The evaluation and downscaling‐calibration of IMERG precipitation products at sub‐daily scales over a metropolitan region

Abstract

The Global Precipitation Measurement (GPM) Integrated Multi‐satellitE Retrievals for GPM products (i.e., IMERG) provide new‐generation satellite precipitation measurements. For urban contexts, however, the issues of its bias and insufficient resolutions still exist. This study aims to develop high‐precision and high‐resolution (e.g., 0.01°/1 h) data for a metropolitan region based on IMERG and gauge precipitations. The original IMERG product is evaluated using hourly in situ precipitations from 47 gauges. A spatial downscaling‐calibration (DC) technique is then developed to enhance the IMERG using the Normalized Difference Vegetation Index. The results show the limited capability of IMERG to capture sub‐daily precipitation and high‐intensity precipitation. The proposed DC method significantly improves IMERG performance, with correlation coefficient (CC) increasing from 0.07 to 0.75, and probability of detection improving from 0.34 to 0.90 at the hourly scale. In terms of spatial rainfall distribution, 86% of mean absolute error and 80% of RMSE are improved with CC increasing from 0.07 to 0.91 on average. Additionally, the calibrated downscaled product provides finer information in local areas, capturing three times more spatial variabilities of urban precipitation against the original IMERG input data. The results highlight the necessity of improving urban observations for flood risk management at fine spatiotemporal resolutions.

Study of the improvement of the multifractal spatial downscaling by the random forest regression model considering spatial heterogeneity

“…The GPM has been adapted for the high-frequency channel, making it more sensitive to observations of trace and solid precipitation and allowing for a more refined rainfall distribution. 36 The GPM-IMERG precipitation data are currently widely used in precipitation studies. 24,37 The IMERG includes three types of precipitation products: "early run," "late run," and "final run."…”

“…The increased orbital inclination of the GPM allows for wider coverage of precipitation data than the TRMM. The GPM has been adapted for the high-frequency channel, making it more sensitive to observations of trace and solid precipitation and allowing for a more refined rainfall distribution 36 . The GPM-IMERG precipitation data are currently widely used in precipitation studies 24 , 37 .…”

Preparing for severe flooding: Flood risk management research leading to better flood preparedness

“…A new modelling approach for critical infrastructure networks that can be disrupted by flooding is explored by Schotten and Bachmann (2023). Other studies in this issue seek to develop important datasets for flood risk management applications, including the development of an extensive dam failure database to examine the probability distribution of earthfill dam breach parameters (da Silva & Eleutério, 2023), and the development of high-precision and high-resolution precipitation data using satellite estimate products (Zhuang et al, 2023).…”