Encoding of Drought indexes as defined by WMO

[sebvi]

Initial request

The WMO Handbook of Drought Indicators and Indices lists several indices which are not yet defined in the WMO GRIB2 table 4.2. This proposal suggests adding them together with additional entries in the tables 4.10, 4.101 and 4.102 to be used with the GRIB2 templates 4.105 to 4.107 and 4.112. These templates are designed to encode the reference period and processing of the data and we propose to extend these tables to be able to specify the underlying distribution used for the indices

Amendment details

Add a new entry in Code Table 4.1: Parameter category by product discipline

Code	Name
22	Drought indices

Create a new category "drought indices" in Code Table 4.2 under discipline 0 Product discipline 0 - Meteorological products, parameter category 22: drought indices

Parameter number	Parameter name	unit
0	Standardised Precipitation Index (SPI)	Numeric
1	Standardised Precipitation Evapotranspiration Index (SPEI)	Numeric
2	Standardised Streamflow Index (SFI)	Numeric
3	Standardised Reservoir Supply Index (SRSI)	Numeric
4	Standardised Water-level Index (SWI)	Numeric
5	Standardised Snowmelt and Rain Index (SMRI)	Numeric
6	Streamflow Drought Index (SDI)	Numeric

A description of these indices is available in the WMO Handbook of Drought Indicators and Indices, https://library.wmo.int/doc_num.php?explnum_id=3057.

ADD new entries in Code Table 4.10

Code number	name
102	Index processing

Note: For code number 102 the drought index encoded in the message is specified by the table entries from discipline 0 and parameter category 22 with the corresponding parameter number. The statistical processing period of the drought index is defined by the keys “length of time range” and "indicator of unit of time for the increment”.

ADD new entries in Code Table 4.101Type of relationship to reference dataset

Code number	name
23	Standardised drought index (see Note 5)
24-191	Reserved

Note 5: WMO proposed indices (https://library.wmo.int/doc_num.php?explnum_id=3057). The index is specified by setting discipline and parameter category / number to the specific index to be encoded. Drought indicators are calculated over different time ranges, prescribed by the keys lengthOfTimeRange and indicatorOfUnitForTimeRange in the templates 4.107, 4.108, 4.109 and 4.112. All standardised drought indices are calculated according to WMO guidelines of the SPI (https://library.wmo.int/doc_num.php?explnum_id=7768).

ADD new entries in Code Table 4.102 Statistical processing of reference period

Code number	Name
21	Index based on Normal distribution
22	Index based on Log-Normal distribution
23	Index based on Generalized Log-Normal distribution
24	Index based on Gamma distribution
25	Index based on Logistic distribution
26	Index based on Log-Logistic distribution
27	Index based on Generalized Logistic distribution
28	Index based on Weibull distribution
29	Index based on Generalized Extreme Value distribution
30	Index based on Pearson III distribution
31	Index based on empirical distribution
32-191	Reserved

Comments

https://community.wmo.int/en/activity-areas/agmp

Requestor(s)

Sebastien Villaume (ECMWF) Robert Osinski (ECMWF)

Stakeholder(s)

ECMWF

Publication(s)

Manual on Codes (WMO-No. 306), Volume I.2,

Expected impact of change

None

Collaborators

Jessica Keune (ECMWF)

References

Handbook of Drought Indicators and Indices (WMO-No. 1173)

Validation

No response

[amilan17]

https://github.com/wmo-im/CCT/wiki/20.to.22.September.2023 notes: Sebastien presented this at the meeting, it remains TBD...

[amilan17]

https://github.com/wmo-im/CCT/wiki/Teleconference.17.18.October.2023 notes: Proposal is still in progress; Sebastien talked about a simpler option of just creating a distinct code table (e.g. 4.10) and not try to create new templates; Sibylle noted that it could be generalized;

[amilan17]

https://github.com/wmo-im/CCT/wiki/Teleconference.17.18.October.2023 notes:

Sebastien introduced the proposal and team is invited to review; Sibylle recommends generalizing the proposal by removing "Drought" from name;

[sebvi]

I have updated the proposal to take into account @SibylleK 's suggestion. thank you

[amilan17]

https://github.com/wmo-im/CCT/wiki/Teleconference.21.22.November.2023 notes: Sebastien updated the branch; Will also remove "drought" from 4.10;

[sebvi]

removed "drought" from 4.10

[amilan17]

https://github.com/wmo-im/CCT/wiki/Teleconference.21.29.November.2023 notes:

ready

[amilan17]

https://github.com/wmo-im/CCT/wiki/Teleconference.10.January.2024 notes:

Anna requested some editorial changes;