis of an incomplete marked point pattern of heat-related 911 calls.  Journal of the American Statistical Association, in press DOI: 10.1080/01621459.2014.983229.

Hu, L., and Brunsell, N.A., (2013). The impact of temporal aggregation of land surface temperature data for the surface urban heat island (SUHI) monitoring. Remote Sensing of Environment, 134, 162-174.

Hu, L., Brunsell, N.A., Monaghan, A.J., Barlage, M., Wilhelmi, O.V. (2014) How can we use MODIS land surface temperature to validate long-term urban model simulations? Journal of Geophysical Research: Atmospheres, 119(6): 3185–3201

Monaghan, A.J., Hu, L., Brunsell, N.A., Barlage, M.P., and Wilhelmi, O.V. (2014). Evaluating the impact of urban morphology configurations on the accuracy of urban canopy model temperature simulations with MODIS. Journal of Geophysical Research: Atmospheres, conditionally accepted.

Oleson, K.W., Monaghan, A., Wilhelmi, O., Barlage, M., Brunsell, N., Feddema, J., Hu, L., and Steinhoff, D.F. (2013). Interactions between urbanization, heat stress, and climate change, Climatic Change, DOI 10.1007/s10584-013-0936-8.

Wilhelmi, O.V., and Hayden, M.H. (2010). Connecting people and place: a new framework for reducing urban vulnerability to extreme heat. Environmental Research Letters, 5, 014021.

Wilhelmi, O. and M. Hayden (2015) Reducing Vulnerability to Extreme Heat: Science-Policy  Interface. Chapter in: Extreme Weather, Health and Communities: An Interdisciplinary Approach to Engagement Strategies, Springer Press. 

Demuzere, M., K.W. Oleson, A.M. Coutts, G. Pigeon, and N.P.M. Van Lipzig, 2013: Simulating the surface energy balance over two contrasting urban environments using the Community Land Model Urban (CLMU), Int. J. Clim., DOI:10.1002/joc.3656.

Fischer, E.M., K.W. Oleson, and D.M. Lawrence, 2012: Contrasting urban and rural heat stress responses to climate change, Geophys. Res. Lett., 39, L03705, DOI:10.1029/2011GL050576.

Lauper, U. 2014. Risk Factors for Heat-Related Health Symptoms among Older Adults in

Houston: A Cross-Sectional Study. MPH Capstone Final Report. Colorado School of Public Health, University of Colorado. 15 pp.

Monaghan, A.J., M. Barlage, J. Boehnert, C.L. Phillips, and O.V. Wilhelmi, (2013). Overlapping interests: The impact of geographic coordinate assumptions on limited-area atmospheric model simulations. Mon. Wea. Rev., 141, 2120-2127. DOI:10.1175/MWR-D-12-00351.1.

Wilhelmi, O., de Sherbinin, A., and Hayden, M. (2012). Exposure to heat stress in urban environments: Current status and future prospects in a changing climate. Chapter 12 in Ecologies and Politics of Health, B. King and K. Crews, Eds., Routledge Press.

Zhao, L., X. Lee, R.B. Smith, and K.W. Oleson, 2014: Significant contributions of local background climate to urban heat island, Nature, 511, 216–219, doi:10.1038/nature13462


Simmer Wiki

Project team

PI: Olga Wilhelmi (Research Applications Laboratory, NCAR)
Co-PIs: Andrew Monaghan and Mary Hayden (Research Applications Laboratory, NCAR)
Stephan Sain (Institute for Mathematics Applied to Geosciences, NCAR)
Keith Oleson (Climate and Global Dynamics, NCAR)
Michael Barlage (Research Applications Laboratory, NCAR)
Johannes J. Feddema (Department of Geography, University of Kansas)
Nathaniel Brunsell (Department of Geography, University of Kansas)


Sunset reflecting off Toronto's skyscrapers.

Chris Uejio (CDC/NCAR),
Deborah Banerjee (Houston Department of Health and Human Services)
Marshall Shepherd (University of Georgia)
Eric Fetzer (NASA JPL)
Alex de Sherbinin (CIESIN, Columbia University)
Claus Rinner (Ryerson University)
Adebowale Awosika-Olumo (Houston Department of Health and Human Services)
Ugis Bickis (Climate Change and Health Office, Health Canada HQ, Ottawa)
Abderrahmane Yagouti (Climate Change and Health Office, Health Canada HQ, Ottawa)
Monica Campbell (Environmental Protection Office, Toronto Public Health)
Stephanie Gower (Environmental Protection Office, Toronto Public Health)
 Ciara De Jong (Toronto Environment Office, City of Toronto)
Robert Harriss (HARC)
Jennifer Boehnert (NCAR)
Kevin Sampson (NCAR)


National Aeronautics and Space Administration


Please direct questions/comments about this page to:

Olga Wilhelmi

Head of GIS Program