- Dataset Availability
- 1980-01-05T00:00:00Z–2024-10-31T06:00:00Z
- Dataset Provider
- University of California Merced
- Earth Engine Snippet
-
ee.ImageCollection("GRIDMET/DROUGHT") - Tags
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
4638.3 meters
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 |
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
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 with Earth Engine
Code Editor (JavaScript)
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');