Laserfiche WebLink
r- American Water Works <br />Association <br />lne Autfioritr,3tiv r csoi3r ~ an Sa r ~NatF~r"' <br />~~ <br />WRTER <br />limate change is already happening. Over the past century, global average surface tempera- <br />ture increased by approximately 0.6 degrees Celsius. Warming is expected to accelerate dur- <br />ing the current century. The modest warming to date has not been evenly distributed over the <br />surface of the globe. In particular, arctic areas have warmed more rapidly than other areas. <br />Climate model simulations also suggest that future warming will tend to be more pronounced in <br />the higher northern latitudes. <br />As for impacts on water resources, warming over the past half century appears to be associated <br />with reduced spring snowpacks in some of the mountainous areas of the western US. In California's <br />Sacramento River Basin, spring runoff has been peaking earlier and there has been acentury-long <br />downward trend in late spring and early summer flow as a proportion of total annual flow. Warmer <br />temperatures have contributed to rising sea levels through oceanic thermohaline circulation, which <br />transports warm water poleward increasing glacial melt. Higher sea levels have caused saltwater <br />intrusion into freshwater estuaries and aquifers in some areas. <br />Global climate change will likely alter the hydrologic cycle in ways that may cause substantial impacts <br />on source water availability and water quality. The amount, intensity, and temporal distribution of pre- <br />cipitation are likely to change. Warmer temperatures will affect the proportion of winter precipitation <br />falling as rain or snow, how much is stored as snow and ice, and when it melts. <br />Long-term climactic trends could trigger vegetation changes that would alter a region's water bal- <br />ance. In forested areas, the combination of warmer temperatures and drying soils caused by earlier <br />continued on inside <br />