Thanks to some fortuitous rains due to tropical Eastern Pacific cyclonic systems in October 2018, the stage was set for a good wildflower bloom in the spring of 2019. I’ll discuss the precise dynamics of what constitutes a good bloom year in a separate post sometime, but the most basic initial requirement is widespread soaking rains of at least one inch across the lower deserts where wildflower seeds await the trigger provided by adequate moisture.

The boundary of Havasu National Wildlife Refuge where sand dunes meet gravelly hills at the base of rugged Lower Sonoran Desert mountain ranges.

This one inch or so of precipitation is not an insignificant barrier for desert weather systems to overcome! After all, a full inch of rain in one storm system represents approximately 20% to 25% of the average annual total in most of both the Lower Sonoran and Mojave Deserts. Storms producing one inch of rain are commonplace in most other ecozones. But those ecozones are not hyperarid deserts, and for them to get an inch at once is roughly equivalent of wetter places receiving 4 inches of rain in one system. In other words, possible, but fairly infrequent and not necessarily an annual event either.

A different view of the dune and rugged hills scenery that flanks this part of the Colorado River.

Fortunately, two tropical systems in October 2018 did meet this threshold of rainfall. The first was Hurricane Rosa, whose remnants passed over the north-central Baja Peninsula and into southwestern Arizona on Mon-Tues, October 1-2, 2018, at the very end of what could maybe still considered the summer monsoon season. Most tropical cyclonic systems reaching the desert southwest are monsoonal in nature, although the official end of the season is usually September 15. However it is not unheard of for occasional late hurricane arrivals to extend the monsoon by an extra week or two, or simply arrive even later in November in a technically non-monsoonal way, but with similar tropical effects regardless.

Several showy species of dune wildflowers spread their leaf rosettes across the sands at Havasu NWR in late December, 2018. Game on!

Rosa’s path fell mostly somewhat to the east of Mohave County AZ, where I live, and rainfall was disappointing here at generally near or under a tenth of an inch.  But only 100 miles farther east and throughout the rest of the state, most of Arizona received one to three inches from Rosa, and in some places over five inches of rain fell in the mountains. But residual moisture left behind in the wake of Rosa’s departure provided enough fuel for scattered rain showers a day later on October 2, dropping amounts of .25″ to .5″ in patches of desert around the county. While this was better than zero, it also isn’t really enough to kick-start a meaningful wildflower germination wave.

Several wildflower species prepare themselves for the pending show, including four sizable rosettes of dune evening primrose (Oenothera deltoides) and the first early flowers of a sand verbena (Abronia villosa). Both species will become several times larger and bear numerous flowers by February or March 2019, in only 8 to 12 weeks.

Rescue came in the form of a second tropical system, Hurricane Sergio, who arrived from the southwest on Friday, October 12, 2018. Sergio followed a path that was very similar to that of Rosa across Baja but stayed significantly farther southeast over Mexico, only entering southeastern Arizona near Tucson. But despite this farther-away track, Sergio left behind a big plume of high-moisture air that was present over the deserts when a strong early-season Pacific low came inland on Saturday, October 13.

The first flowers of suncups (Camissonia brevipes, aka Chylismia brevipes) hoist themselves into the air. On this winter solstice day in 2018, these were the only open flowers I found, although there were plenty of plants readying themselves for a much more floriferous display in 6 to 10 more weeks.

As the dynamic Pacific trough migrated eastward across the deserts of California and Arizona, it lifted this moisture-rich air and created heavy storms that dropped large amounts of rain in short times. As it turned out, widespread totals of 1 to 2 inches of rain were dropped over the lowest, driest desert regions of the Lower Colorado River Valley. Just what the doctor ordered to get the mass display going!

Like the suncups above, this was the only dune evening primrose I found open. And also similarly, there are many more preparing for a pretty decent showing in 6 to 10 more weeks.

Contrary to popular belief, rainfall that occurs in the middle of winter or early springtime (in other words after late December) usually has little effect upon wildflower seed germination. The best displays of flowers start with these critical, but never assured, autumnal rains in October or November. About the latest that most annual wildflower seeds will respond to rains is early or perhaps mid-December.

Sand verbena (Abronia villosa) is one of the showiest of sand dune wildflowers. In good years, they can cover thousands of acres in a blanket of hot pink flowers, often mixed with gold, white, and blue flowers from their companion species.

The reason that most annuals do not respond to cold winter rains is simply because if they did, there would probably not be enough time for them to grow, develop adequate size, flower, and set viable seeds before the return of hot weather. At these low elevations and fairly southerly latitudes, the Lower Sonoran Desert heats up quickly and might easily be reaching the 90s F by mid-March with diminishing odds for sustaining rainfall. It simply behooves annual plants to already be done with most of their life cycle by the time that happens. And this is why fall rains are really the hidden key to understanding and predicting mass floral displays in the deserts of the USA and Mexico.

Close up of the first sand verbena flowers of the 2019 season, actually already starting in late 2018. A portent of the future, one would hope….

This is not to say that winter rains are not important to spring wildflower displays. They are. While winter rains might not actually initiate the vernal shows, they are extremely important to sustaining them if they manage to get started in October or November the year prior. Indeed, it has been known to happen that a beautifully timed and abundant start to a mass color event in the fall was cut short by a dry winter, when rains failed to arrive in sufficient quantity to keep the seedlings alive or enable them to reach their full potential. Excess warmth or even unusually harsh freezing temperatures have also caused reductions in spring displays, particularly in conjunction with dryness. There are several ways for a good start to be derailed.

A mustard with oak-like lobed leaves joins a sand verbena and an Ajo lily (Hesperocallis undulata) on the Havasu NWR dunes as the sun goes down on the winter solstice, 2018.

Perennial wildflowers are much less dependent upon a perfectionistic combination of timing, quantity, and subsequent follow-up precipitation in order to put forth good displays. Perennials by definition already exist in a form other than tiny seeds, and can capitalize upon varying seasons and amounts of rainfall, or even snowfall in some cases. They can respond better to lower amounts, and later timing. So a dry fall followed by a late-starting but fairly wet winter can still result in some impressive mass displays of perennials, although the famous annuals might be nearly missing or even absent.

Ajo lilies, also known as desert lilies, crowd the dunes with foliage as a prerequisite to their pending bloom in another couple of months. Ajo is the Spanish word for garlic, and might refer to either the size or the edibility of the bulbs. But Ajo lilies (pronounced AH-ho) don’t actually have anything resembling a garlic-like scent, so the comparison only goes so far.

Perennial plants that often flower well in average rainfall years when annuals are sparse or absent include most cacti, ocotillos, and sometimes yuccas; desert trees like palo verde and ironwood; and shrubs like brittlebush, paperflower, and chuparosa. Other trees, woody shrubs, perennial herbs, and many yuccas and their relatives also tend to require a better than ordinary year in order to really flower profusely, and many of them will hardly bloom at all in a dry year.

Awaiting the spring 2019 bloom of the Ajo lilies. The plants are just leaves as of December 2018, and flower spikes will start emerging before long.

Hesperocallis plants do not emerge to photosynthesize or flower unless there has been a substantial autumn rain that penetrates the sands to where the bulbs are buried, which is anywhere from 15 inches to 24 inches deep. In dry years they stay dormant just like the annual wildflowers to, albeit as bulbs rather than as seeds. I will return to this scene in late February 2019 to check upon their progress and take photos of the dramatic tall and fragrant white flower spikes that resemble Easter lilies.

Other plants also inhabit the Havasu National Wildlife Refuge, such as this scene of dense brush thickets lining the marshlands of the Colorado River banks.

In a really drought-stricken cycle, sometimes the succulent cacti are the only plants actually doing much blooming at all. Again, variances are normal and hard to predict precisely until only a couple of months in advance, although as emphasized above if fall was dry then spring won’t likely yield an epic bloom in any case.

Several fan palms (Washingtonia robusta in all likelihood) join the marshland community. The palms are probably suburban escapees, grown from seeds deposited by birds feeding on the fruits of palms growing in nearby Lake Havasu City, AZ or Needles, CA. They are not actually native to the site.

Of course Havasu National Wildlife Refuge was created primarily to protect wetlands and waterfowl habitat along the Colorado River, although significant areas of sand dunes and riparian hillsides flanking the watercourse are simultaneously given coverage. The wetlands along the Colorado River host a variety of different water-loving species, obviously in stark contrast to the species that survive on the arid hills only a few meters away.

Eroded alluvial deposits laid down by the Colorado River eons ago form conglomerate bluffs overlooking the watercourses that thread the marshlands.

Despite the importance of the Colorado River corridor to a wide variety of waterfowl, shorebirds, raptors, and migratory passerines, the marshlands themselves are no longer primarily native species. There are a couple of invasive ones that dominate large swaths of terrain, including tamarisk trees (aka salt cedars, Tamarix sp) and common reed grass (Phragmites australis) which supplant the native vegetation of cattails (Typha latifolia and T. angustifolia), bulrushes (Cyperus sp), seep willow (Baccharis salicifolia), and arrow weed (Pluchea sericea).

Dry dunes to dampness within 100 feet – layers of different vegetation add pleasing contrast to this scene.

The invasive species issue in Havasu NWR is not limited to plants either. Wild boars (Sus scrofa) are feral pigs that have somehow found their way to the Colorado River corridor and have taken a toll on both the wetland vegetation and the birds that nest or feed in them. While unable to survive the arid and largely barren desert nearby which offers them very little in the way of food and absolutely no water, they are nonetheless quite able to damage the habitat most necessary to birds and other mammals.

I surprised this sow and four piglets two years ago when I last visited this area in March 2017. The white flowers are Ajo lilies (Hesperocallis undulata).

Wild pigs are extremely invasive in numerous habitats worldwide, and cost farmers and wildlife managers billions of dollars annually in lost crops, habitat damage, and control costs. They are capable of breeding quickly, with females getting pregnant within their first year and bearing upwards of 4 to 8 young per litter, more than once a year on average. They are omnivores that eat everything, and are smart enough to learn to avoid humans when they sense a threat after only one encounter. Controlling them is a perpetual headache in wilderness zones, croplands, and sensitive wildlife habitat.

The wild pigs escape from the human intruder by running away through the dunes and into the denser marshland vegetation where they can hide.

Several ducks and coots feed on the surface of a small pond within the bog.

The winter solstice sun goes down over the refuge on Friday Dec 21, 2018.

A departing cold front cloud deck clears the way for a tremendous blazing sunset.

Looking west over the Colorado River into California.

Rapidly eroding mud hill badlands topped with sand dunes drop down to river level.

The moon happened to be full on the winter solstice of Dec 21, 2018, enabling this pleasant view to the east as it rose through a thin veil of cirrus clouds.

Farewell to the year 2018 as it draws to a close…

A couple of parting shots of this same region taken on Wednesday March 8, 2017. The Ajo lilies were in grand bloom over many of the dunes, and all of the other flowers featured above were also present.

A peaceful sundown scene from two years before this post was written of the same tranquil river and desert view. Serene and healing.

I will return to see how the developing wildflower display on the dunes shapes up in a couple more months. Hopefully in between early January and early March 2019, we will receive some additional rains that enable full development of the already decent-sized seedlings we see present. Since wet winter storms from the Pacific are a good bet in this part of the desert, odds are pretty high that spring 2019 will be a good year at this site. This is also true for the other portions of California, Arizona, Baja, and Sonora MX that also were blessed by the precipitation brought by the twin hurricanes, and augmented by additional rains that fell in early December. Stay tuned!

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Addendum for Sunday, January 6, 2018: Only a day after I posted this, a winter storm moved across the Havasu National Wildlife Refuge dunes, providing an estimate of about .45 inches (11 mm) of rainfall. The official Lake Havasu City total, presumably a station at the airport only a few miles away, was .43″, and Needles CA only about 20 miles north got .52″, so this figure is probably pretty close to correct.

Once again, while this would not be enough rain in a dry year to initiate seed germination or bulb growth, and it would be too late as well were it the first rain of a dry winter, since it is falling upon already-established plants that are actively growing it is highly useful. A half inch of rain falling at a cool time of year when evaporative rates are low will give a much-needed boost of hydrological resources to the mid-sized plants, enabling them to continue setting buds and side-branches which means greater floral density in a couple of months.

Another potentially similar or stronger storm is possible next weekend, about January 13. If this materializes, I will add a second addendum beneath this one.