A Prototype Precipitation Uncertainty Product for IMERG

The importance of quantifying precipitation uncertainties has gained widespread recognition with the increasing use of satellite precipitation products such as the Integrated Multi-satellitE retrievals for GPM (IMERG) from the Global Precipitation Measurement (GPM) mission. Despite this focus, progress on precipitation uncertainty has been limited due to challenges associated with its form, estimation, and use. In an effort to advance our understanding of precipitation uncertainty, this presentation outlines the creation of a prototype uncertainty product for IMERG.

The prototype uncertainty product is based on the censored shifted gamma distribution (CSGD) scheme, which provides parameters to create a probabilistic precipitation distribution for each 0.1° grid box at every ½ h globally. That is, instead of a single deterministic value for the precipitation rate, this uncertainty product provides a distribution from which quantiles, confidence intervals, or ensemble values can be generated. We describe its creation and characteristics, providing examples of how it can be interpreted and used, as well as an evaluation of the representativeness of the uncertainty distribution. We also demonstrate an application of this uncertainty product to estimate the range of precipitation accumulation over a region, highlighting the importance of accounting for spatiotemporal structure in the uncertainties.

We invite users interested in this prototype precipitation uncertainty product to download and explore the data and provide feedback, which might prove valuable for its continued improvement. Not only will this be an important step towards our eventual goal of including the uncertainties as part of the IMERG product, but we also hope to encourage further development of precipitation uncertainty schemes in general.