# What is a climate index#

A climate index is a calculated value that can be used to describe the state and the changes in the climate system. The climate at a defined place is the average state of the atmosphere over a longer period of, for example, months or years. Changes on climate are much slower than on the weather, that can change strongly day by day.

Climate indices allow a statistical study of variations of the dependent climatological aspects, such as analysis and comparison of time series, means, extremes and trends.

Note

A good introduction for climate indices is on the website of the Integrated Climate Data Center (ICDC) of the University of Hamburg.

# icclim capabilities#

Currently, the climate indices as defined by European Climate Assessment & Dataset based on air temperature and precipitation variables can be computed with icclim:

11 cold indices (GD4, CFD, FD, HD17, ID, CSDI, TG10p, TN10p, TX10p, TXn, TNn)

1 drought indice (CDD)

9 heat indices (SU, TR, WSDI, TG90p, TN90p, TX90p, TXx, TNx, CSU)

14 rain indices (PRCPTOT, RR1, SDII, CWD, R10mm, R20mm, RX1day, RX5day, R75p, R75pTOT, R95p, R95pTOT, R99p, R99pTOT)

4 snow indices (SD, SD1, SD5cm, SD50cm)

6 temperature indices (TG, TN, TX, DTR, ETR, vDTR)

4 compound indices (CD, CW, WD, WW)

Detailed description of each indice is available at https://knmi-ecad-assets-prd.s3.amazonaws.com/documents/atbd.pdf. See table below for a short description of each indices. Most descriptions are extracted from clix-meta. Initially icclim was designed for online computing of climate indices through the climate4impact portal. In spite of existence of other packages able to compute climate indices (CDO, R package ), it was decided to develop a new software in Python. Python language was first of all chosen to interface with PyWPS: Python implementation of Web Processing Service (WPS) Standard. Another reason was to interface eventually with the OpenClimateGIS.

short name |
Description |
---|---|

TG |
Mean of daily mean temperature |

TN |
Mean of daily minimum temperature |

TX |
Mean of daily maximum temperature |

DTR |
Mean Diurnal Temperature Range |

ETR |
Intra-period extreme temperature range |

vDTR |
Mean day-to-day variation in Diurnal Temperature Range |

SU |
Number of Summer Days (Tmax > 25C) |

TR |
Number of Tropical Nights (Tmin > 20C) |

WSDI |
Warm-spell duration index |

TG90p |
Percentage of days when Tmean > 90th percentile |

TN90p |
Percentage of days when Tmin > 90th percentile |

TX90p |
Percentage of days when Tmax > 90th percentile |

TXx |
Maximum daily maximum temperature |

TNx |
Maximum daily minimum temperature |

CSU |
Maximum number of consecutive summer days (Tmax >25 C) |

GD4 |
Growing degree days (sum of Tmean > 4 C) |

FD |
Number of Frost Days (Tmin < 0C) |

CFD |
Maximum number of consecutive frost days (Tmin < 0 C) |

HD17 |
Heating degree days (sum of Tmean < 17 C) |

ID |
Number of sharp Ice Days (Tmax < 0C) |

TG10p |
Percentage of days when Tmean < 10th percentile |

TN10p |
Percentage of days when Tmin < 10th percentile |

TX10p |
Percentage of days when Tmax < 10th percentile |

TXn |
Minimum daily maximum temperature |

TNn |
Minimum daily minimum temperature |

CSDI |
Cold-spell duration index |

CDD |
Maximum consecutive dry days (Precip < 1mm) |

PRCPTOT |
Total precipitation during Wet Days |

RR1 |
Number of Wet Days (precip >= 1 mm) |

SDII |
Average precipitation during Wet Days (SDII) |

CWD |
Maximum consecutive wet days (Precip >= 1mm) |

R10mm |
Number of heavy precipitation days (Precip >=10mm) |

R20mm |
Number of very heavy precipitation days (Precip >= 20mm) |

RX1day |
Maximum 1-day precipitation |

RX5day |
Maximum 5-day precipitation |

R75p |
(in discussion) Days with RR > 75th percentile of daily amounts (wet days) |

R75pTOT |
(in discussion) Precipitation fraction due to very wet days (> 75th percentile) |

R95p |
(in discussion) Days with RR > 95th percentile of daily amounts (very wet days) |

R95pTOT |
(in discussion) Precipitation fraction due to very wet days (> 95th percentile) |

R99p |
(in discussion) Days with RR > 99th percentile of daily amounts (extremely wet days) |

R99pTOT |
(in discussion) Precipitation fraction due to very wet days (> 99th percentile) |

SD |
Mean of daily snow depth |

SD1 |
Snow days (SD >= 1 cm) |

SD5cm |
Number of days with snow depth >= 5 cm |

SD50cm |
Number of days with snow depth >= 50 cm |

CD |
Days with TG < 25th percentile of daily mean temperature and RR <25th percentile of daily precipitation sum |

CW |
Days with TG < 25th percentile of daily mean temperature and RR >75th percentile of daily precipitation sum |

WD |
Days with TG > 75th percentile of daily mean temperature and RR <25th percentile of daily precipitation sum |

WW |
Days with TG > 75th percentile of daily mean temperature and RR >75th percentile of daily precipitation sum |