Trends in Oceanic Precipitation Characteristics Inferred From Shipboard Present‐Weather Reports, 1950–2019

Abstract Shipboard present‐weather reports from 1950 to 2019 are aggregated and composited yearly and seasonally on a grid to characterize the global climatology and apparent long‐term trends in the relative frequency of four categories of oceanic precipitation: drizzle, moderate, and heavy non‐drizzle, precipitation associated with thunderstorms and deep convection, and frozen‐phase precipitation. Although ship reports are susceptible to subjective interpretation, the inferred distributions of these phenomena are consistent with observations from other platforms such as satellites and coastal surface stations. These distributions highlight widespread 70‐year trends that are often consistent across both annual and seasonal frequencies, with statistical significance at 95% confidence. The relative frequency of ship‐reported drizzle has largely increased in the tropics annually and seasonally, with linear best‐fit relative increases by as much as 15% per decade. Decreased relative frequencies have been observed in parts of the subtropics and at higher latitudes. Heavier precipitation has encompassed a growing fraction of non‐drizzle precipitation reports over the subtropical North Pacific and Mediterranean. The relative frequency of thunderstorm reports has declined over the open Atlantic but show positive trends over the Mediterranean and the western Atlantic. The trends in relative frozen precipitation occurrence suggest a poleward retreat of areas receiving frozen precipitation in the Northern Hemisphere. Possible mechanisms for these ship‐observed trends are discussed and placed in the context of the modeled effects of climate change on global precipitation.