Aruba's geography: a dry island that drinks the sea

Where Aruba sits on the South American shelf

Aruba lies on the continental shelf of South America together with Bonaire, Curaçao and Trinidad and Tobago, so geologists place it entirely in South America although it is counted politically as a Caribbean island. It is the westernmost of the ABC islands and of the Leeward Antilles, and the westernmost island of the Aruba-La Blanquilla chain of small islands and atolls along the Venezuelan border. It sits on the boundary between the South American and Caribbean plates, in a system of faults along which the Caribbean plate moves westward relative to South America.

The distances depend on the source. The Wikipedia article on Aruba gives 29 kilometres to the Paraguaná peninsula and 77 kilometres west of Curaçao, while the article on its geography gives 25 kilometres to the Venezuelan coast and 68 kilometres to Curaçao. Britannica, and the opening of the Wikipedia article on Aruba, put the island 80 kilometres north-west of Curaçao.

The area is just as unsettled. The country's record carries 179 square kilometres, Britannica and the IMF's table of basic data for 2024 give 180, and the Wikipedia article on the island's geography gives a total of 193 with a coastline of 68.5 kilometres. None of the sources says what the extra area in the largest figure includes. The island measures 32 kilometres from its north-western to its south-eastern end and 10 kilometres at its widest point.

How three kinds of rock divide the island

Aruba is mostly low, flat to gently rolling ground with a few isolated hills, and three bodies of rock account for almost all of it.

The lava formation is the oldest rock visible on the island, dated to the Turonian by ammonite imprints, and it was baked by the intrusion of the batholith. The batholith weathers into the rounded diorite boulders that stand in piles at Ayo and Casibari, and into Hooiberg, a conical hill of 165 metres by the Wikipedia figure and 171 by Britannica's, which looks taller than it is because the ground around it is so flat.

The high point is Jamanota, which the record gives as 188 metres and Britannica as 189. Arikok, beside it, reaches 186 metres. Both stand in the lava formation, where faults control a set of valleys running east to west.

The terraces record a slow rise. The lower one, 5 to 10 metres above the sea, is 30,000 to 129,000 years old, and the middle one, at 15 to 25 metres, is up to 510,000 years old, which gives an uplift rate of about 0.05 millimetres a year. Aruba stood above the sea in the Oligocene and went under it again in the middle Miocene.

Why the two coasts of Aruba look so different

The trade winds blow onto the north-east coast from the Atlantic almost without a break, and that coast is wave-cut coral limestone with deep water, rough seas and small sandy coves that Papiamento calls boca, a mouth. The terraces there have wide platforms and steep backslopes. The arid climate has preserved them well, since limestone resists weathering where there is little rain, and only a thin cover of drought-adapted scrub grows on them. The high plateaus on this side hold caves and small natural bridges.

The south-west coast is in the lee. Its terraces are narrower and gentler, its sea is calm, and a barrier reef lies about 370 metres offshore between Punta Brabo and Oranjestad, capped by a ridge of coral fragments and dropping on the seaward side to at least 46 metres. This is the coast of white sand beaches.

That difference decides where people and money are. The designated tourism zone, set up in the late 1980s, covers about 16% of the island's land, and most hotels, timeshares and apartments stand along the north-west coast. The Wikipedia article on Aruba's geography records resident concern about new building near the Bubali wetland on the west coast and new hotels on the east coast, including one at Seroe Colorado.

How much rain falls on Aruba

Aruba has a hot semi-arid climate, BSh in the Köppen classification, while most of the Caribbean is humid and tropical. The sources give the annual rainfall three ways: about 500 millimetres in the Wikipedia article on Aruba, about 430 millimetres in Britannica, and 18 inches, roughly 460 millimetres, from the Aruba Tourism Authority.

The average hides very large swings, most of them tied to the Southern Oscillation. In strong El Niño years, including 1911 to 1912, 1982 to 1983 and 1997 to 1998, rainfall has fallen to about 150 millimetres. In La Niña years such as 1933 to 1934, 1970 to 1971 and 2010 to 2011 it has passed 1,000 millimetres, with single months of 350 to 400 millimetres. What rain there is falls mostly in a short season, which Wikipedia dates from September to January, when the Intertropical Convergence Zone retreats south and moist north-easterly winds become more frequent. The tourism authority gives October to December.

Temperature barely moves. Mean monthly temperatures in Oranjestad run from 27.0 °C to 29.6 °C, and the constant north-easterly wind tempers the heat. Aruba lies south of the main development region for Atlantic hurricanes, and Britannica notes that one occasionally does reach it; late in the 2020 season the island was affected by two hurricanes in their early stages. Sea temperatures have risen by at least 1.3 °C since the 1950s, and the IMF counted sea level rise and extreme weather among the risks to the economy in its 2025 consultation.

How Aruba learned to drink the sea

Water was the island's limiting resource long before tourism. Stichting Monumentenfonds Aruba records that islanders drew from five or six wells, including Pos Grandi near Savaneta, the reservoir at Mangle Corá near Baby Beach and the spring at Fontein on the north coast, and carried the water home by donkey. Rain was stored in cisterns and in tankis, reservoirs behind small dams, which gave their names to places such as Tanki Flip and Tanki Leendert.

Desalination began around 1903 at the gold mining company, whose groundwater and rainwater could not supply the ore-processing works, and which took seawater from the Spanish Lagoon. When Lago arrived, it imported water from the United States in special tankers. The government water service built a desalination plant at Balashi from 1928 and opened it in 1932, piping water to Oranjestad and San Nicolaas from reservoirs about 50 metres up at Kibaima. In 1934, 454 homes were connected.

The technology changed several times. Multi-effect thermal distillation ran from 1932 to 1983, multi-stage flash evaporators came in from 1965, and demand still outran supply badly enough that drinking water was imported in 1982, 1983 and 1990 from the United States, Venezuela and Dominica. Reverse osmosis replaced the thermal plants in steps from 2008, and by 2015 the utility, WEB Aruba, produced its water entirely by that method. For most of its history the distilled water was run over a bed of crushed coral to put calcium back into it.

Power is tied to the same works. The Vader Piet wind park of 30 megawatts was completed at the end of 2009 and the Sunrise solar park at Lago Heights, of 7.5 megawatts, in 2018. A fourth engine plant of 102 megawatts, able to run on heavy fuel oil and later on natural gas, came into service in June 2022 and ended 64 years of thermal generation.

What grows and lives in the dry scrub

The vegetation is xeric scrub: cacti such as Melocactus and Opuntia, thorny shrubs, evergreens and drought-tolerant trees including Caesalpinia coriaria and Vachellia tortuosa, with most of the plant cover in the gullies and on the lee sides of hills. Wikipedia attributes the dryness partly to deforestation and grazing during the Spanish period, and records forest of 420 hectares in 2020, about 2% of the land and the same as in 1990, none of it primary forest.

The Aruba Conservation Foundation counts 34 endemic species on land and sea, and 282 species of bird recorded on the island. Among them are the Aruba Island rattlesnake, known as the cascabel, the Aruban whiptail lizard, the burrowing owl or shoco, the parakeet or prikichi, and Hummelinck's vesper mouse.

Introduced animals are the other half of the story. Goats and donkeys, brought in the early sixteenth century, graze the vegetation down. The first boa constrictor was found in 1999 and the species had spread across the whole island by 2005; a study published in 2021 of more than 500 captured boas found over 400 kinds of prey in their stomachs. Lionfish have reached the reefs, and cane toads live in irrigated gardens and hotel grounds.

How much of the island is protected

Arikok National Park was established by ministerial order in 2000, after plans going back to 1980 and a nature protection regulation in 1995. The Aruba Conservation Foundation, which runs it, gives its size as 34 square kilometres, and the Wikipedia article on the park gives 32; both put it at about a fifth of the island. It takes in Jamanota, the lava hills, Fontein Cave with its red pictographs, the old gold mines at Miralamar and the north coast between Daimari and Boca Prins.

The foundation manages nearly 25% of Aruba's land in all, together with four marine protected areas. The Spanish Lagoon, the Spaans Lagoen, has been a Ramsar wetland since 1980, and four more Ramsar sites have since been added. The Bubali Bird Sanctuary, a brackish lagoon, is the only other significant body of water with nature reserve status. Wikipedia cites a far lower figure of 0.5% of the land as protected in 2022, without saying what that definition counts.

Inside the park the pressures are grazing and driving. Goats, sheep and donkeys strip the vegetation and leave bare soil open to wind and water erosion, and studies of off-road driving cited by Wikipedia found dust coating plants more than 200 metres from the tracks, with a risk of desertification on the route between San Fuego and Conchi. Field surveys in the park recognise seven vegetation types, two of them found only on the limestone plateau in its southern part.

Where the people of Aruba live

Aruba has no administrative subdivisions. The Central Bureau of Statistics divides it for census purposes into eight regions and 55 zones: Noord and Tanki Leendert, Oranjestad West, Oranjestad East, Paradera, Santa Cruz, Savaneta, San Nicolas North and San Nicolas South. The 2020 census counted 108,166 people, 6,682 more than in 2010, and a density of 601 people per square kilometre, up from 564.

The regions differ in language as much as in size. In the 2020 census, San Nicolas South had the highest share of households speaking Papiamento and English at home, at 28.7%, in the old refinery district where a local English creole known as San Nicolaas English is spoken, while Oranjestad East had the highest share speaking Papiamento alone, at 56.6%. In San Nicolas South nearly a third of the population, 30.6%, reported that Papiamento was not one of the two languages most spoken at home, against 11.6% in Paradera, where 85.2% speak it at home alone or with another language. The population grew fast from the 1960s, first with refinery workers and then with the tourism industry.