The amount, distribution and timing of precipitation events — rain, snow and sleet, for example — is changing. In general, precipitation events are occurring less frequently, but are more likely to be intense. According to the U.S. Global Change Research Program’s 2009 report, Global Climate Change Impacts in the United States:
“Climate change has already altered, and will continue to alter, the water cycle, affecting where, when, and how much water is available for all uses….Climate change impacts include too little water in some places, too much water in other places, and degraded water quality. Some locations will be subject to all of these conditions during different times of the year.”
As with many climate change impacts, these changes will vary regionally. According to same report:
- Southern states are expected to see decreases in precipitation during the winter and spring months;
- Northern regions are expected to become wetter;
- The Pacific Northwest is expected to be wetter in the winter and drier in the summer;
- Nearly all parts of the United States (with the exception of Alaska) are expected to receive less rainfall in the summer).
The Union of Concerned Scientists offers one national and eight regional climate change impact fact sheets based on the 2009 report here.
Why Do Changes in Precipitation Patterns Matter?
Many climate models predict that individual precipitation events will become larger and less frequent. The consequences of this can be severe. For example, an inch of rain that falls over the course of a week is less likely to cause flooding or erosion than an inch of rain that falls during a single storm event.
These changes are not limited to individual precipitation events. Many regions of the United States are expected to see an increase in precipitation during the winter months, and a decrease in precipitation during the summer months.
Warmer temperatures speed the rate of evaporation, which decreases soil moisture and water availability. As a result, drought conditions will become more common. This, in turn, stresses ecosystems and increases the likelihood of wildfire. Droughts also negatively impact agricultural production.
Altered Precipitation: What Are the Consequences?
Changes in precipitation patterns will impact people and ecosystems by altering the availability of water throughout the year.
The predicted impacts of altered precipitation patterns include:
- Floods and droughts will become more frequent and more severe
- Wildfires are expected to become stronger and more common
- Changing ecological processes and species distributions in some aquatic habitats
- Loss of breeding or feeding territories for wetland-dependent species
- Declining crop and livestock productivity, due to increased droughts, floods and severe weather events
Changes in precipitation patterns may also compound other climate change impacts, such as: