An annual rainfall metric integrates daily magnitude and frequency

Characterizing annual precipitation requires consideration of both daily magnitude and frequency. We introduce the Rainfall Magnitude–Rank Index (RMRI), a simple annual metric that requires no user-selected threshold or tuning parameter. RMRI is the largest integer k such that at least k days in a year record precipitation of at least k mm. For example, an RMRI of 26 indicates that at least 26 days recorded rainfall of 26 mm or more during that year. We evaluated RMRI in 329 quality-controlled station-years from 12 GHCN-Daily stations spanning contrasting hydroclimatic regimes. RMRI varied substantially across stations and years and was closely associated with annual precipitation amount and the frequency of moderate-to-heavy rainfall days. However, it was not interchangeable with annual total: among 129 same-station year pairs whose totals differed by no more than 1%, 18.6% differed by at least 3 RMRI units, with a maximum difference of 6. RMRI provides a concise, interpretable summary of annual daily precipitation magnitude–rank structure that complements established precipitation indices.