Assimilation of precipitation Estimates from the Integrated Multisatellite Retrievals for GPM (IMERG, early Run) in the Canadian Precipitation Analysis (CaPA)

Abstract

Study region: The study area covers the whole Canada at 10-km grid. Analysis was further done at the regional scale by dividing the study area into four climatic zones: Atlantic, Central, Prairie, and West Coast. Study focus: The Canadian Precipitation Analysis (CaPA) platform produces 6 h and 24 h precipitation accumulations on a 10-km grid over Canada by combining gauge observations with a background field provided by the Global Environmental Multiscale (GEM) numerical weather prediction model. In this study, precipitation data from the Global Precipitation Measurement (GPM) mission are included as an additional data source and are compared with CaPA benchmark estimates obtained without the Integrated Multisatellite Retrievals for GPM (IMERG Early Run, version 03 (V03)). The data used are for the summer of 2014 and we specifically considered the 6 h accumulations. The frequency bias indicator (FBI) and the equitable threat score (ETS) are used as performance criteria. Results were analyzed at four climatic regions. New hydrological insights for the region: Results show that IMERG improves the ETS and FBI for all regions, with the Central and Prairie regions showing the most improvements over the benchmark. In these two regions, statistically significant improvements in ETS are obtained for all precipitation thresholds considered. In order to assess the value of IMERG in more remote areas that are nonetheless important for water resources management in Canada, a fifth zone that has a lower gauge density was considered. In this region, ETS was significantly improved for precipitation thresholds up to 10-mm/6-h. We believe that combining satellite information with other remotely sensed product such as radar will provide a significant increase in skill, especially for mountainous regions where there can be beam blockages that can affect the quality of radar data. Keywords: Canadian Precipitation Analysis, IMERG, Satellite observation, Global Precipitation Measurement, Precipitation assimilation