The validation of satellite precipitation estimates with ground observations plays a vital role in the search for sources of errors. Additionally, satellite estimates and their performance change with precipitation types, intensities, and geographical conditions. An international team of scientists led by Rajani Kumar Pradhan of the Czech University of Life Sciences recently published an article reviewing the Integrated Multi-Satellite Retrievals for GPM (IMERG) validation studies around the globe characterized by various locations, topography, and climatic regions. Their results show that the distribution of IMERG validation studies worldwide is not uniform. For instance, countries like China, USA and India dominate with the highest number of studies while research over much of Africa is lagging behind. Results showed that IMERG represents the spatial mean precipitation and spatio-temporal variation throughout the validation regions. However, in terms of intensity, IMERG revealed various under/over estimations that vary with physical conditions, season, and precipitation types. The statistical matrices used to evaluate the IMERG precipitation have improved from daily to monthly and annual scales. It has been revealed, that IMERG has comparatively poor performances in winter than in other seasons, resulting from the difficulties in detection and estimation of snowfall and light precipitation. Like other satellite estimates, IMERG has problems estimating precipitation over complex topographies, and orographic precipitation. In terms of extreme precipitation, IMERG can detect and estimate the precipitation from storms, but it fails to do so at the storms’ centers. The hydrological evaluation results found significant under/over estimations based on the hydrological model used, study area and evaluation types. The upgraded IMERG versions strive to improve these estimations as the importance of IMERG and range of potential applications of GPM further expands. The full article is available in the journal ‘Remote Sensing of Environment’, vol. 268 – here.
Water & Climate 