Acre Summer Time (Historical)
UTC offset: -04:00 (historical, summer only)
Standard offset: -05:00 (ACT, current year-round)
IANA identifier: America/Rio_Branco
Abbreviation: ACST (no longer active)
DST status: Discontinued
Acre Summer Time was the daylight saving designation for Brazil's westernmost state, shifting clocks forward one hour from UTC-05:00 to UTC-04:00 during southern hemisphere summer. Brazil abolished DST nationwide in 2019, but Acre had already stopped participating years earlier. The state's equatorial location (around 8-11 degrees south) provides minimal daylight variation across seasons, making the practice largely pointless.
Acre itself has bounced between time zones repeatedly. From 2008 to 2013, the state moved from UTC-05:00 to UTC-04:00 (matching Manaus). In 2013, a popular referendum moved it back to UTC-05:00, where it remains. The DST layer on top of these shifts created years of scheduling confusion for a state of only 900,000 people.
Acre's Unusual History
This is a state that used to be part of Bolivia. During the rubber boom of the late 1800s, Brazilian rubber tappers flooded into the Acre territory. Tensions escalated into the Acre War (1899-1903), and Bolivia eventually ceded the territory to Brazil in the 1903 Treaty of Petropolis in exchange for financial compensation and a promise to build a railway (the Madeira-Mamore, which was completed but became obsolete almost immediately).
The rubber boom collapsed after 1910 when Southeast Asian plantations undercut Amazonian prices. Acre's economy contracted dramatically and never fully recovered. Today the state relies on cattle ranching, small-scale agriculture, government employment, and Brazil nut harvesting.
Rio Branco
Population about 420,000. The capital sits on the Acre River in dense tropical forest. The city is roughly 3,100 km from Brasilia and 1,500 km from Manaus. Isolation defines it. The only significant road connection (BR-364) links to Porto Velho in Rondonia and onward to the rest of Brazil. During the wet season, roads flood and sections become impassable.
Rio Branco has the Palacio Rio Branco (state government seat), the Rubber Museum (Museu da Borracha) documenting the boom era, and a riverfront market. The economy is modest: government services, some light industry, and commerce serving the surrounding agricultural areas.
Why DST Failed Here
At 10 degrees south latitude, Rio Branco's longest day is about 12 hours 35 minutes. The shortest is about 11 hours 25 minutes. That's barely over an hour of seasonal variation. Shifting the clock gains almost nothing. Meanwhile, the disruption of changing schedules in a region where many people work agricultural or extractive jobs tied to natural light was genuinely counterproductive.
Brazil's broader DST regime (which ran from the mid-1980s to 2019 in southeastern and southern states) made sense at higher latitudes like Sao Paulo (23.5S) or Porto Alegre (30S), where summer days are meaningfully longer. Applying it to equatorial states like Acre was always questionable.
The Amazon Context
Acre sits at the western edge of the Brazilian Amazon. About 87% of the state remains forested (one of the highest rates in Brazil). Chico Mendes, the rubber tapper and environmental activist assassinated in 1988, was from Xapuri in Acre. His murder brought international attention to Amazon deforestation and led to the creation of extractive reserves where traditional communities can harvest forest products sustainably.
The Chico Mendes Extractive Reserve covers 970,000 hectares and supports about 10,000 families who harvest rubber, Brazil nuts, and other forest products.
Indigenous Communities
Acre has significant indigenous populations, including the Ashaninka, Huni Kuin (Kaxinawa), Yawanawa, and others. About 15 indigenous territories cover roughly 14% of the state. These communities maintain traditional practices including ayahuasca ceremonies, which have attracted international attention and some controversy around cultural tourism.
Climate
Tropical/equatorial:
- Temperature: 24-32C year-round (minimal seasonal variation)
- Wet season: October-April (heavy rainfall, flooding)
- Dry season: May-September (still warm, less rain)
- Annual rainfall: 1,700-2,400 mm
Technical Identifiers
- America/Rio_Branco (IANA canonical)
- ACT (current, Acre Time, UTC-05:00)
- Windows: "SA Pacific Standard Time" (UTC-05:00 group)
- Historical: -05:00 standard / -04:00 summer (when DST was observed)
- Brazil abolished all DST in 2019
Quick Reference
| Attribute | Value |
|---|---|
| Historical summer offset | -04:00 |
| Current UTC offset | -05:00 (permanent) |
| DST status | Abolished |
| IANA zone | America/Rio_Branco |
| State population | ~900,000 |
| Capital | Rio Branco (~420,000) |
| Latitude | ~8-11S |
| Key history | Rubber boom, Chico Mendes |
| Forest cover | ~87% |