Rainfall anomaly#

The objective of rainfall anomaly is to evaluate the quality of monthly rainfall over the country. This is achieved through analysis of anomalies, i.e. a comparison against a reference. The classic reference is the long-term average.

Rainfall anomaly is generated based on dekad data. The model will calculate the accumulated rainfall and other climate indices of precipitation based on that data during the most recent dekad which has been aggregated from pentad estimates. Every month has three dekads, such that the first two dekads have 10 days (i.e., 1-10, 11-20), and the third is comprised of the remaining days of the month (21-28 or 21-29 or 21-30 or 21-31. Therefore, the length of the third dekad of each month is not consistent and varies from 8-11 days, depending on the length of the month.

About the data

Characteristic

Description

Function

Displays dekad and monthly rainfall anomaly data

Variable

Rainfall anomaly

Geographic coverage

Global 50N-50S, 180W-180E

Spatial resolution

0.05 degree ~ 5.6 km at equator

Temporal resolution

dekad, 1-month, 3-month, 6-month, 9-month and 12-month, rolling by dekad.

Format

GeoTIFF

Unit

Percent (%) and milimeters

  • Ratio anomaly

    The anomaly is calculated based on percentage of the average.

    Anomaly (%) = 100 * rainfall/mean_rainfall

    where rainfall is current rainfall and mean_rainfall is long-term average of rainfall.

    Rainfall anomaly derived from CHIRPS data.

    Symbology

    The threshold and the symbology for the ratio anomaly can follow below colorcodes and image.

    Class

    Hex

    RGB

    20% and below

    #d73027 #d73027

    rgb(215,48,39)

    20 to 50%

    #f46d43 #f46d43

    rgb(244,109,67)

    50 to 70%

    #fdae61 #fdae61

    rgb(253,174,97)

    70 to 90%

    #fee090 #fee090

    rgb(254,224,144)

    90 to 110%

    #ffffbf #ffffbf

    rgb(255,255,191)

    110 to 130%

    #e0f3f8 #e0f3f8

    rgb(224,243,248)

    130 to 150%

    #abd9e9 #abd9e9

    rgb(171,217,233)

    150 to 180%

    #74add1 #74add1

    rgb(116,173,209)

    180% and above

    #4575b4 #4575b4

    rgb(69,117,180)

  • Difference anomaly

    The anomaly is calculated based on difference of the average.

    Anomaly (mm) = rainfall - mean_rainfall

    where rainfall is current rainfall and mean_rainfall is long-term average of rainfall.

    Difference anomaly derived from CHIRPS data.

Data access

Global rainfall anomaly data available at DEC S3: