Reservoir Watch

In the three months to 1 October 2026, 10.9% of Thailand received much less rain than is normal for the season, and 2.2% extremely little, a shortfall seen about one year in forty. 2 of the 35 reservoir sites we track are in that rain-short area. The 35 reservoirs were 84.1% full on their latest readings.

“Much less rain than normal” means the last three months were drier than about five in six of the same seasons on record at that point; “extremely little” drier than about thirty-nine in forty. The measure is the Copernicus Global Drought Observatory's three-month Standardized Precipitation Index (SPI-3), on a 25 km grid; the first threshold is roughly where the U.S. Drought Monitor starts D1 (moderate drought), so this headline reads like the Monitor's, though the Monitor also weighs soil moisture, streamflow and local reports. Area shares count the grid cells inside the country outline, weighted by latitude. All of it describes conditions on the ground, not how much water is stored; a reservoir can be full after a dry season and low after a wet one. Source: drought.emergency.copernicus.eu. European Drought Observatory / Global Drought Observatory, https://drought.emergency.copernicus.eu © European Commission – JRC. Licensed CC BY 4.0.