If drought is explained as imbalance between available and needed water, then megadrought is explained as this imbalance lasting for at least 20 years.  Seems like a long time, doesn’t it?  Children are born, raised, and leave their parents over 20 years.  The same span takes us from youth (me 20 years ago) to mid-life (me now).  Or mid-life into older age.  Pets have come and gone. 

I couldn’t tell you exactly what I was doing 20 years ago and all the events that have happened since.  Meanwhile a drought would have persisted the whole time.  If 20 years feels like a long time, imagine that megadroughts can persist for hundreds of years. 

Scientists study tree rings, like those in the picture below, to understand past climate. Wider rings are good years, while narrower rings are dry years.  A study of many tress across the western US since the year 800 shows 4 megadroughts: the late 800s, mid-1100s, the 1200s, and the late 1500s. Megadroughts are thought to play a role in ending civilizations such as the Anasazi of the North American Southwest, the Mayan of Mesoamerica, and the Yuan Dynasty of China.

Cross-section of tree ring from a ponderosa pine from Tucson, Arizona. From Science News Digital.

Many think we are in the midst of a megadrought that started around 2000.  Now that we are 20 years in, it is hard to say if it’s over.  One or two “good” years does not make up for years of dry ones.  A few dry years combined with unusually warm temperatures is a recipe for extreme dryness.  Soils dry, plants demand more water that is not available, plants die, tree rings narrow, trees dry, and fires ensure.  It is understandable how civilizations end, no longer able to manage with scare resources.  It is hard to say it’s over, and it’s also hard to say it’s just beginning.  We may be in a smaller cycle of 20 years or a larger cycle of hundreds of years. 

Lake Mead is predicted to fall to a record low this year while water managers assure us that there is enough supply for this summer. It is not clear what happens as the next 20 years go on. In the meantime, do your part to be mindful of water use.