Climate Change Will Delay Southwest Monsoon Season

Climate change models say that the summer southwest monsoon season will return to the American southwest, but it will start coming later in the year, which is a problem because crops will just be starting to grow as the days get shorter in the fall. That’s the conclusion of a new study in Journal of Geophysical Research, headed up by lead author Benjamin Cook, a climate scientist with joint appointments at Columbia University and NASA.

The new models suggested that global climate change will set up a chain reaction that delays the monsoon rains. Drier winters, with less rain or snow to the north, will create drier conditions that make it more difficult for clouds to form in the spring and early summer. The rains wouldn’t be able to begin until wetter air eventually arrived on changing air streams in September or October. In the past, the southwest monsoon generally occurred in July and August.

Farmers and ranchers in the study region, which includes northern Mexico as well as southern Arizona and New Mexico, depend upon the monsoon rains for most of the year’s rainfall. The area has been concerned about the affects of climate change ever since a devastating 2011 drought, which also affected states to the east including Texas and Louisiana. In that year, both New Mexico and Arizona experienced their hottest summer ever recorded to date. They were also hit by record-breaking wildfires, including the Las Conchas wildfire, which threatened the Los Alamos National Laboratory, where the first atomic bomb was developed.

Although 2012 was an even more severe drought year for the American Midwest, sending grocery prices through the roof, September rains finally arrived to provide some water to the southwest. Ironically, the late monsoon dumped too much water, creating flash floods in Las Vegas, Nevada.

A late rainy season is, of course, no better than no season at all. By mid-July during last summer’s drought, CNN was already reporting that the southern plains and southwest had lost about $12 billion in economic losses to farmers and ranchers. By the end of the crisis, some observers had compared the drought disaster in the midwest to the 1930s dust bowl, which contributed to the length and suffering of the Great Depression.

However, the late season will still create challenges. Cities like Phoenix and Tucson will need to stretch their water reserves to fight potentially dangerous wildlifes. In 2005, the late monsoon forced cattle ranchers to buy feed, since there was no grass, greatly increasing their costs.

Since the monsoon provides 70 percent of the rainfall for a region that supplies food to about 20 million people, people will have to plan how to use the water wisely in an era of changing climate.

[photo courtesy Brian Jackson and flickr]