Chaco
Chaco Geography & Climate
Geography
The Chaco is an enormous alluvial plain built from sediment washed off the Andes, covering about 60 per cent of Paraguay and extending into Bolivia, Argentina and Brazil.
Flatness
It is almost perfectly level. The land falls a few centimetres per kilometre from the Andean foothills to the Paraguay river, over hundreds of kilometres, which means water does not drain so much as spread. The only relief is Cerro Leon, a low range of hills in the far north-west that rises a few hundred metres and looks like a mountain range by comparison.
Wet east, dry west
The Bajo Chaco near the river is palm savanna, seasonally flooded, with caranday palms standing in water for months. Moving west, rainfall falls away steadily to under 400 millimetres in the far corner, and the vegetation becomes dense, spiny, grey-green thorn forest — quebracho, palo santo and cactus — that is genuinely hard to walk through.
Water
The defining problem. Groundwater in much of the region is saline and undrinkable, surface water is seasonal, and the colonies were built on catching rainwater from roofs into tanks. A pipeline from the river now supplies the central colonies.
Salt lagoons
Shallow saline pans in the centre of the region attract flamingos and waders.
Palo borracho and quebracho
Two trees define the vegetation. The palo borracho or drunken tree swells into a spined bottle-shaped trunk that stores water through the dry months and flowers pink when almost leafless. The quebracho — the name means axe-breaker — is so dense it sinks in water, and was logged across the region for a century for the tannin in its heartwood, which supplied the world’s leather industry.
Wildlife habitat
The dry Chaco is the largest continuous dry forest in South America, and among the least protected.
Climate Patterns
The Chaco has one of the harshest climates in South America, and it gets harsher moving west.
Heat
Summer, from October to March, is severe. Daytime temperatures routinely exceed 40°C and the region holds the highest reliably recorded temperature in South America — over 45°C, measured in the Paraguayan Chaco. Humidity in the east makes it worse; the dry west is at least dry heat. Work stops in the middle of the day.
Winter
April to September is the dry season and is genuinely pleasant, with days of 25 to 32°C and cool nights. Occasionally a surazo — a cold front driving up from Patagonia across the flat plain with nothing to stop it — drops the temperature by twenty degrees within hours, and frost is possible.
Rain
Falls almost entirely in summer, and decreases sharply from east to west: over 1,200 millimetres near the river, under 400 in the far north-west. It is also unreliable from year to year, which is what makes ranching here marginal.
Effect on travel
Wet season rain turns the region’s clay roads into an impassable surface locals call jabon — soap — and vehicles simply stop. Nothing beyond the paved highway is dependable between October and April.
Living with no water
The colonies were built around catching every drop off a roof into brick tanks, and that architecture is still visible: wide gutters, cisterns beside every house and communal reservoirs called tajamares dug to hold the wet-season runoff. A pipeline from the Paraguay river now supplies the central colonies, but outside them, roof catchment and trucked water remain how people live.
Dust and wind
The dry season brings dust and strong north winds ahead of fronts.