The Climdex project offers a range of climate extremes indices. These indices are annual or monthly statistics of modelled or observed climate data. Here you can find descriptions and formulae for each of the indices.

The Climdex project offers a range of climate extremes indices. These indices are annual or monthly statistics of modelled or observed climate data. Here you can find descriptions and formulae for each of the indices.

Find out more about useful indices per sector

Annual count of days when `T``N` (daily minimum temperature) < 0°C. Let `T``N`_{i}` _{j}` be daily minimum temperature on day

Annual count of days when `T``X` (daily maximum temperature) > 25°C. Let `T``X`_{i}` _{j}` be daily minimum temperature on day

Annual count of days when TX (daily maximum temperature) < 0 °C. Let `T``X`_{i}` _{j}`be daily maximum temperature on day

Annual count of days when TN (daily minimum temperature) > 20 °C. Let `T``N`_{i}` _{j}` be daily minimum temperature on day

Annual* count between the first span of at least 6 days with daily mean temperature TG >5 °C and the first span after July 1^{st} (Jan 1^{st} in SH) of 6 days with TG <5 °C.

Let `T``G`_{i}` _{j}` be daily mean temperature on day

* Annual means Jan 1^{st} to Dec 31^{st} in the Northern Hemisphere (NH); July 1^{st} to June 30^{th} in the Southern Hemisphere (SH).

Let `T``X`` _{x}` be the daily maximum temperatures in month

Let `T``N`` _{x}` be the daily minimum temperatures in month

Let *TX _{n} * be the daily maximum temperatures in month

Let *TN _{n} * be the daily minimum temperatures in month

Let `TN _{ij}` be the daily minimum temperature on day

Let `TX _{ij}` be the daily maximum temperature on day

Let `TN _{ij}` be the daily minimum temperature on day

Let `TX _{ij}` be the daily maximum temperature on day

Let `TX _{ij}` be the daily maximum temperature on day

Let `TN _{ij}` be the daily maximum temperature on day

Let `TX _{ij}` and

Let `T``X`` _{x}` be the daily maximum temperature in month

Annual sum of `TM` - `n`, where `n` is a user-defined, location-specific base temperature and `TM` > `n`. A measure of the energy demand needed to cool a building.

Annual sum of `TM` - `n`, where `n` is a user-defined, location-specific base temperature and `TM` > `n`. A measure of the energy demand needed to cool a building.

Annual sum of `n` - `TM`, where `n` is a user-defined, location-specific base temperature and `TM` < `n`. A measure of the energy demand needed to heat a building.

Number of days when `TM` (daily mean temperature) ≥ 5 °C.

Number of days when `TM` (daily mean temperature) < 5 °C.

Number of days when `TM` (daily mean temperature) ≥ 10 °C.

Number of days when `TM` (daily mean temperature) < 10 °C.

The mean daily mean temperature.

The mean daily maximum temperature.

The mean daily minimum temperature.

Number of days when `TX` ≥ 30 ≥C.

Number of days when `TX` ≥ 35 ≥C.

Percentage of days when `TX` > 50th percentile.

The number of days when `TN` < 2 °C.

The number of days when `TN` < -2 °C.

The number of days when `TN` < -20 °C.

Let *RR _{ij}* be the daily precipitation amount on day

Let * RR _{kj}* be the precipitation amount for the 5-day interval ending

Measure of "drought" using the Standardised Precipitation Index on time scales of 3, 6 and 12 months. A drought measure specified as a precipitation deficit. See McKee et al. (1993) and the SPI User Guide (World Meteorological Organization 2012) for details.

Measure of "drought" using the Standardised Precipitation Evapotranspiration Index on time scales of 3, 6 and 12 months. A drought measure specified using precipitation and evaporation. See Vicente-Serrano et al. (2010) for details.

Let *RR _{wj}* be the daily precipitation amount on wet days,

Let *RR _{ij}* be the daily precipitation amount on day

Let *RR _{ij}* be the daily precipitation amount on day

Let *RR _{ij}* be the daily precipitation amount on day

Let *RR _{ij}* be the daily precipitation amount on day

Let *RR _{ij}* be the daily precipitation amount on day

Let *RR _{wj}* be the daily precipitation amount on a wet day

Let *RR _{wj}* be the daily precipitation amount on a wet day

Let *RR _{ij}* be the daily precipitation amount on day

Annual count of `d` consecutive days where both `TX` < 5th percentile and `TN` < 5th percentile, where 10 ≥ d ≥ 2.

The number of individual heatwaves that occur each summer (Nov–Mar in southern hemisphere and May–Sep in northern hemisphere). A heatwave is defined as 3 or more days where either the EHF is positive, `TX` > 90th percentile of `TX` or where `TN` < 90th percentile of `TN`, where percentiles are calculated from base period specified by user.

See Perkins & Alexander (2013) for more details.

The number of days that contribute to heatwaves, as defined by HWN.

See Perkins & Alexander (2013) for more details.

The length of the longest heatwave identified by HWN.

See Perkins & Alexander (2013) for more details.

The mean temperature of all heatwaves identified by HWN.

See Perkins & Alexander (2013) for more details.

The peak daily value in the hottest heatwave (defined as the heatwave with the highest HWM.

See Perkins & Alexander (2013) for more details.

The number of individual 'coldwaves' that occur each year.

See Nairn & Fawcett (2013) for more details.

The number of days that contribute to 'coldwaves', as defined by CWN_ECF.

See Nairn & Fawcett (2013) for more details.

The length of the longest 'coldwave' identified by CWN_ECF.

See Nairn & Fawcett (2013) for more details.

The mean temperature of all 'coldwaves' identified by CWN_ECF.

See Nairn & Fawcett (2013) for more details.

The minimum daily value in the coldest heatwave (defined as the coldwave with the lowest EWM_ECF.

See Nairn & Fawcett (2013) for more details.

- Karl, T.R., N. Nicholls, and A. Ghazi. 1999.
, Weather and Climate Extremes, 42, 3-7. doi: 10.1007/978-94-015-9265-9_2**CLIVAR/GCOS/WMO workshop on indices and indicators for climate extremes: Workshop summary** - Peterson, T.C.,
*et al.*2001., WMO, Rep. WCDMP-47, WMO-TD 1071, Geneve, Switzerland, 143pp. Download (PDF from clivar.org): Peterson et al. 2001 (PDF)**Report on the Activities of the Working Group on Climate Change Detection and Related Rapporteurs 1998-2001** - Zhang, X.,
*et al.*2005., J. Climate, 18, 1641-1651. doi: 10.1175/JCLI3366.1**Avoiding Inhomogeneity in Percentile-Based Indices of Temperature Extremes**