2012-06-26_PWETC_AgendaPacket - Laserfiche WebLink

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This CSWMP includes sustainability in three of the Plan sections including this introduction; Section 4.0 Goals and Policies; and Section 6.0 Implementation Program and Funding. These Sections of the Plan provide additional background on what sustainability is and how it is a critical part of this Plan and what actions and approaches the City will take, related to its surface water management program, towards being more sustainable. 2.0 Physical Environment 2.1 Climate and Precipitation The climate of Roseville is considered to be continental and subhumid. Because of its location near the center of the North American continent, the Twin Cities metropolitan area (and Minnesota) experiences a wide variation in climate conditions (e.g,droughts and floods, heat and cold). However, even with these wide variations, climatologists have found four significant climate trends in the Upper Midwest (Minnesota Weather Almanac, Seeley, 2006): • Warmer winters • Higher minimum temperatures • Higher dew points • Changes in precipitation trends Estimates from the National Weather Service (NWS) TP -40 publication for the precipitation depth of a 24 -hour duration event for various return frequencies are presented in Table 1. The NWS is currently in the process of producing updated rainfall frequency estimates using a longer period of rainfall observations and state -of -the -art statistical methods. Updated estimates for Minnesota are anticipated in the spring of 2013. Table 1 Precipitation Event Frequency Return Frequency Precipitation Depth inches 1-year 2.4 2 -year 2.8 5-year 3.6 10 -year 4.2 25-year 4.8 50 -year 5.3 100- ear 5.9 In recent years, there has been more debate and discussion around the topic of rainfall depths and the frequency of larger storm event frequency. As described in an issue paper on this topic prepared during the development of the Minnesota Stormwater Manual, precipitation in Minnesota has been rising since the 1930s. This increase is attributed to an increased frequency of heavy to extreme precipitation events (Karl and Knight 1998). The State Climatologist suggests that the amount of precipitation occurring as large events has been increasing for decades, and that about 100 years ago that fraction was similar to or even higher than what it is today. The trends are changing and will likely continue to change. From a stormwater management perspective, these changes in precipitation may require larger pipes and ponds to capture and treat the runoff from more intense events. The City will continue to monitor the outcomes of Comprehensive Surface Water Management Plan ROSEV120222 City of Roseville Page 3