A parade of strong storm systems has brought much needed relief to drought-stricken California over the last month. However, this is turning into a case of “too much of a good thing” as atmospheric rivers – long, narrow currents of exceptionally wet air – are dumping massive amounts of precipitation, leading to widespread flooding. At their largest, atmospheric rivers can be up to 350 miles wide and 1600 miles long, carrying up to 15 times the amount of water in the Mississippi River!

While atmospheric rivers are a regular wintertime occurrence, accounting for 50% of the moisture falling in the western US, it’s the rapid succession of them that is leading to deadly flooding and landslides. Soil is becoming oversaturated – it simply cannot hold any more water. Additionally, burn scar areas, still recovering from massive wildfires, lack vegetation and roots to hold the soil in place, thus leading to hazardous debris flows.

We are currently just above 1 degree Celsius (1.8 degrees Fahrenheit) of warming since pre-Industrial times. With each degree of temperature increase, the atmosphere can increase its moisture content by 7%. Most of that extra water vapor is going to come from increased evaporation of oceans, lakes and rivers, as well as increased transpiration (water from plant leaves, stems and flowers). Increased moisture in the air can feed atmospheric rivers to grow wetter and more intense.

To mitigate flooding as well as defuse the power of water during these extreme precipitation events will require better infrastructure in urban areas to absorb water and hold onto it when the need arises (like drought during the dry season). The development of “sponge cities”, or, urban areas with abundant natural areas such as trees, parks, lakes, and plant-edged sidewalks would enable more absorption of water during rainfall events, preventing flooding. Integrating wetland areas that can also store water for future use would be beneficial. Installation of pervious concrete, which consists of 15 – 20% empty pore space, would allow water to flow through the concrete and drain out versus the hydroplaning that occurs off conventional concrete, which cannot absorb water. There are solutions that exist, with some cities already integrating them. More and more cities will need to adopt new techniques and infrastructure if they’re to adapt well to continuing geohazards due to climate change.

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photo: by Ulyana Peña