Validation of IMERG Precipitation in Africa

Abstract

Understanding of hydroclimatic processes in Africa has been hindered by the lack of in situ precipitation measurements. Satellite-based observations, in particular, the TRMM Multisatellite Precipitation Analysis (TMPA) have been pivotal to filling this void. The recently released Integrated Multisatellite Retrievals for GPM (IMERG) project aims to continue the legacy of its predecessor, TMPA, and provide higher-resolution data. Here, IMERG-V04A precipitation data are validated using in situ observations from the Trans-African Hydro-Meteorological Observatory (TAHMO) project. Various evaluation measures are examined over a select number of stations in West and East Africa. In addition, continent-wide comparisons are made between IMERG and TMPA. The results show that the performance of the satellite-based products varies by season, region, and the evaluation statistics. The precipitation diurnal cycle is relatively better captured by IMERG than TMPA. Both products exhibit a better agreement with gauge data in East Africa and humid West Africa than in the southern Sahel. However, a clear advantage for IMERG is not apparent in detecting the annual cycle. Although all gridded products used here reasonably capture the annual cycle, some differences are evident during the short rains in East Africa. Direct comparison between IMERG and TMPA over the entire continent reveals that the similarity between the two products is also regionally heterogeneous. Except for Zimbabwe and Madagascar, where both satellite-based observations present a good agreement, the two products generally have their largest differences over mountainous regions. IMERG seems to have achieved a reduction in the positive bias evident in TMPA over Lake Victoria.

Validating the Integrated Multisatellite Retrievals for Global Precipitation Measurement in Terms of Diurnal Variability With Hourly Gauge Observations Collected at 50,000 Stations in China

“…Mayor et al () concluded that IMERG performed fairly well but still had a 2‐hr lag in the peak time in the countrywide mean diurnal cycle over Mexico. By using six gauge stations in Africa, Dezfuli et al () also proved the improved performance of IMERG in terms of diurnal cycle. However, to varying degrees, these studies were limited by factors such as data sources or research period and thus revealed only a few aspects of the diurnal characteristics.…”

Performance of the State-Of-The-Art Gridded Precipitation Products over Mountainous Terrain: A Regional Study over Austria

“…The satellite/gridded data produce the area average of precipitation in contrast with point measurements obtained with rain gauges. Earlier studies have shown that diverse altitude and geographic and climate conditions have greatly impact on the accuracy and performance of satellite or other precipitation products [2,[5][6][7][8][9][10][11]. For instance, in a study by Gottschalck et al [12] the overestimation of 3B42-RT over the Central United States is attributed to misclassification of cold cirrus clouds as precipitating systems.…”

Performance Evaluation of Version 5 (V05) of Integrated Multi-Satellite Retrievals for Global Precipitation Measurement (IMERG) over the Tianshan Mountains of China

“…After improvements in IMERG-V03, the NASA Goddard Space Flight Center (GSFC) introduced Version 04 (V04) of IMERG on March 22, 2017. Likewise V03, precipitation estimates from the IMERG-V04 were also assessed worldwide and the uncertainties and errors in the precipitation retrieval algorithms were identified over the diverse landscapes and climate systems [4,[33][34][35][36][37]. After modification in the precipitation retrieval algorithm of IMERG-V04, the version 5 (V05) was launched on November 20, 2017.…”