CHC Early Estimates: Recent Rainfall and Seasonal Rainfall Monitors
The CHC Early Estimates provide a tool for monitoring rainfall conditions using combinations of CHIRPS, preliminary CHIRPS, and the CHIRPS-GEFS 15-day forecast. The Recent Rainfall Monitor provides near-real-time estimates of rainfall accumulations for the most recent pentad (5-6 days) to the most recent 18 pentads (3 months). The Seasonal Rainfall Monitor provides near-real-time estimates of rainfall accumulations for region-specific agricultural seasons ranging from 3 to 6 months.
The CHC Early Estimates products include rainfall totals (Total), difference from the 1981-2020 average (Anomaly), percent of average (% Average), standardized anomalies (SPI), historical rank for the 1st to 3rd wettest or driest (Rank), and the Seasonal Precipitation Performance Probability (SPPP). When mapping the latter four products—% Average, SPI, Rank, and SPPP—we apply a “dry mask,” in which areas that average less than 1mm per pentad during the given monitoring period are masked; the data files themselves are unmasked. Additionally, 1mm/pentad (max of 10 mm) is added to the numerator and denominator when calculating the percent of average in order to avoid extreme values in dry areas.
To-date rainfall values are based on preliminary CHIRPS data for the most recent pentads, and CHIRPS final data, when available. The outlook (+Forecast) combines these to-date accumulations with a rainfall forecast for the next three pentads (15-16 days) using CHIRPS-GEFS. CHC Early Estimates have the same latency as CHIRPS preliminary data, and are updated on the 2nd, 7th, 12th, 17th, 22nd, and 27th of each month, with the Seasonal Rainfall Monitor only being updated during the seasons of interest. As the Early Estimates include preliminary and forecast data, the information is subject to change. All products are back-processed when CHIRPS Final is made available in order to ensure the most accurate estimates. The latest year of Recent Rainfall Monitor graphics and products are available from the data portal, and only the most recent season of the Seasonal Rainfall Monitor graphics are available.
Recent Rainfall Data Access
The Recent Rainfall Monitor regional maps (pngs) can be accessed here. The left-side links lead to pngs showing to-date rainfall values. The “+Forecast” section links to the outlook, which includes the 3-pentad CHIRPS-GEFS forecast. The usage of preliminary or forecast data sources, and corresponding dates, are documented on the maps. Geotiffs of these products are available for download for the full CHIRPS extent (50N-50S, 180W-180E, 0.05° resolution). The geotiffs are not subset by region.
Seasonal Rainfall Data Access
In addition to the 5 products available in the Recent Rainfall set, the Seasonal Rainfall dataset also includes the Seasonal Precipitation Performance Probability (SPPP). The SPPP evaluates the probability that the current season’s precipitation total will finish in a given tercile corresponding to below-normal (< 33rd percentile), normal (33rd–66th percentile), and above-normal (> 66th percentile), relative to the historical distribution. Observed season totals for all previous years are used to generate the tercile boundaries for the season of interest. The current season's potential totals are calculated by taking to-date rainfall and running out the remainder of the season using all available previous years (n) of data (1981 to last year) to generate n potential season totals. Probabilities of each tercile are then calculated by counting the number of those scenarios that fall in each historical tercile and dividing by n. The SPPP maps the percent probability of the most likely tercile; i.e. if 29 of the 42 simulated season totals fall in the bottom tercile of historical totals, then the SPPP would be 69% probability that the current season will be ‘Below Normal.’
The latest regional maps for each season can be viewed on the CHC Early Estimates Seasonal Monitor page. Archived maps (pngs) and data (geotiffs) can be retrieved using the links below. The “with_forecast” subdirectories within the “png” and “tif” directories contain the +Forecast outlook maps and data mentioned above.
Middle East & North Africa Nov - Jul
Korea Apr - Oct