Monsoon-Ready Trees: Why Tucson Trees Fail in Summer Storms and How to Prevent It

Written by Justin Tornatore, ISA Certified Arborist | TIMBERx

Abstract

Every summer, Southern Arizona trades extreme heat for violent thunderstorms, and every summer, uprooted mesquites and split palo verdes show up on the evening news. The National Weather Service defines the Southwest monsoon as June 15 through September 30 and warns that thunderstorm downbursts in Arizona can produce straight-line gusts over 100 mph [1]. But research on wind-thrown urban trees shows that the storm is rarely the only cause. Damaged roots, compacted or waterlogged soil, and poor canopy structure are recurring threads among the trees that fail [2][3]. In this article I review what peer-reviewed arboriculture research and University of Arizona Cooperative Extension say about storm failures in desert landscapes, and I lay out practical steps homeowners can take to help their trees come through monsoon season still standing.

Background: What a Monsoon Does to a Tree

Monsoon storms aren't the steady winds most tree research is built around. Thunderstorms produce strong, sudden downward rushes of air called downbursts or microbursts. NWS Tucson notes that thunderstorm gusts in Arizona almost always exceed 40 mph, and the strongest straight-line winds can do damage as severe as a tornado [1]. Trees don't need anything that extreme to get hurt, though. Damage to urban trees can begin at wind speeds as low as 25 mph when those trees already carry defects [3].

Local examples aren't hard to find. In October 2025, a short-lived microburst on Tucson's eastside split trees in half and toppled a 30-year-old saguaro and a nearly 20-foot tree. Residents described it as hurricane-force wind [4][5]. This past season, University of Arizona Facility Services reported working to replace about 35 campus trees damaged or knocked down by monsoon storms, including a palo verde in front of Old Main that was toppled on Aug. 27 [6].

The easiest way I've found to explain storm failure is to think of a tree as a sailboat. The canopy is the sail, the trunk is the mast, and the root plate is the keel holding everything upright. A dense sail catches more wind, a cracked mast snaps, and a weak keel lets the whole boat roll over. Nearly every storm failure comes down to one of those three parts.

What the Research Shows

Roots and soil decide most whole-tree failures. In a feature review in Arboriculture & Urban Forestry, Moore reported site inspections of 80 wind-thrown trees over 20 years. Damage to exposed lateral roots (87.5%) and loss of descending roots (88.8%) were found in most of them. Soil compaction at the base of the tree (65%), trenching near the trunk (58.8%), and waterlogged soil (56.3%) were also common [2]. In other words, the storm gave the final push, but the tree's history and how it was managed set it up to fall.

Site, storm, and defects stack on top of each other. Johnson and colleagues describe a "tree damage triangle" made up of site characteristics, the wind loading event, and the tree's own defects. Damage is worst where all three overlap. Their case studies identified large trees in limited spaces and roots severed during sidewalk repair as critical pre-existing conditions [3].

Irrigation shapes the keel. University of Arizona Cooperative Extension warns that mesquites can become unstable with excess irrigation, such as in lawns, because of rapid crown growth paired with limited root development. Drip emitters placed close to the trunk keep roots concentrated there. Moving emitters out to the dripline and beyond "will help establish a root system which gives stability to the tree and reduces the occurrence of tree toppling" [7]. The same publication notes that shallow, frequent turf irrigation can lead to palo verde toppling, and that circling roots from root-bound nursery containers can lead to tree failure if they aren't corrected at planting [7].

Dense canopies act like sails, but over-thinning backfires. Pima County Master Gardener guidance notes that trees with very heavy canopies are more likely to be injured by strong winds, and some thinning of internal branches may be needed to reduce that "sail-effect." The same guidance says never to remove more than one quarter of the canopy at one time [8]. A Pinal County Extension agent recommends light thinning of small, slender branches taken from several places throughout the tree, never all in one spot, to let wind pass through while leaving enough shade to protect tender bark [9].

Wet soil weakens the anchor. The International Society of Arboriculture (ISA) notes that strong winds can break branches and uproot trees, "particularly when combined with the softening of soils from heavy rain" [10]. During the monsoon, the rain and the wind often arrive in the same storm, and that's a tough combination for a shallow root plate.

Field Observations

From where I stand as an arborist, the trees that come down in a monsoon are rarely a surprise once you look at what's underneath them. The same patterns show up again and again:

• A fast-grown tree with a big, top-heavy canopy sitting on a small root plate.
• Roots cut for a wall, a pool, a paver patio, or an irrigation trench.
• Drip emitters still hugging the trunk years after planting.
• Trees planted too deep, or never freed from the circling roots they came with from the nursery.

Above ground, it's codominant stems with included bark, "lion-tailed" branches with all of their weight pushed out to the tips, and old topping cuts that have sprouted dozens of weakly attached shoots. As I've written before, fast-growing hybrids like the "Desert Museum" palo verde are convenient and attractive, but their structure needs attention early. That isn't a knock on the tree. Fast growth is a trade-off, and good structure has to be built on purpose.

Practical Recommendations

1. Inspect before June 15. Walk your trees in spring and look for ISA's red flags: large dead branches, cracks or splits in the trunk or branch unions, hanging limbs, cavities or rotten wood, mushrooms at the base, and cracks or heaving in the soil that suggest the root plate is moving [11].
2. Move the water out. Push drip emitters out to the edge of the canopy and beyond as the tree grows, and water deeply and less often rather than shallow and frequent [7].
3. Thin, don't top. Light, selective thinning of small interior branches reduces the sail effect. Never remove more than a quarter of the canopy at once [8][9]. Topping produces weakly attached shoots that are more likely to break in the wind, not less [12].
4. Build structure while trees are young. Subordinate competing leaders and remove crossing or poorly attached branches early, while the cuts are still small.
5. Protect the root zone. Avoid trenching, grade changes, and compaction under the canopy. These are among the most common factors found in wind-thrown trees [2].
6. Stay safe during and after the storm. NWS advises staying away from trees during severe thunderstorms and never touching a downed power line, even if it looks dead [1]. After the storm, resist the urge to do it yourself. Limbs under tension can react unexpectedly when cut, and anything touching a utility line is a job for the utility company [10].

Key Takeaways

• Monsoon downbursts can exceed 100 mph, and trees with existing defects can be damaged at far lower wind speeds [1][3].
• Research on wind-thrown trees points to roots and soil (damaged roots, compaction, trenching, waterlogging) far more often than to the storm alone [2].
• Deep, wide irrigation builds a stable root plate. Shallow turf watering and emitters at the trunk do the opposite [7].
• Thin lightly and selectively, and never top. Storm prep happens before June 15, not during the storm.

Stay safe out there this monsoon, friends.

Talk to an Arborist

Want a second set of eyes on your trees before storm season? Text Justin at (520) 451-8790 (texting is preferred over calling) or email Justin@TimberxTrees.com. TIMBERx is a veteran-owned tree care company led by Justin Tornatore, ISA Certified Arborist, serving Tucson, Oro Valley, Marana, Vail, Sahuarita, Green Valley, and Benson.

References

1. National Weather Service Tucson. Monsoon Safety. National Oceanic and Atmospheric Administration (n.d.; accessed October 2026). https://www.weather.gov/twc/monsoonsafety
2. Moore, G. M. (2014). Wind-Thrown Trees: Storms or Management? Arboriculture & Urban Forestry, 40(2), 53–69. https://auf.isa-arbor.com/content/40/2/53
3. Johnson, G., Giblin, C., Murphy, R., North, E., & Rendahl, A. (2019). Boulevard Tree Failures During Wind Loading Events. Arboriculture & Urban Forestry, 45(6), 259–269. https://auf.isa-arbor.com/content/45/6/259
4. May, P. (2025). Southern Arizona begins cleanup after wettest day in more than a year. KOLD 13 News. https://www.kold.com/2025/10/14/southern-arizona-begins-cleanup-after-wettest-day-more-than-year/
5. McKinney, J. (2025). Eastside storms cause damage to some properties. KGUN 9. https://www.kgun9.com/news/community-inspired-journalism/eastside-news/eastside-storms-cause-damage-to-some-properties
6. Sternberg, K. (2026). When monsoons take down campus trees, what's next? University of Arizona News. https://news.arizona.edu/employee-news/when-monsoons-take-down-campus-trees-whats-next
7. Schuch, U., & Kelly, J. (2012). Mesquite and Palo Verde Trees for the Urban Landscape (AZ1429). University of Arizona Cooperative Extension. https://extension.arizona.edu/publication/mesquite-and-palo-verde-trees-urban-landscape
8. Larson, P., Vance, L., & North, D. (2025). July Monthly Gardening Guide for Pima County. University of Arizona Cooperative Extension. https://www.extension.arizona.edu/publication/july-monthly-gardening-guide-pima-county
9. Gibson, R. D. (2019). Summer Pruning. July 2019 Garden & Landscape Newsletter. University of Arizona Cooperative Extension, Pinal County. https://extension.arizona.edu/sites/extension.arizona.edu/files/attachment/july-2019.pdf
10. International Society of Arboriculture. (2021). Storm-Related Tree Damage. TreesAreGood.org. https://www.treesaregood.org/Portals/0/TreesAreGood_Storm%20Related%20Tree%20Damage_0721.pdf
11. International Society of Arboriculture. (2021). Recognizing Tree Risk. TreesAreGood.org. https://www.treesaregood.org/Portals/0/TreesAreGood_Recognizing%20Tree%20Risk_0721.pdf
12. International Society of Arboriculture. (2021). Why Topping Hurts Trees. TreesAreGood.org. https://www.treesaregood.org/Portals/0/siteContent/pdf/Web%20TAG%20brochures/TAG_CBweb_Why%20Topping%20Hurts_v2.pdf