The Global Climate Observing System international collaboration has identified 50 Essential Climate Variables (ECVs) comprising
Atmospheric (over land sea and ice)
Oceanic
Terrestrial
All ECVs are technically and economically feasible for systematic observation. It is these variables for which international exchange is required for both current and historical observations.
Climate variables are also described on the Bureau of Meteorology website here .
Extreme climate indices are defined by, and are available for some global climate models from ClimDEX , a project that produces a suite of in situ and gridded land-based global datasets of indices representing the more extreme aspects of climate. These are defined as follows:
Code |
Description |
Definition |
---|---|---|
FD |
Number of frost days |
Annual count of days when daily minimum temperature < 0^{o}C. |
SU |
Number of summer days |
Annual count of days when TX (daily maximum temperature) > 25^{o}C. |
ID |
Number of icing days |
Annual count of days when TX (daily maximum temperature) < 0^{o}C. |
TR |
Number of tropical nights |
Annual count of days when TN (daily minimum temperature) > 20^{o}C. |
GSL |
Growing season length |
Annual (1^{st} Jan to 31^{st} Dec in Northern Hemisphere (NH), 1^{st} July to 30^{th} June in Southern Hemisphere (SH)) count between first span of at least 6 days with daily mean temperature TG>5^{o}C and first span after July 1^{st} (Jan 1^{st} in SH) of 6 days with TG<5^{o}C. |
TX_{x} |
Monthly maximum value of daily maximum temperature |
Let TX_{x} be the daily maximum temperatures in month k, period j. The maximum daily maximum temperature each month is then: TX_{xkj}=max(TX_{xkj}) |
TN_{x} |
Monthly maximum value of daily minimum temperature |
Let TN_{x} be the daily minimum temperatures in month k, period j. The maximum daily minimum temperature each month is then: TN_{xkj}=max(TN_{xkj}) |
TX_{n} |
Monthly minimum value of daily maximum temperature |
Let TX_{n} be the daily maximum temperatures in month k, period j. The minimum daily maximum temperature each month is then: TX_{nkj}=min(TX_{nkj}) |
TN_{n} |
Monthly minimum value of daily minimum temperature |
Let TN_{n} be the daily minimum temperatures in month k, period j. The minimum daily minimum temperature each month is then: TN_{nkj}=min(TN_{nkj}) |
TN10p |
Percentage of days when TN < 10^{th} percentile |
Let TN_{ij} be the daily minimum temperature on day i in period j and let TN_{in}10 be the calendar day 10^{th} percentile centred on a 5-day window for the base period 1961-1990. The percentage of time for the base period is determined where: TN_{ij} < TN_{in}10 |
TX10p |
Percentage of days when TX < 10^{th} percentile |
Let TX_{ij} be the daily maximum temperature on day i in period j and let TX_{in}10 be the calendar day 10^{th} percentile centred on a 5-day window for the base period 1961-1990. The percentage of time for the base period is determined where: TX_{ij} < TX_{in}10 |
TN90p |
Percentage of days when TN > 90^{th} percentile |
Let TN_{ij} be the daily minimum temperature on day i in period j and let TN_{in}90 be the calendar day 90^{th} percentile centred on a 5-day window for the base period 1961-1990. The percentage of time for the base period is determined where: TN_{ij} > TN_{in}90 |
TX90p |
Percentage of days when TX > 90^{th} percentile |
Let TX_{ij} be the daily maximum temperature on day i in period j and let TX_{in}90 be the calendar day 90^{th} percentile centred on a 5-day window for the base period 1961-1990. The percentage of time for the base period is determined where: TX_{ij} > TX_{in}90 |
WSDI |
Warm spell duration index |
Annual count of days with at least 6 consecutive days when TX > 90^{th} percentile |
CSDI |
Cold spell duration index |
Annual count of days with at least 6 consecutive days when TN < 10^{th} percentile |
DTR |
Daily temperature range |
Monthly mean difference between TX and TN |
Rx1day |
Monthly maximum 1-day precipitation |
Let RR_{ij} be the daily precipitation amount on day i in period j. The maximum 1-day value for period j are: Rx1day_{j} = max (RR_{ij}) |
Rx5day |
Monthly maximum consecutive 5-day precipitation |
Let RR_{kj} be the precipitation amount for the 5-day interval ending _{k}, period j. Then maximum 5-day values for period j are: Rx5day_{j} = max (RR_{kj}) |
SDII |
Simple precipitation intensity index |
Let RR_{wj} be the daily precipitation amount on wet days, w (RR ≥ 1mm) in period j. If W represents number of wet days in j, then: $$SDII_{j}={∑↙{w=1}↖W RR_{wj}}/W$$ |
R10mm |
Annual count of days when PRCP≥ 10mm |
Let RR_{ij} be the daily precipitation amount on day i in period j. Count the number of days where: RR_{ij} ≥ 10mm |
R20mm |
Annual count of days when PRCP≥ 20mm |
Let RR_{ij} be the daily precipitation amount on day i in period j. Count the number of days where: RR_{ij} ≥ 20mm |
Rnnmm |
Annual count of days when PRCP≥ nnmm, nn is a user defined threshold |
Let RR_{ij} be the daily precipitation amount on day i in period j. Count the number of days where: RR_{ij} ≥ nnmm |
CDD |
Maximum length of dry spell, maximum number of consecutive days with RR < 1mm |
Let RR_{ij} be the daily precipitation amount on day i in period j. Count the largest number of consecutive days where: RR_{ij} < 1mm |
CWD |
Maximum length of wet spell, maximum number of consecutive days with RR ≥ 1mm |
Let RR_{ij} be the daily precipitation amount on day i in period j. Count the largest number of consecutive days where: RR_{ij} ≥ 1mm |
R95pTOT |
Annual total PRCP when RR > 95p |
Let RR_{wj} be the daily precipitation amount on a wet day w (RR ≥ 1.0mm) in period i and let RR_{wn}95 be the 95^{th} percentile of precipitation on wet days in the 1961-1990 period. If W represents the number of wet days in the period, then: $R95p_{j}=∑↙{w=1}↖W RR_{wj}$ where $RR_{wj} > RR_{wn}95$ |
R99pTOT |
Annual total PRCP when RR > 99p |
Let RR_{wj} be the daily precipitation amount on a wet day w (RR ≥ 1.0mm) in period i and let RR_{wn}99 be the 99^{th} percentile of precipitation on wet days in the 1961-1990 period. If W represents the number of wet days in the period, then: $R99p_{j}=∑↙{w=1}↖W RR_{wj}$ where $RR_{wj} > RR_{wn}99$ |
PRCPTOT |
Annual total precipitation in wet days |
Let RR_{ij} be the daily precipitation amount on day i in period j. If I represents the number of days in j, then $$PRCPTOT_{j}=∑↙{i=1}↖{I} RR_{ij}$$ |