Precipitation

For rain and snowfall, the trends driven by climate change differ by region. Global warming has changed the geographic pattern of precipitation; some areas are getting drier while others are getting wetter (Fyfe et al. 2012). Mid-latitude areas, such as the U.S. Midwest and Northeast, have experienced an increase in total precipitation. Sub-tropical areas, such as the U.S. Southeast and Southwest, on the other hand, have experienced a sharp decrease. As a result, the risk of both drought and flooding in differing regions of the U.S is increasing (NCA Chpt 2, p.26). Some sub-tropical areas, such as Texas, have not witnessed clear changes in long-term precipitation trends.

Climate change has also increased the intensity of heavy precipitation events (Min et al. 2011; Zhang et al. 2013). Even areas that see less precipitation overall, like the Southwest, have experienced this trend of concentrated (NCA Chpt 2 Fig 2.16, p.50).

Since 1958, every region of the United States has witnessed an increase in the amount of precipitation falling in the heaviest downpours. The increase is highest in the Northeast and Midwest, which have respectively seen a 74 percent and 45 percent rise (NCA Chpt 2 Fig 2.16, p.50). The trend is made possible by the ability of a warmer atmosphere to hold more moisture (Trenberth 2011).

Heavier snowfalls are also consistent with climate change. Many people hear the words “more snow” and instinctively think of colder temperatures, but the two are not necessarily connected. Relatively warm, just-below-freezing winter temperatures are favorable for heavy snowfalls. The U.S. actually tends to get more snow in warmer years, and the Northeast has experienced a dramatic increase in one-day precipitation extremes during the October to March cold season.


Storms

Climate change is increasing the amount of precipitation that falls in the heaviest storms (see precipitation section), but storms have other properties as well. Climate change loads storms with more warmth, moisture and energy, thus increasing intensity. General “storminess” as measured by winds speeds and ocean wave heights has increased in northern latitudes in recent years, particularly during winter months (Wang et al. 2009).