Altered Precipitation

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. Increasing “very heavy” rain events have already been observed throughout the contiguous United States.

How are Precipitation Trends Changing?

The 2014 National Climate Assessment’s Climate Science Supplement explains that in general, wet areas are getting wetter and dry areas are getting drier, consistent with an overall intensification of the hydrological cycle in response to global warming.

These changes may be especially pronounced through different regions and different seasons, which can have further impacts to water resources that are heavily influenced by snowpacks and the timing of snowpack melts.

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.

Implications for Land Trusts

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.

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:

• greater flood risk
• shifting habitats and seasons, which may especially effect migrating species.

Tips for Planning: What Land Trusts Are Doing

Cooperatively Working Towards Conservation Goals.

Land trusts are responding to on-the-ground impacts of altered precipitation trends in various ways. Some groups are implementing adaptation projects such as removing barriers to surface waters or planting less water-dependent tree species. In addition to employing strategic conservation planning to reduce risks and enhance resilience, some land trusts are also supporting efforts to mitigate greenhouse gas emissions to reduce the extent of future climate change.

Land trusts must determine the right planning approach for their organization, however, increasingly, conservation organizations are working with their communities to identify opportunities to reduce vulnerabilities and prepare for changing temperatures. Agencies are making similar strides to implement projects that reduce risks and plan for resilience by incorporating adaptation, mitigation, and engagement into their strategic goals and objectives. For example, the U.S. Fish and Wildlife Service’s Strategic Plan for Responding to Accelerating Climate Change identifies seven planning and development goals to support sustainable landscapes. Conservation groups are increasingly partnering with agencies as well as other nonprofits and for-profit organizations to respond to this global challenge at local levels.

Building resilience for multiple management objectives.

Resilience describes the ability of a system to persist through extreme change. By working to identify and reduce potential threats land managers can build resilience and achieve multiple management objectives. Assessing vulnerabilities is a critical step in the strategic conservation planning process that helps land trusts identify key threats to resources. Adaptive management planning enables conservation practitioners to implement interventions to reduce vulnerabilities and to monitor and revise strategies as new information becomes available. There is no one-size-fits-all solution to addressing management challenges associated with warming average temperatures, however, planning that acknowledges vulnerabilities can help land trusts better achieve their conservation objectives.

Learn More

• Climate Change and Water Resources Management: A Federal Perspective, USGS
• Heavy Precipitation, EPA
• Weather and Climate, EPA
• U.S. Drought Portal
• Water Resources, U.S. Global Change Research Group
• Water, Climate Change and Forests: Watershed Stewardship for a Changing Climate, USFS