Flooding & Climate Change

Climate 101 > Flooding and Climate Change

In a Flash

• Flooding events stem from different factors, but will generally become more common and more intense, especially in areas that already experience flooding.
• Periodic floods are a necessary function in many ecosystems and agricultural regimes. However, extreme flooding can cause crop loss, property damage, public health and safety threats, and shortages of usable water.
• Government, private sector, and community stakeholders can use a combination of strategically planned development and engineered infrastructure to minimize flood risk.

The Climate Connection

Different types of flooding result from various combinations of human and (mostly) natural sources. Flood events worsen due to climate change impacts (warmer temperatures, extreme storms, and sea level rise) and human pressures (land use conversion and development, deforestation, engineered infrastructure, waste management, and groundwater extraction). Scientists can predict the regions vulnerable to flooding due to factors such as increased precipitation and sea level rise, but many drivers of floods depend on local and regional-level decisions and practices that remain difficult to predict.

Effects and Consequences

Different types of flooding result from various combinations of human and (mostly) natural source. These include flood events driven by rain, rivers, and oceans.

Rain: Storms capable of holding more moisture under warmer temperatures dump more rain over both shorter time periods (e.g. flash floods) and longer time periods. Human pressures (see floods driven by rivers, below) magnify the impact of floods primarily driven by precipitation.

Rivers: Floods along rivers result when water drains from smaller upstream tributaries to larger downstream river systems, and as water naturally pools in lower-lying floodplains. Under warmer temperatures [link], precipitation that previously fell in the form of snow and melted slowly over time during the spring, now falls all at once. Many human pressures increase the number and severity of river-based floods. These include:

1. Upstream deforestation and land conversion, which prevents absorption of floodwater in the headwaters of river systems.
2. Land development in the floodplains of rivers, replacing absorbent vegetation with concrete and other impermeable surfaces. Informal settlements in flood-prone areas outside the U.S. may contribute to floods, but often much less than large-scale commercial, industrial, agricultural, and formal residential development.
3. Artificial infrastructure, such as underground flood and sewer pipes and drains [link to combined sewer overflows] and concrete-lined culverts, channels, and reservoirs. These engineered infrastructure networks intend to control floodwater up to a certain point along certain parts of a watershed, but often exacerbate flooding along other parts of a river system, especially in less economically and politically powerful areas if water volume exceeds certain thresholds.
4. Improperly disposed waste, which accumulates and clogs flood drains.

Oceans: Coastal flooding can result from heavy precipitation or from river-based flooding when a river delta meets the ocean. But more commonly, coastal flooding results from:

1. Tides inching higher over time due to sea level rise.
2. Storm surge impacts [link], worsening due to stronger storms.
3. Pumping too much groundwater to the surface, which causes coastal land elevation to sink or subside.

Solutions

Ecosystems evolved to live in habitats experiencing periodic floods. However, land development Periodic floods benefit agriculture by redistributing sediment and nutrients that increase soil fertility. However, too much flooding can result in loss of crops and agricultural productivity.