My last post focused on the southern part of the world’s most dramatic “West Coast” climate journey—the Pacific coast of South America, where the extreme dryness of the coastal desert heightens the dry-wet contrasts to both the north and south. This time I’ll move to the northern side of the desert, where the transition from lowest to highest rainfall levels (traveling toward the equator) is even more dramatic because it’s compressed into a much shorter distance—roughly 1200km/800mi. This creates the world’s sharpest rainfall gradient at sea level, which I’ve long assumed to be the case but thanks to my go-to reference The Earth’s Problem Climates (Glenn Trewartha) I now know I’ve been right.
As I wrote last time that compression is the result of the desert’s more-northerly-than-usual extension compared to analogous desert belts on the other continents, thanks to a complex combination of factors but in particular the position of the cold Humboldt/Peru Current. The northern part of South America bulges westward into the Pacific, forcing the current out to sea in northern Peru. Then as the coastline curves back to the east starting at the Peru-Ecuador border, it’s as if rainfall levels are trying to return as fast as possible to what they would’ve been if the desert had given way at the more typical latitude (around 20 degrees, much farther south at the Peru-Chile border).
Vegetation and rainfall along the coastal “bulge” from northern Peru to southern Colombia. (Vegetation map adapted from Trewartha; rainfall map adapted from various sources.)
Technically the two ends of that roughly 1200km distance—Lobitos, Peru, with about 50mm/2in of rainfall and Buenaventura, Colombia, in the vicinity of the world’s wettest sea level location with about 5000mm/200in—aren’t even the true extremes. A few hundred km farther north, Lloró, Colombia is the second-wettest place anywhere on earth, receiving about 13,000mm/500in. And the actual minimum of essentially zero rainfall is in northern Chile. But at those extremes the additional increase and decrease are, vegetation-wise, relatively imperceptible. (Coastal Colombia’s record precipitation levels have been less well explained than the Peruvian/Chilean desert’s record dryness, but given that the two are located so close together, according to Trewartha it would make sense if a single phenomenon is responsible for both—probably the cold current).
My own experience of this gradient is a lot less complete than the Chilean one despite the shorter distance. That’s mostly for practical reasons—on the northern end, the coast of northern Ecuador/Southern Colombia isn’t considered very safe and the Colombia side is mostly wild and roadless. To the south, the pattern is interrupted/obscured by the Gulf of Guayaquil and the Guayaquil metropolis. Given those limitations and my assumption that renting a car would’ve been less advisable than in Chile (though I never actually looked into it), I didn’t set out to capture it in any systematic way. But in 2018, tacked onto a few weeks in the Galápagos, I did get a driver to take me the 300km from Guayaquil north to Manta, mostly along the famous “Spondylus Route” connecting popular scenic and cultural attractions along the coast. That did allow for more flexibility than a bus would have, but I decided to keep things simple and limit my immersive experiences to some low-key hiking in one national park.
I was, though, also looking forward to the views from the car window. As you might’ve noticed on the maps above, particularly the vegetation map, a significant piece of the gradient is actually squeezed in between Guayaquil and the coast. That’s because rainfall also increases dramatically from the coast heading inland: the influence of the cold current rapidly decreases moving eastward just as it does northward. But that piece of the drive turned out to be underwhelming. I think this was because most of the vegetation was in leaf (the rainy season was supposed to have ended by then but it didn’t look like it), blurring the wet-dry distinction, and the gloomy weather probably made it even harder to see. The fact that there isn’t much natural vegetation left didn’t help either. Also, according to Trewartha the coastal vegetation in that region is more lush that might be expected from the low rainfall because of the fog drip and overcast skies, though I’m not sure why those factors wouldn’t have the same effect in the “real” deserts to the south. And his own maps do show desert creeping up the coastline. So, it’s still a mystery to me.
The national park I visited is Machalilla, which includes one of Ecuador’s few intact remnants of coastal dry forest.
Dry forest in Machalilla National Park, looking inland from the beach. (Despite the bad lighting you can see some bluish cacti poking through the canopy.) Later in the year it would be less green, but still not the desert the map would suggest.
Inside the dry forest. (It’s reminiscent of much of the arid zone of the Galápagos Islands, about 900km to the west.)
Large forest cacti.
In another zone of the park, a little bit inland and rising a few hundred meters to intercept the fog layer, the fog does have a clear effect on the vegetation. Being a function of elevation this fog forest isn’t technically part of the “long gradient” I’ve been focusing on, but it’s worth pointing out how the fascinating fog-generated landscapes of this region (a result of the same cold current) take different forms along that latitudinal gradient. Since it’s supported by fog “overlaid” on dry forest rather than on desert, the fog forest is basically indistinguishable from a rainforest—unlike the savanna-esque fog meadows in Peru that are dessicated for most of the year. (Unfortunately as far as I know it isn’t possible to hike between these two sections of the park, so this particular contrast isn’t worldview material.)
Fog forest (second-growth) in Machalilla.
Dropping below the fog again, north of Machalilla the forest gets perceptibly taller and the large cacti disappear. In certain areas these Ceiba or “ceibo” trees (C. trichistandra) are the most notable feature—they look a lot like green baobabs!
A few ceibos in (heavily disturbed) forest right along the road.
And from Manta, just a bit north of there, I flew to Quito—shifting my attention to mountains. I really wish I’d been able to continue north along the coast; if that ever becomes feasible it could be worth trying to drive (i.e. be driven) all the way from northern Peru to as far north as the road goes, during the dry season. Finding a representative string of accessible semi-intact natural areas won’t be easy. But, the hyper-compressed aspect of the gradient would make it a particularly good one for applying the transect ideas I’ve been thinking about (or ones I haven’t yet thought about) in a systematic way, even if the focus is mostly on human-dominated landscapes and how they reflect/impact the gradient.
Darren