1. Monthly maximum 1-day and consecutive 5-day precipitation
2. Simple precipitation intensity index
3. Annual count of days when precipitation is above a certain threshold
4. Maximum length of dry spell
5. Maximum length of wet spell
6. Annual total precipitation is above a certain threshold (percentiles)
7. Annual total precipitation in wet days

The total precipitation of a single day and of 5 days is determined.

For the monthly maximum 1-day precipitation (Rx1day): 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)

For the monthly maximum 5-day precipitation (Rx5day): 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)

The Simple precipitation intensity index (SDII) describes the mean daily precipitation amount during a time period.

Let RR_wj be the daily precipitation amount on wet days, where w(RR ≥ 1mm), in period j. If W is the number of wet days during period j, than:

SDII_j = ∑_^Ww=1(RR_wj)/W

The indices refer to a threshold X and the days on which it is exceeded. It indicates the annual number of days with at least X millimeter of precipitation.

Let RR_ij be the daily precipitation amount per day i during period j, and let X be the threshold of precipitation. Then count the number of days where:

RR_ij ≥ X mm

Typical thresholds X are 10 mm, and 20 mm. The corresponding indices are named R10mm and R20mm.

The maximum length of dry spell, which means consecutive dry days (CDD) is the longest period of consecutive days with no or less than 1 mm precipitation.

Let RR_ij be the daily precipitation amount per day i during time period j. Count the largest number of consecutive days where:

RR_ij < 1mm

The maximum length of wet spell, which means consecutive wet days (CWD) is the longest period of consecutive days with at least 1mm of precipitation.

Let RR_ij be the daily precipitation amount on day i during period j. Count the largest number of consecutive days where:

RR_ij ≥ 1mm

For this index, the annual total precipitation amount is determined and compared to the mean annual total precipitation amount of the climate base period. This index provides information about the deviation of a years precipitation from the long time mean.

Let RR_wj be the daily precipitation amount on a wet day w (RR ≥ 1mm) during time period i, and let RR_wnXX be the XX^th percentile of precipitation on wet days during the comparison period of climate base. Let W be the number of wet days during this period, then:

RXXp_j = ∑_^Ww=1(RR_wj) for all RR_wj > RR_wnXX

Typical values for the percentile XX of this index are 95 and 99. The corresponding indices are named R95pTOT and R99pTOT. A typical climate base time period is from the years 1961 to 1990.

This index describes the annual total precipitation in wet days (PRCPTOT).

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 = ∑_^Ji=1(RR_ij)

• http://cccma.seos.uvic.ca/ETCCDI/list_27_indices.shtml

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