Frequency of precipitation across the northern U.S. corn belt
Knowledge of the frequency of precipitation events can aid in managing water resources, but little is known concerning the regional variability in the frequency of daily precipitation events in the northern U.S. Corn Belt. The frequency distribution of daily precipitation events, varying from 0.25 to 102 mm, was examined at 15 climate stations in Minnesota, South Dakota, Iowa, and Wisconsin. Data were available from 1898 to 1997. Annual precipitation and frequency of precipitation events increased from the NW to the SE across the northern Corn Belt. The frequency of daily precipitation events (of at least 0.25 mm) at all stations remained fairly persistent (at about 20%) during winter then increased during spring before attaining a maximum near 35% in late May or June. The frequency of events then declined to about 25% by late August before approaching a secondary maximum of about 30% in September. The frequency distribution of daily precipitation events was skewed, with more frequent events occurring earlier in the year at all but the two most eastern stations. The transition from winter to spring precipitation patterns was delayed about 15 days at western as compared with eastern stations. Precipitation events were twice as frequent in the spring than in the autumn at western stations and 30% more frequent in spring than in autumn at eastern stations. This study suggests that daily precipitation events in the northern Corn Belt occur with greater frequency in the SE than in the NW and in the spring than in the autumn. This regional and seasonal variability in precipitation must be considered when designing hydrologic systems and managing agricultural and natural resources.
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