The Long Swell

Southern Peru and the Altiplano · 15 to 28 August 2026 · published 30 August 2026

12.3 mm of rain fell over Southern Peru and the Altiplano in 15 to 28 August 2026, the 4th highest of 27 years of the same fortnight.

Whether this rainfall caused flooding has not been established. No South American gauge checked. GloFAS discharge is the intended corroboration and is blocked on a licence acceptance. Our own instruments measure rainfall and flood extent, and neither can answer it.

Southern Peru and the Altiplano recorded 12.3 mm over 15 to 28 August 2026, against a median of 3.4 mm for the same fortnight since 2000. That is the 4th highest of the 27 years compared. No multiple is given: the usual total here is small enough that a ratio against it would measure noise rather than how unusual the fortnight was. This measures RAINFALL, not flooding.

What was measured, and what was not
RainfallGPM IMERG Late Run v0712.3 mm4 of 27
Rainfall intensityone day carried 32% of the fortnight, against a 23% medianno concentration
Flood extentNASA MODIS MCDWD 3-Day compositenot assessed
no flood-extent baseline has been built for this region, so the instrument's ability to see it is unknown and untested
12.3 mm

against a typical 3.4 mm for this fortnight

Rainfall over 15 to 28 August 2026, by year

12.3 mm20262000200120043 of 26 fortnights in this record sit above it.RAINFALL, 15 TO 28 AUGUST 2026 · MM · ONE SLOT PER YEAR attribution pending

What this is

Rainfall accumulated over 15 to 28 August 2026 and compared with the same calendar fortnight in each of the previous 26 years, as an area mean over the region. 14 of 14 days are compared; no days were excluded from EVERY year, not just this one, so the comparison stays like for like.

What this is not

Not a measurement of flooding. We have not measured flooding here. This page reports rainfall only. Flood extent is not assessed for European regions: the screen passed none of the six tested, because week-to-week satellite visibility varies enough that a ranking would rank the weather over the sensor. That is a limit we measured, not one we assumed.

Source. GPM IMERG Late Run v07, rainfall, NOT flooding. As of 28 August 2026.