Definitions and terminology of climate indices used
- indices computed as per year wherever applicable
Heatwaves: A heat wave is defined as an event where the minimum and maximum daily temperature both exceeds specific thresholds over a minimum number of days. The EPA definition (https://www.epa.gov/climate-indicators/climate-change-indicators-heat-waves) states
“Heat waves can be defined in many different ways. For consistency across the country, Figures 1 and 2 define a heat wave as a period of two or more consecutive days when the daily minimum apparent temperature (the actual temperature adjusted for humidity) in a particular city exceeds the 85th percentile of historical July and August temperatures (1981–2010) for that city.”
Thus, heatwave is defined as an event where the minimum and maximum daily temperature both exceed 76F & 100F respectively for a minimum of 2 days over Austin, Texas
Hot spells: A hot spell is defined as an event where the maximum daily temperature exceeds a specific threshold over a minimum number of days.
Thus, hot spell is defined as an event where the maximum daily temperature exceeds 100F for a minimum of 2 days over Austin, Texas
Calm days: The number of days with average near-surface wind speed below 2 m/s.
Cold spell days: The number of days that are part of cold spell events, defined as a sequence of 5 consecutive days with mean daily temperature below 14F.
Cold spell frequency: The number of cold spell events, defined as a sequence of 5 consecutive days with mean daily temperature below 32F.
Cold and dry days: The total number of days where “Cold” and “Dry” conditions coincide. The thresholds used are the 25th percentile of temperature and precipitation. Beniston, M. (2009). Trends in joint quantiles of temperature and precipitation in Europe since 1901 and projected for 2100. Geophysical Research Letters, 36(7).
Cold and wet days: total number of days where “cold” and “wet” conditions coincide. The thresholds used are the 25th percentile of temperature and 75th percentile of precipitation. Beniston, M. (2009). Trends in joint quantiles of temperature and precipitation in Europe since 1901 and projected for 2100. Geophysical Research Letters, 36(7).
Cold spell duration index: Number of days with at least six consecutive days where the daily minimum temperature is below the 10th percentile. Expert Team on Climate Change Detection, Monitoring and Indices (ETCCDMI).
Frost days: Number of days where daily minimum temperatures are below 32F.
Heat Index: Perceived temperature after relative humidity is taken into account. The index is only valid for temperatures above 20°C. Blazejczyk, K., Epstein, Y., Jendritzky, G., Staiger, H., & Tinz, B. (2012). Comparison of UTCI to selected thermal indices. International journal of biometeorology, 56(3), 515-535.
Heatwave frequency: Number of heat waves over a given period.
Heatwave maximum length: Maximum length of heatwaves over a given period.
Heatwave total length: Total length of heatwaves over a given period.
Hot spell frequency: Number of hot spells over a given period.
Hot spell maximum length: The longest spell of high temperatures over a given period.