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54 <br />The Fourth National Climate Assessment, published by the U.S. Global Change Research <br />Program in November 2018 (“NCA4”), finds that more frequent and intense extreme weather and <br />climate-related events, as well as changes in average climate conditions, are expected to <br />continue to damage infrastructure, ecosystems and social systems over the next 25 to 100 years. <br />NCA4 states that rising temperatures, sea level rise, and changes in extreme events are expected <br />to increasingly disrupt and damage critical infrastructure and property and regional economies <br />and industries that depend on natural resources and favorable climate conditions. Disruptions <br />could include more frequent and longer-lasting power outages, fuel shortages and service <br />disruptions. NCA4 states that the continued increase in the frequency and extent of high-tide <br />flooding due to sea level rise threatens coastal public infrastructure. NCA4 also states that <br />expected increases in the severity and frequency of heavy precipitation events will affect inland <br />infrastructure, including access to roads, the viability of bridges and the safety of pipelines. <br />The issue of climate change has become an important factor in water resources planning. <br />There is evidence that increasing concentrations of greenhouse gases have caused and will <br />continue to cause a rise in temperatures around the world, which will result in a wide range of <br />changes in climate patterns. Moreover, there is evidence that a warming trend occurred during <br />the latter part of the 20th century and will likely continue through the 21st century. These changes <br />will have a direct effect on water resources in the State, and numerous studies on climate and <br />water in the State have been conducted to determine the potential impacts. Based on these <br />studies, global warming could result in the following types of water resources impacts in the State, <br />including impacts on the Regional Water System and the Enterprise: <br />• Reductions in the average annual snowpack due to a rise in the snowline and a <br />shallower snowpack in the low- and medium-elevation zones, such as in the <br />Tuolumne River basin, and a shift in snowmelt runoff to earlier in the year; <br />• Changes in the timing, intensity, and variability of precipitation, and an increased <br />amount of precipitation falling as rain instead of as snow; <br />• Long-term changes in watershed vegetation and increased incidence of wildfires <br />that could affect water quality; <br />• Sea level rise, which could cause inundation of Regional Water System or <br />Enterprise assets and/or an increase in saltwater intrusion into groundwater <br />basins; <br />• Increased water temperatures with accompanying adverse effects on some <br />fisheries’ <br />• Increases in evaporation and concomitant increased irrigation need; and <br />• Changes in urban and agricultural water demand. <br />However, other than the general trends listed above, there is no clear scientific consensus <br />on exactly how climate change will quantitatively affect water supplies available to the Enterprise. <br />Sea Level Rise. Sea levels are expected to continue to rise in the future due to the <br />increasing temperature of the oceans causing thermal expansion and growing ocean volume from <br />glaciers and ice caps melting into the ocean. In 2018, the County’s Office of Sustainability <br />prepared a County of San Mateo Sea Level Rise Vulnerability Assessment, which estimated that <br />8.A. - Page 68 of 255 <br />696