Appendix G – Climate Change Considerations

Overview and Purpose

Climate change (i.e., increasing precipitation and temperature and sea level rise) and its implications for stormwater management design and implementation were important considerations during the revision of this Manual for the following reasons:

  • Previous guidance regarding design storm precipitation (e.g., 10-, 25-, and 100-year storms) is no longer relevant due to the shift in climate and precipitation that has been observed since the development of the original Connecticut Stormwater Quality Manual.
  • Increasing trends in precipitation also include observed and projected increases in average precipitation amounts, which has implications for smaller, more frequent storms including the water quality storm.
  • Rising sea levels have begun and are projected to continue to result in rising groundwater levels in coastal areas of Connecticut and elsewhere along the eastern coast of the United States. Rising groundwater has implications for stormwater infiltration and treatment practices along Connecticut’s coast.
  • The design life of many stormwater BMPs and related stormwater infrastructure is intended to be well over 20 years. Over this period, it is possible the design limits could be exceeded as a result of changing precipitation conditions, thereby reducing the effectiveness of the stormwater BMP or resulting in failure of the stormwater infrastructure.

This Manual incorporates various climate change and resilience considerations for stormwater management design and implementation:

  • Preserving pre-development site hydrology using LID site planning and design strategies and structural stormwater BMPs
  • Updated design storm precipitation for stormwater quantity and quality control
  • Sea level rise and other considerations for stormwater BMP siting and design in coastal areas
  • Design considerations for mitigating the potential negative impacts of climate change on stream temperatures and nutrient loads.

This appendix provides additional details regarding climate change and stormwater impacts in Connecticut, including the basis for the selected approach to incorporating updated design storm precipitation and other climate change considerations into this Manual.