Extreme Heat Model Simulations

The System for Integrated Modeling of Metropolitan Extreme heat Risk (SIMMER), a NASA-funded study conducted by NCAR scientists in 2010-2014, focused on extreme heat, human health, and urban vulnerability in present and future climates. The project quantified the importance of explicitly characterizing urban properties to improve urban meteorological simulations, and the role of climate change in the future heat stress across the United States and southern Canada. Climate model simulations from SIMMER suggest high heat stress days and nights in cities across the U.S. and in some rural areas will increase substantially by the mid-21st century.

For simulating present-day and future climate and extreme heat, we used the Community Land Model (CLM) coupled to an urban canyon model to quantify present-day (PD; 1986–2005) and a projection of one possible manifestation of mid-21st century (MC; 2046–2065) rural and urban heat stress for boreal summer over the U.S. and southern Canada at fine spatial resolution (1/8° in latitude and longitude). The Weather and Research Forecasting model (WRF) was used to downscale a Community Climate System Model (CCSM4) 20th century ensemble member for PD and a CCSM4 RCP8.5 (representative concentration pathway) ensemble member for MC to provide a consistent set of atmospheric forcing variables for CLM.

We implemented five commonly used heat stress indices directly in the model. These are the National Weather Service (NWS) Heat Index, Apparent Temperature, Simplified Wet Bulb Globe Temperature, Humidex, and Discomfort Index. Heat indices are calculated for both rural (vegetation/soil) and urban areas.

High heat stress days (hot days) are defined as the number of days that the daily maximum air temperature exceeds the 95th percentile of the 1986-2005 summer rural daily maximum temperature.  As a result of this definition, the number of high heat stress days and nights for RURAL areas is always 4.6 days and nights on average (92 summer days/nights X 0.05 = 4.6).  High heat stress nights (warm nights) are defined similarly using the 1986-2005 summer rural daily minimum temperature.  These rural percentiles are applied to the urban data as well.

The data can be found at http://tds.gisclimatechange.ucar.edu/thredds/catalog/SIMMER/catalog.html

Below is an explanation of what data can be found at this site and instructions on how to access the model simulation output for future extreme heat.  All of the datasets contain the following variables:

  • Temperature (denoted as TSA in the netcdf files),
  • Apparent Temperature (APPARENT_TEMP),
  • NWS Heat Index (HEAT_INDEX),
  • Humidex (HUMIDEX),
  • Simplified Wet Bulb Globe Temperature (SWBGT), and
  • Discomfort Index (DISCOMFORT_INDEX).  


Rural and urban versions of these variables have “_R” and “_U” appended to the variable names.

How to access data

Model Data

WRF_2046-2065_jackmd_hacwstv2_RURAL_AVG_2046-2065.nc – Future 20-year average (2046-2065) for the summer months (May 1st – Sept 30th) of rural (vegetation/soil fraction of each grid cell) temperature and heat indices.  One time sample.


WRF_1986-2005_jackmd_hacwstv2_RURAL_AVG_1986-2005.nc – Present day 20-year average (1986-2005) for the summer months (May 1st – Sept 30th) of rural temperature and heat indices.One time sample.


WRF_anomaly_jackmd_hacwstv2_RURAL_AVG_mid.nc –The difference between average rural temperature and heat indices for summer months (May 1st – Sept 30th) – The difference between WRF_2046-2065_jackmd_hacwstv2_RURAL_AVG_2046-2065.nc and WRF_1986-2005_jackmd_hacwstv2_RURAL_AVG_1986-2005.nc. One time sample.


WRF_2046-2065_jackmd_hacwstv2_MIN_MAX_AVG.nc - Rural and urban daily average, daily minimum, and daily maximum temperature and heat indices for May 1, 2046 through Sept. 30, 2065. 3060 time samples (May 1, 2046 through Sept. 30, 2065).


WRF_2046-2065_climo_jackmd_hacwstv2_MIN_MAX_AVG.nc – Climatology of rural and urban daily average, daily minimum, and daily maximum temperature and heat indices for May 1, 2046 through Sept. 30, 2065.  153 time samples (May 1 through Sept. 30). 

WRF_1986-2005_2046-2065_jackmd_hacwstv2_HOTDAYS_WARMNIGHTS.nc – Rural and Urban number of hot days per summer for the present day (PD – 1986-2005) and for the mid-century (MC – 2046-2065) for temperature and heat indices.


More details can be found in:
Oleson, K.W., A. Monaghan, O. Wilhelmi, M. Barlage, N. Brunsell, J. Feddema, L. Hu, and D.F. Steinhoff, 2013: Interactions between urbanization, heat stress, and climate change, Climatic Change, , 129, 525-541, DOI:10.1007/s10584-013-0936-8.