# Definitions of the core climate extreme indices

## There are 27 core climate extreme indices^{Footnote 1}

Index | Definition | Variable |
---|---|---|

Number of frost days (FD) | Annual count of days when daily minimum temperature is less than $0\xb0C$. Let TN Count the number of days where: TN |
minimum temperature |

Number of summer days (SU) | Annual count of days when daily maximum temperature is greater than $25\xb0C$. Let TX Count the number of days where: TX | maximum temperature |

Number of icing days (ID) | Annual count of days when daily maximum temperature is less than $0\xb0C$.
Let TX Count the number of days where: TX | maximum temperature |

Number of tropical nights (TR) | Annual count of days when daily minimum temperature is greater than $20\xb0C$. Let TN Count the number of days where: TN |
minimum temperature |

Growing season length (GSL) | Annual (January 1 to December 31 in Northern Hemisphere (NH), July 1 to June 30 in Southern Hemisphere (SH)) count between first span of at least 6 days with daily mean temperature greater than $5\xb0C$ and first span after July 1 (January 1 in SH) of 6 days with daily mean temperature less than $5\xb0C$. Let TG Count the number of days between the first occurrence of at least 6 consecutive days with: TG |
mean temperature |

Monthly maximum value of daily maximum temperature (TX_{x}) |
Let TX The maximum daily maximum temperature each month is then: TX |
maximum temperature |

Monthly maximum value of daily minimum temperature (TN_{x}) |
Let TN The maximum daily minimum temperature each month is then: TN |
maximum temperature |

Monthly minimum value of daily maximum temperature (TX_{n}) |
Let TX The minimum daily maximum temperature each month is then: TX |
minimum temperature |

Monthly minimum value of daily minimum temperature (TN_{n}) |
Let TN The minimum daily minimum temperature each month is then: TN |
minimum temperature |

Percentage of days when daily minimum temperature is less than the 10^{th} percentile (TN10p) |
Let TN The percentage of time for the base period is determined where: TN To avoid possible inhomogeneity across the in-base and out-base periods, the calculation for the base period (1961-1990) requires the use of a bootstrap procedure. Details are described in Zhang et al. (2005). |
minimum temperature |

Percentage of days when daily maximum temperature is less than the 10^{th} percentile (TX10p) |
Let TX The percentage of time for the base period is determined where: TX To avoid possible inhomogeneity across the in-base and out-base periods, the calculation for the base period (1961-1990) requires the use of a bootstrap procedure. Details are described in Zhang et al. (2005). |
maximum temperature |

Percentage of days when daily minimum temperature is greater than the 90^{th} percentile (TN90p) |
Let TN The percentage of time for the base period is determined where: TN To avoid possible inhomogeneity across the in-base and out-base periods, the calculation for the base period (1961-1990) requires the use of a bootstrap processure. Details are described in Zhang et al. (2005). |
minimum temperature |

Percentage of days when daily maximum temperature is greater than the 90^{th} percentile (TX90p) |
Let TX The percentage of time for the base period is determined where: TX To avoid possible inhomogeneity across the in-base and out-base periods, the calculation for the base period (1961-1990) requires the use of a bootstrap processure. Details are described in Zhang et al. (2005). |
maximum temperature |

Warm spell duration index (WSDI) | Annual count of days with at least 6 consecutive days when daily maximum temperature is greater than the 90 Let TX Then the number of days per period is summed where, in intervals of at least 6 consecutive days: TX |
maximum temperature |

Cold spell duration index (CSDI) | Annual count of days with at least 6 consecutive days
when daily minimum temperature is less than the 10 Let TN Then the number of days per period is summed where, in intervals of at least 6 consecutive days: TN |
minimum temperature |

Daily temperature range (DTR) | Monthly mean difference between daily maximum and minimum temperature Let TX If I represents the number of days in j, then:
DTR |
minimum temperature maximum temperature |

Monthly maximum 1-day precipitation (Rx1day) | Let RR The maximum 1-day value for period j are: Rx1day |
precipitation |

Monthly maximum consecutive 5-day precipitation (Rx5day) | Let RR Then maximum 5-day values for period j are: Rx5day |
precipitation |

Annual count of days when precipitation is greater than or equal to 10mm (R10mm) | Let RR Count the number of days where: RR |
precipitation |

Simple precipitation intensity index (SDII) | Let RR If W represents number of wet days in j, then: $\mathrm{SDIIj}=\frac{\sum _{w=1}^{W}\mathrm{RRwj}}{W}$ |
precipitation |

Annual count of days when precipitation is greater than or equal to 20mm (R20mm) | Let RR Count the number of days where: RR |
precipitation |

Annual count of days when precipitation is greater than or equal to "nnmm", nn is a user defined threshold (Rnnmm) | Let RR Count the number of days where: RR |
precipitation |

Maximum length of dry spell, maximum number of consecutive days with daily precipitation less than 1mm (CDD) | Let RR Count the largest number of consecutive days where: RR |
precipitation |

Maximum length of wet spell, maximum number of consecutive days with daily precipitation greater than or equal to 1mm (CWD) | Let RR Count the largest number of consecutive days where: RR |
precipitation |

Annual total precipitation when daily precipitation is greater than the 95^{th} percentile (R95pTOT) |
Let RR If W represents the number of wet days in the period, then:
R95p |
precipitation |

Annual total precipitation when daily precipitation is greater than the 99^{th} percentile (R99pTOT) |
Let RR If W represents the number of wet days in the period, then:
R99p |
precipitation |

Annual total precipitation in wet days (PRCPTOT) | Annual total precipitation in wet days: Let RR If I represents the number of days in j , then:
PRCPTOT |
precipitation |