Assessment of satellite-based rainfall products using a x-band rain radar network in the complex terrain of the ecuadorian andes

Abstract

Ground based rainfall information is hardly available in most high mountain areas ofthe world due to the remoteness and complex topography. Thus, proper understanding of spatio-temporal rainfall dynamics still remains a challenge in those areas. Satellite-based rainfall productsmay help if their rainfall assessment are of high quality. In this paper, microwave-based inte-grated multi-satellite retrieval for the Global Precipitation Measurement (GPM) (IMERG) (MW-basedIMERG) was assessed along with the random-forest-based rainfall (RF-based rainfall) and infrared-only IMERG (IR-only IMERG) products against the quality-controlled rain radar network andmeteorological stations of high temporal resolution over the Pacific coast and the Andes of Ecuador.The rain area delineation and rain estimation of each product were evaluated at a spatial resolutionof 11 km2and at the time of MW overpass from IMERG. The regionally calibrated RF-based rainfallat 2 km2and 30 min was also investigated. The validation results indicate different essential aspects:(i) the best performance is provided by MW-based IMERG in the region at the time of MW overpass;(ii) RF-based rainfall shows better accuracy rather than the IR-only IMERG rainfall product. Thisconfirms that applying multispectral IR data in retrieval can improve the estimation of rainfall com-pared with single-spectrum IR retrieval algorithms. (iii) All of the products are prone to low-intensityfalse alarms. (iv) The downscaling of higher-resolution products leads to lower product performance,despite regional calibration. The results show that more caution is needed when developing newalgorithms for satellite-based, high-spatiotemporal-resolution rainfall products. The radar data vali-dation shows better performance than meteorological stations because gauge data cannot correctlyrepresent spatial rainfall in complex topography under convective rainfall environments.