GRIDMET DROUGHT: CONUS drought indices

GRIDMET/DROUGHT
Dataset Availability
1980-01-05T00:00:00 - 2020-11-05T00:00:00
Dataset Provider
Earth Engine Snippet
ee.ImageCollection("GRIDMET/DROUGHT")
Tags
drought conus crop palmer geophysical climate gridmet metdata precipitation evapotranspiration climatic-water-balance spi spei eddi pdsi z merced

Description

This dataset contains drought indices derived from the 4-km daily Gridded Surface Meteorological (GRIDMET) dataset. The drought indices provided include the standardized precipitation index (SPI), the evaporative drought demand index (EDDI), the standardized precipitation evapotranspiration index (SPEI), the Palmer Drought Severity Index (PDSI) and Palmer Z Index (Z).

SPI, EDDI, and SPEI are supplied on different time scales corresponding to the time aggregation of precipitation, reference evapotranspiration, and precipitation minus reference evapotranspiration, respectively. The time scales include 14 day, 30 day, 90 day, 180 day, 270 day, 1 year, 2 years and 5 years. The standardization is done by using a non-parametric standardized probability based method where plotting positions are used to obtain probabilities which are transformed to indices assuming an inverse-normal distribution. All data are standardized over a common time period of 1981-2016.

PDSI and Z are calculated using a modified version of the Palmer formula which uses reference evapotranspiration and precipitation from GRIDMET, and a static soil water holding capacity layer (top 1500mm) from STATSGO. Modifications to the coefficients of the original Palmer formula are applied to calculate PDSI. The baseline period for PDSI and Z calculations is 1979-2018.

Interpretation of the drought indices in this dataset is different for PDSI and Z than for SPI, SPEI and EDDI. Utilizing the interpretation from the US Drought monitor, values of these drought indices have the following meaning:

PDSI and z:

  • 5.0 or more (extremely wet)
  • 4.0 to 4.99 (very wet)
  • 3.0 to 3.99 (moderately wet),
  • 2.0 to 2.99 (slightly wet)
  • 1.0 to 1.99 (incipient wet spell)
  • -0.99 to 0.99(near normal)
  • -1.99 to -1.00 (incipient dry spell)
  • -2.99 to -2.00 (mild drought)
  • -3.99 to -3.00 (moderate drought)
  • -4.99 to -4.00 (severe drought)
  • -5.0 or less (extreme drought)

SPI/SPEI/EDDI:

  • 2.0 or more (extremely wet)
  • 1.6 to 1.99 (very wet)
  • 1.3 to 1.59 (moderately wet),
  • 0.8 to 1.29 (slightly wet)
  • 0.5 to 0.79 (incipient wet spell)
  • -0.49 to 0.49(near normal),
  • -0.79 to -0.5 (incipient dry spell)
  • -1.29 to -0.8 (mild drought)
  • -1.59 to -1.3 (moderate drought)
  • -1.99 to -1.6 (severe drought)
  • -2.0 or less (extreme drought).

This dataset contains provisional products that are replaced with updated versions when the complete source data become available. Products can be distinguished by the value of the 'status' property. At first, assets are ingested with status='early'. After several days, they are replaced by assets with status='provisional'. After about 2 months, they are replaced by the final assets with status='permanent'.

Bands

Resolution
2.5 arc minutes

Bands

Name Min Max Description
spi14d -6* 6*

Standardized Precipitation Index (SPI) where precipitation was aggregated for the last 14 days

spi30d -6* 6*

Standardized Precipitation Index (SPI) where precipitation was aggregated for the last 30 days

spi90d -6* 6*

Standardized Precipitation Index (SPI) where precipitation was aggregated for the last 90 days

spi180d -6* 6*

Standardized Precipitation Index (SPI) where precipitation was aggregated for the last 180 days

spi270d -6* 6*

Standardized Precipitation Index (SPI) where precipitation was aggregated for the last 270 days

spi1y -6* 6*

Standardized Precipitation Index (SPI) where precipitation was aggregated for the last 1 year

spi2y -6* 6*

Standardized Precipitation Index (SPI) where precipitation was aggregated for the last 2 years

spi5y -6* 6*

Standardized Precipitation Index (SPI) where precipitation was aggregated for the last 5 years

eddi14d -6* 6*

Evaporative Drought Demand Index (EDDI) where potential evapotranspiration was aggregated for the last 14 days

eddi30d -6* 6*

Evaporative Drought Demand Index (EDDI) where potential evapotranspiration was aggregated for the last 30 days

eddi90d -6* 6*

Evaporative Drought Demand Index (EDDI) where potential evapotranspiration was aggregated for the last 90 days

eddi180d -6* 6*

Evaporative Drought Demand Index (EDDI) where potential evapotranspiration was aggregated for the last 180 days

eddi270d -6* 6*

Evaporative Drought Demand Index (EDDI) where potential evapotranspiration was aggregated for the last 270 days

eddi1y -6* 6*

Evaporative Drought Demand Index (EDDI) where potential evapotranspiration was aggregated for the last 1 year

eddi2y -6* 6*

Evaporative Drought Demand Index (EDDI) where potential evapotranspiration was aggregated for the last 2 years

eddi5y -6* 6*

Evaporative Drought Demand Index (EDDI) where potential evapotranspiration was aggregated for the last 5 years

spei14d -6* 6*

Standardized Precipitation Evapotranspiration Index (SPEI) where climatic water balance was aggregated for the last 14 days

spei30d -6* 6*

Standardized Precipitation Evapotranspiration Index (SPEI) where climatic water balance was aggregated for the last 30 days

spei90d -6* 6*

Standardized Precipitation Evapotranspiration Index (SPEI) where climatic water balance was aggregated for the last 90 days

spei180d -6* 6*

Standardized Precipitation Evapotranspiration Index (SPEI) where climatic water balance was aggregated for the last 180 days

spei270d -6* 6*

Standardized Precipitation Evapotranspiration Index (SPEI) where climatic water balance was aggregated for the last 270 days

spei1y -6* 6*

Standardized Precipitation Evapotranspiration Index (SPEI) where climatic water balance was aggregated for the last 1 year

spei2y -6* 6*

Standardized Precipitation Evapotranspiration Index (SPEI) where climatic water balance was aggregated for the last 2 years

spei5y -6* 6*

Standardized Precipitation Evapotranspiration Index (SPEI) where climatic water balance was aggregated for the last 5 years

pdsi -15* 15*

Palmer Drought Severity Index

z -15* 15*

Palmer Z Index

* estimated min or max value

Image Properties

Image Properties

Name Type Description
status STRING

'early', 'provisional', or 'permanent'

Terms of Use

Terms of Use

This work (METDATA, by John Abatzoglou) is in the public domain and is free of known copyright restrictions. Users should properly cite the source used in the creation of any reports and publications resulting from the use of this dataset and note the date when the data was acquired.

Citations

Citations:
  • Abatzoglou J. T., Development of gridded surface meteorological data for ecological applications and modelling, International Journal of Climatology. (2012) doi:10.1002/joc.3413

Explore in Earth Engine

var collection = ee.ImageCollection('GRIDMET/DROUGHT');
print(collection);

// Filter by date
var dS = '2020-03-30';
var dE = '2020-03-30';
var dSUTC = ee.Date(dS, 'GMT');
var dEUTC = ee.Date(dE, 'GMT');
var filtered = collection.filterDate(dSUTC, dEUTC.advance(1, 'day'));
print(collection.aggregate_array('system:index'));

// Select variables pdsi and z
var PDSI = filtered.select('pdsi');
var Z = filtered.select('z');

// Select variables for SPI/SPEI/EDDI
// Note that possible timescales for SPI/SPEI/EDDI are:
// 14d (14 day), 30d (30 day), 90d (90 day), 180d (180 day),
// 1y (1 year), 2y (2 year), 5y (5 year)
// Here we choose 2years = 48 months
var SPI2y = filtered.select('spi2y');
var SPEI2y = filtered.select('spei2y');
var EDDI2y = filtered.select('spei2y');

// Make a color palette that is similar to USDM drought classification
var usdmColors = "0000aa,0000ff,00aaff,00ffff,aaff55,ffffff,ffff00,fcd37f,ffaa00,e60000,730000";

// Make color options for standardized variables spi/spei/eddi
var minColorbar= -2.5;
var maxColorbar= 2.5;
var colorbarOptions1 = {
  'min':minColorbar,
  'max':maxColorbar,
  'palette': usdmColors
};

// Make color options for Palmer variables psdi/z
var minColorbar= -6;
var maxColorbar= 6;
var colorbarOptions2 = {
  'min':minColorbar,
  'max':maxColorbar,
  'palette': usdmColors
};

// Add map layers to Google Map
Map.addLayer(ee.Image(PDSI.first()), colorbarOptions2, 'PDSI');
Map.addLayer(ee.Image(Z.first()), colorbarOptions2, 'Palmer-Z');
Map.addLayer(ee.Image(SPI2y.first()), colorbarOptions1, 'SPI-48months');
Map.addLayer(ee.Image(SPEI2y.first()), colorbarOptions1, 'SPEI-48months');
Map.addLayer(ee.Image(EDDI2y.first()), colorbarOptions1, 'EDDI-48months');