Abstract
Precipitation is one of the major variables for many applications and disciplines related to water resources and the geophysical Earth system. Satellite retrieval systems, rain-gauge networks, and radar systems are complementary to each other in terms of their coverage and capability of monitoring precipitation. Satellite-rainfall estimate systems produce data with global coverage that can provide information in areas for which data from other sources are unavailable. Without referring to ground measurements, satellite-based estimates can be biased and, although some gauge-adjusted satellite-precipitation products have been already developed, an effective way of integrating multi-sources of precipitation information is still a challenge.In this study, a specific area, the Sicilia Island (Italy), has been selected for the evaluation of satellite-precipitation products based on rain-gauge data. This island is located in the Mediterranean Sea, with a particular climatology and morphology, which can be considered an interesting test site for satellite-precipitation products in the European mid-latitude area. Four satellite products (CMORPH, PERSIANN, PERSIANN-CCS, and TMPA-RT) and two GPCP-adjusted products (TMPA and PERSIANN Adjusted) have been selected. Evaluation and comparison of selected products is performed with reference to data provided by the rain-gauge network of the Island Sicilia and by using statistical and graphical tools. Particular attention is paid to bias issues shown both by only-satellite and adjusted products. In order to investigate the current and potential possibilities of improving estimates by means of adjustment procedures using GPCC ground precipitation, the data have been retrieved separately and compared directly with the reference rain-gauge network data set of the study area.Results show that bias is still considerable for all satellite products, then some considerations about larger area climatology, PMW-retrieval algorithms, and GPCC data are discussed to address this issue, along with the spatial and seasonal characterization of results.
Highlights
The development of remote sensing in recent decades has provided innovative resources to different hydrologic fields.Among the involved aspects, the availability of remote sensed data provided the knowledge of precipitation distribution at global scaleand with spatio-temporal resolutions useful for those climatological applications that do not require a long observation period
MBE1⁄2% 1⁄4 Xni1⁄4X 1 niP1⁄4ðo1ibÞPs−ðoibÞsPðeisÞt Á 100 where Po(ib)s and Pe(is)t are respectively the precipitation value provided by gauge data and the precipitation estimation provided by a satellite product for a single position/pixel, at the i-th time step with n being the number of considered time steps
These results show significant differences between magnitude of precipitation estimated by satellite products and reference data, resulting in a crucial underestimation by satellite products
Summary
The development of remote sensing in recent decades has provided innovative resources to different hydrologic fields. Difficulties in deriving precipitation estimates for hydrological applications based on satellite data and the necessity of measuring their associated uncertainty level, resulted in the development of a solid evaluation and validation scientific activity carried out by both developers and users. Beyond IPWG and PEHRPP activities, others studies have been carried out with similar objectives Some of these objectives compare different datasets to retrieve information about products and algorithms features. Because of its particular combination of geographic position, climatic features and morphology, this case study is very useful for retrieving different insights, both about strengths and weaknesses of estimates referred to as the considered geographic area and to general performances that may be expected using satellite estimates. Results of such analyses are presented and are summarized in the concluding section
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