Reliability of the IMERG product through reference rain gauges in Central Italy

Satellite precipitation observations represent the future of climatology, as they allow continuous assessment of climate parameters over the entire earth's surface. Today, climate detection methods are in a transitional period where satellite data are not yet perfectly calibrated, while ground-based weather stations are still the most reliable detection methods. Precipitation is one of the most important climatic parameters, but at the same time it is complex to measure accurately by satellite. In this context it is essential to evaluate the reliability of a very useful and universally recognised satellite product, the IMERG V06 Final Run with validated weather stations in Central Italy. This could allow, on the one hand, to assess the accuracy of this satellite product compared to rain gauges, and on the other hand a better calibration at local scale. The analysis involved as many as 154 rain gauges in an area of about 12,600 Km2 , so as to cover the area in a punctual way; in this context, two different comparison procedures were tested, pixel-to-point and pixel-to-pixel at annual and monthly scale, in the period 2001–2021. The results showed an overestimation of rainfall by the IMERG product, compared to rain gauges of about 200 mm per year, while in the coastal and hilly areas, IMERG's performance is even worse, overestimating precipitation by almost 1000 mm. This study showed that the pixel-to-pixel procedure proved to be the most reliable, showing the existence of a linear relationship between altitude and the differences between rain gauges and IMERG data, with an annual linear regression explaining up to 82% of the overall variance, allowing a possible calibration of the satellite product in the area.