Climate Exchange

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The USDM is used for the US drought depiction. It is produced on a

weekly basis by NOAA, USDA and NDMC partners from a large suite

of in situ and satellite-based objective drought indicators (includ-

ing the Standardized Precipitation Index (SPI), Palmer Drought

Index, streamflow, mountain snow pack, precipitation percentiles,

modelled soil moisture, Vegetation Drought Response Index and

many others), impacts information (such as reduced agricultural

production), and local field input from over 300 participants. The

indices and indicators are combined using a simple D0-D4 scheme

and a percentile ranking methodology to address both short-term

and long-term drought. The USDM undergoes a peer-review process

through an e-mail based discussion list each week during its prepa-

ration, to ensure that the weekly drought depiction represents the

best ‘blended convergence of evidence’.

The weekly USDM map

from the week closest to the end of the month is used for the US

depiction on the NADM map for that month. The national Drought

Monitors (DMs) for Canada (by AAFC) and Mexico (by SMN) are

prepared in a similar manner.

Each of the three countries provides daily and/or monthly temper-

ature and precipitation data to the NCDC for the computation of

monthly station and climate division-based continental drought

indices (SPI, Palmer Drought Index, and percentage of long-term

average precipitation). These continental drought indices, computed

using the same methodology and calibration periods, are used by

the lead author in conjunction with other drought indicators with

North American coverage (such as the NOAA satellite-derived

Vegetative Health Index and continental scale modelled soil mois-

ture), as guidance to prepare a consistent NADM drought depiction

along the international borders. The NADM continental

map and narrative are provided to the partner agen-

cies and organizations for an iterative peer review. The

NADM map is finalized, generally, by the tenth day of

the month and put online by the NCDC by the elev-

enth and the NADM narrative is placed online a few

days later. The NADM map GIS shape files are available

online (restricted access), and the NADM is available

at no cost on both a static website

and via the NIDIS

drought portal.

Both the NADM map and narrative

are provided in the languages of the three countries

(English, French and Spanish). The continental drought

indicators are also available at the website in both map

format and ASCII data files.

Policy decisions are made at the top management level

of the partner agencies and organizations and are guided

by bilateral and trilateral agreements. Operational,

technical, administrative, scientific and user issues are

addressed and evaluated at biennial NADM Forumwork-

shops hosted, on a rotating basis, by the three countries.

These workshops provide a mechanism for valuable

feedback, whereby users may express their drought

monitoring needs to the NADM authors (resulting in

improvements to the NADM product) and receive guid-

ance on the appropriate use and interpretation of the

NADM. Common user concerns expressed at NADM and

USDM forums include appropriate ways to use the DM

products and indices in their decision-making processes,

The flow of production of the NADM

Source: NOAA