Heavy rainfall in complex terrain: A view from space

This study examines rain retrievals from GPM Dual-frequency Precipitation Radar (DPR) and IMERG and compares those to surface-based precipitation measurements by ground radars and a dense network of precipitation gauges over the complex terrain of the island of Taiwan. A 32 year climatology of precipitation from the surface gages is compared to the 9 year climatology of GPM DPR overpasses to understand the biases and uncertainties in the DPR precipitation retrievals over complex terrain in heavy rain regimes. Results show that the heavy rain > 40 mm/hr is under represented by DPR. The regional and elevation dependencies of these trends are examined with respect to the near-surface clutter-free bin and vertical variability of rainfall. Additionally, ground-based rainfall measurements are compared with 9 years of IMERG rainfall products. It is found that IMERG significantly underestimates rain rates > 5 mm/hr compared to both ground observations and GPM DPR.

Further insights into the structure and microphysics of rain are gained using data from the 2022 PRECIP campaign. During the campaign, NCAR’s S-band polarimetric Doppler radar (SPOL) was deployed in northern Taiwan. A direct overpass of the DPR along an SPOL RHI on 29 June 2022 reveals differences in estimated rain rates and the microphysics in the column aloft that contribute to the precipitation estimates near the surface. This provides insights into satellite-based rainfall estimates over complex terrain.