This website provides information about how effective several drought indices and indicators are across North America. The information is derived from a collaborative project in 2019-2020 funded and managed by the North America Commission for Environmental Cooperation (CEC). The CEC project engaged drought users and stakeholders across North America through a series of surveys and virtual meetings to assess how drought indices and indicators were used in the diverse climates of the continent. Members of the project's steering committee included participants from U.S., Canadian, and Mexican government agencies, academic institutions, and other organizations involved in drought monitoring. The data were compiled by a contractor managed by the CEC. The drought indices and indicators that were evaluated include those listed in the World Meteorological Organization (WMO) Handbook of Drought Indicators and Indices as well as others not listed in the WMO Handbook. The project specified that NOAA's National Centers for Environmental Information (NCEI) would manage this web site and that the information would be made available in all three languages of North America – English, Spanish, and French.

The CEC project and WMO Handbook only identified drought indices and indicators that are used for monitoring drought; they did not provide an assessment or recommendations on which indicators and indices are most appropriate to use. A subsequent journal article reviewed user engagement workshops and the published peer-reviewed literature to provide an assessment and recommendations on which indicators and indices are appropriate for monitoring drought in the diverse climates of North America. The journal article can be accessed here: https://www.mdpi.com/2073-4433/14/12/1794

The data are displayed in a series of tables chosen by the reader. For some tables, the reader selects from pulldown menus what data are displayed and how the data are displayed.

The Koeppen climate classification system is one of the oldest and best known climate classification systems. The Koeppen climate zones were used in this study to identify the diverse regions of North America. The area of responsibility of a respondent may include multiple climate zones.
Beck et al. (2018)
WMO & GWP (2016)
Critchfield (1974)

The following Koeppen climate zones were identified in this study:

Af
Tropical Rainforest
Am
Tropical Monsoon
Aw
Tropical Savanna (Wet and Dry Climate)
BW
Arid (desert)
BWh
Hot Desert Climate
BWk
Cold Desert Climate
BS
Semi-Arid
BSh
Hot Semi-Arid Climate
BSk
Cold Semi-Arid Climate
Cs
Mediterranean
Csa
Hot-Summer Mediterranean Climate
Csb
Warm-Summer Mediterranean Climate
Cw
Temperate with dry winters
Cwa
Warm Oceanic Climate / Humid Subtropical Climate
Cwb
Subtropical highland climate or temperate oceanic climate with dry winters
Cwc
Cold subtropical highland/Subpolar Oceanic
Cf
Humid subtropical
Cfa
Humid Subtropical Climate
Cfb
Temperate Oceanic Climate
Cfc
Subpolar Oceanic Climate
Dsa
Humid Continental Climate - Dry Warm Summer
Dsb
Humid Continental Climate - Dry Cool Summer
Dsc
Continental Subarctic - Cold Dry Summer
Dsd
Continental Subarctic - Dry Summer, Very Cold Winter
Dwa
Humid Continental Hot Summers With Dry Winters
Dwb
Humid Continental Mild Summer With Dry Winters
Dwc
Subarctic With Cool Summers And Dry Winters
Dwd
Subarctic With Cold Winters And Dry Winters
Dfa
Humid Continental Hot Summers With Year-round Precipitation
Dfb
Humid Continental Mild Summer, Wet All Year
Dfc
Subarctic With Cool Summers And Year-round Precipitation
Dfd
Subarctic With Cold Winters And Year-round Precipitation
ET
Tundra Climate
EF
Ice Cap Climate

  • Beck, H. E., Zimmermann, N. E., McVicar, T. R., Vergopolan, N., Berg, A., & Wood, E. F. (2018). Present and future Köppen-Geiger climate classification maps at 1-km resolution. Scientific data, 5, 180214. https://doi.org/10.1038/sdata.2018.214.
  • Critchfield, H. J. (1974). General Climatology, Third Edition. Prentice-Hall, Inc. Englewood Cliffs.
  • WMO & GWP. (2016). Handbook of Drought Indicators and Indices (M. Svoboda and B.A. Fuchs). Integrated Drought Management Programme (IDMP), Integrated Drought Management Tools and Guidelines Series 2. Geneva.
  • Heim, R.R., Jr.; Bathke, D.; Bonsal, B.; Cooper, E.W.T.; Hadwen, T.; Kodama, K.; McEvoy, D.; Muth, M.; Nielsen-Gammon, J.W.; Prendeville, H.R.; et al. A Review of User Perceptions of Drought Indices and Indicators Used in the Diverse Climates of North America. Atmosphere 2023, 14, 1794. https://doi.org/10.3390/atmos14121794

Each drought index or drought indicator was rated by the respondents as to its effectiveness in their climate zone(s). The ratings ranged from less effective (1) to very effective (5). The indices and indicators in the WMO Handbook were rated for short-term drought and long-term drought. There was no distinction made between short-term and long-term drought for indices that were not in the WMO Handbook. The tables display the percentage of respondents who gave the indices each rating (1-5).

Type of Drought Index

  • Composite or Modeled
  • Hydrology
  • Meteorology
  • Remote Sensing
  • Soil Moisture
  • Not in WMO Handbook

Drought Index

  • 30-day forecasts
  • 5-day forecasts
  • 8 to 14-day forecasts
  • Aggregate Dryness Index (ADI)
  • Agricultural Reference Index for Drought (ARID)
  • Aridity Anomaly Index (AAI)
  • Aridity Index (AI)
  • China Z Index (CZI)
  • Combined Drought Indicator (CDI)
  • Crop Moisture Index (CMI)
  • Crop status
  • Crop-specific Drought Index (CSDI)
  • Deciles
  • Drought Area Index (DAI)
  • Drought Reconnaissance Index (DRI)
  • Effective Drought Index (EDI)
  • Enhanced Vegetation Index (EVI)
  • Evaporative Stress Index (ESI)
  • Evapotranspiration Deficit Index (ETDI)
  • Global Integrated Drought Monitoring and Prediction System (GIDMaPS)
  • Global Land Data Assimilation System (GLDAS)
  • Groundwater depth
  • Hydro-thermal Coefficient of Selyaninov (HTC)
  • Keetch–Byram Drought Index (KBDI)
  • Local burn bans
  • Media reports
  • Multivariate Standardized Drought Index (MSDI)
  • NOAA Drought Index (NDI)
  • Normalized Difference Vegetation Index (NDVI)
  • Normalized Difference Water Index (NDWI) & Land Surface Water Index (LSWI)
  • Other
  • Palmer Drought Severity Index (PDSI)
  • Palmer Hydrological Drought Index (PHDI)
  • Palmer Z Index
  • Percent of Normal Precipitation
  • Precipitation departures from normal
  • Precipitation percentiles
  • Precipitation ranks
  • Rainfall Anomaly Index (RAI)
  • Reclamation Drought Index (RDI)
  • Reported drought impacts
  • Reservoir storage
  • Seasonal forecasts
  • Self-Calibrated Palmer Drought Severity Index (sc-PDSI)
  • Soil Adjusted Vegetation Index (SAVI)
  • Soil moisture
  • Soil Moisture Anomaly (SMA)
  • Soil Moisture Deficit Index (SMDI)
  • Soil Water Storage (SWS)
  • Standardized Anomaly Index (SAI)
  • Standardized Precipitation Evapotranspiration Index (SPEI)
  • Standardized Precipitation Index (SPI)
  • Standardized Reservoir Supply Index (SRSI)
  • Standardized Snowmelt and Rain Index (SMRI)
  • Standardized Streamflow Index (SSFI)
  • Standardized Water-level Index (SWI)
  • Streamflow
  • Streamflow Drought Index (SDI)
  • Surface Water Supply Index (SWSI)
  • Temperature Condition Index (TCI)
  • Temperature departures from normal
  • Temperature ranks
  • U.S. Drought Outlook
  • United States Drought Monitor (USDM)
  • Vegetation Condition Index (VCI)
  • Vegetation Drought Response Index (VegDRI)
  • Vegetation greenness
  • Vegetation Health Index (VHI)
  • Water quality
  • Water Requirement Satisfaction Index (WRSI & Geo-spatial WRSI)
  • Water use (demand)
  • Weighted Anomaly Standardized Precipitation (WASP)
  • Wildfire locations / reports

The respondents identified the factors which affected their choice of drought indices and indicators used in their region/area of responsibility. The table displays the percent of respondents identifying each factor for each climate zone. The factors included:

  • Availability of relevant and required data to calculate the index or indicator
  • Complexity or difficulty of the required calculation
  • Relevance of the index or indicator to my area/region
  • My familiarity with the specific index or indicator
  • The history of indices and/or indicators used previously in my area/region
  • Other (an unspecified factor that is not listed above)

The respondents identified the economic or environmental or social impact of drought as being important for their region/area. The table displays the percent of respondents identifying each impact for each climate zone. The impacts included:

  1. economic impacts/increased costs
    • increased farming costs (for accessing water such as irrigation or drilling new wells)
    • increased ranching costs (for animal feed and water)
    • increased customer costs (hydroelectric power costs)
    • increased business costs (businesses that supply water to customers)
    • increased transportation costs
    • increased food costs
  2. economic impacts/reduced capacity or income
    • crop destruction
    • decline in farming & ranching income
    • decline in timber industry income
    • decline in recreational income
    • reservoir management
    • nuclear power plants
  3. environmental impacts/habitat loss
    • loss or destruction of fish & wildlife habitat
    • lower water levels in reservoirs lakes & ponds
    • loss of wetlands
    • loss of or die back of forests
    • more wildfires
    • wind and water erosion of soils
  4. environmental impacts/habitat degradation
    • lack of food & water for wildlife
    • increased wildlife disease due to reduced food & water
    • migration of wildlife
    • increased stress on endangered or threatened species
    • reduced soil quality
  5. social impacts
    • anxiety &/or depression
    • health problems (water)
    • health problems (dust)
    • loss of human life
    • threat of forest & range fires
    • reduced incomes
    • human migration
    • reduced recreation

The respondents indicated how important each of the five drought types were in their region/area. The table displays the percent of respondents identifying each drought type as important for each climate zone. The five drought types are:

  • Agricultural (when crops become affected)
  • Ecological (when terrestrial and aquatic ecosystems are impacted)
  • Hydrological (when low water levels become evident in streams, reservoir and groundwater)
  • Meteorological (when dry weather patterns dominate an area)
  • Socioeconomic (when the supply and demand of commodities are impacted)

The performance of the indices across the four seasons and geographically was assessed by climate zone.

The typical drought duration, and how often drought has occurred in the last ten years, were assessed by climate zone.