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2024 Hennepin County All -Jurisdiction Hazard Mitigation Plan <br />Volume 2 — Hazard Inventory <br />TABLE 4.3.6A is derived from a statistical technique that utilizes data from multiple stations and is based <br />on observations. <br />TABLE 4.3.6A Precipitation frequency estimates for a point in central Hennepin County <br />The 100-year recurrence value for 24-hour rainfall is the most frequently cited value, and indeed, many <br />structure are designed for such an event. It is, however, important to note that shorter durations of <br />excessive rainfall can also overwhelm systems, and many have therefore been designed for 1, 3, or 6-hour <br />thresholds. Structural, civil, and hydrological engineers can provide further information on exceedance <br />thresholds used for infrastructure elements. Additionally, heavy rainfall over longer durations can <br />overwhelm systems, even when exceptional hourly rainfall rates are lacking. <br />Extreme rainfall, therefore, should be anticipated on a variety of timescales, and not just measured by <br />daily or 24-hour rainfall only. Radar estimates and automated rain gauges help forecasters understand <br />rainfall quantities for shorter and longer durations, and noteworthy rainfall events of many duration - <br />magnitude combinations have affected Hennepin County. <br />121 <br />