Weather Musings with KNAU Meteorologist Lee Born: Monsoon Patterns and Climate Change

Sep 15, 2017

In the latest installment of KNAU’s occasional segment “Weather Musings,” Meteorologist Lee Born answers listener-submitted questions about perceived shifts in the pattern of northern Arizona’s monsoon, as well as the effects of climate change on global weather. 

A monsoon over Kendrick Peak near Flagstaff
Credit Joe Coyle/joecoylephoto.com

Our first question comes from KNAU listener Mindy Degraff. She asks:

When I moved to Arizona 30 years ago, the monsoon seems to have a different pattern than it has today. Then, we could count on a hot and steamy morning, giving way to the monsoon rains between approximately 2 and 5 p.m., then a sunny and cooler evening. Now, it seems that the mornings are not so hot and the rains last all day and into the evening. Do you also notice this change in pattern? Why?

LB: When I first moved here in 2001, I felt like the typical monsoon day was just as you described; I have since changed my philosophy. I’m not so sure it’s a change in the pattern as much as a change in my observations—and the reality is that there is no typical or normal monsoon day.

There are many countless variables that affect the timing and intensity and nature of our rain: How much moisture is available and the stability of the atmosphere? Were there strong thunderstorms over Mexico recently? Is there rotation in the atmosphere? What is the overall steering flow on that day? Is there morning sunshine or debris clouds left over from nighttime storms?

Within each monsoon there are different cycles. Some days and weeks favor evening rain, others have more severe storms and hail, while others have barely any strong storms at all. And sometimes an entire monsoon season may display a certain personality or character of its own.

And now another question from KNAU listener Emma Rogers. She asks:

Please explain the drastic changes in weather throughout the world due to climate change.

LB: Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and oceans have warmed, the amounts of snow and ice have diminished, and sea level has risen.

In recent decades, changes in climate have caused impacts on natural and human systems on all continents and across the oceans. Impacts are due to observed climate change, irrespective of its cause.

To name a few of the drastic impacts observed around the world: Lower crop yields and an increase in the number and intensity of extreme precipitation events. Most recently tropical system Harvey was the largest rain event in U.S. history.

It is likely that extreme sea levels—as experienced in storm surges—have increased since 1970, being mainly the result of mean sea level rise. Heat waves are occurring more often and last longer.

In many regions, changing precipitation or melting snow and ice are altering hydrological systems, affecting water resources in terms of quantity and quality.

Glaciers continue to shrink almost worldwide due to climate change, affecting runoff and water resources downstream. Climate change is causing permafrost warming and thawing in high-latitude regions and in high-elevation.

Droughts, windstorms, fires and pest outbreaks have been detected in many parts of the world and in some cases are attributed to climate change.

Some warm-water corals and their reefs have responded to warming with species replacement, bleaching, and decreased coral cover causing habitat loss.

Continued emission of greenhouse gases will cause further warming and long-lasting changes in all components of the climate system, increasing the likelihood of severe, pervasive and irreversible impacts for people and ecosystems.  

These findings all from a large international group of scientists known as the Intergovernmental Panel on Climate Change.