How Korea grades a drought — three scales, one word 'severe'

When a Korean news report says a region is at the "severe" drought stage, it is genuinely hard to know what has been asserted. There is a reason. Korea classifies drought as three separate things, and the three use different measurements.

The stage names are identical: attention → caution → alert → severe. The rulers are not.

1. Three droughts

There is a sequence. Rain fails (meteorological) → reservoirs empty (agricultural) → tap water comes under threat (municipal). So a region can be at alert on the meteorological scale and normal on the municipal one, or the reverse. Groundwater and the wide-area mains network act as buffers between the stages.

2. Agricultural drought — reservoir level against the norm

This is the criterion that appears most often in news coverage.

The most common misreading: **a reservoir level of 40% is not "severe." Forty per cent of the seasonal norm is.**

Suppose a region's reservoirs sit at 34.1% in August. That figure alone does not determine a stage; you need the seasonal norm. If the norm is 71.3%, the ratio is 47.8% — inside the alert band. Had the norm been 85%, the same 34.1% would compute to 40.1% and sit on the edge of severe.

Why ratio rather than absolute level. Reservoirs differ in size and catchment, so their ordinary August levels differ — some sit in the 50s, others in the 80s. Ranking by absolute level would flag the naturally low ones permanently. The system asks instead how far below its own normal a place has fallen.

3. Meteorological drought — six months of rainfall

Two features stand out.

① The window is six months. One dry month does not produce a meteorological drought, because groundwater and reservoirs are filled by half a year of accumulated rainfall. A year with a dry spring therefore recovers poorly even when summer storms arrive.

② Only 'severe' has a different shape. Attention, caution and alert are set by a single rainfall percentage; severe adds duration and a damage outlook, because it denotes a state requiring national-level response.

The Standardised Precipitation Index (SPI) is also used, normalising rainfall against a region's own distribution — -1.0 or below indicates dry conditions. The six-month version, SPI6, is the baseline monitoring index.

4. Municipal and industrial drought — no single percentage

This is the hardest of the three to summarise, because there is no single percentage threshold.

The method: assemble the available water resources — dam storage, river flow, precipitation — and compare them against the region's water demand to judge whether normal supply is feasible. The same storage volume therefore escalates faster in a region with larger population and industrial draw.

The logic is sound. Household water comes from a combination of sources rather than one reservoir, and the wide-area mains network can move water between regions.

The cost is that there is no number a news report can quote. Agricultural drought reports cleanly as "reservoirs at 34.1%." Municipal drought arrives instead as individual dam figures — "the dam has fallen to 31.8%, entering the alert stage." This article could not confirm the quantitative stage thresholds in official documents.

5. Rationing is not tied to the stage

The most practical misconception sits here. "Alert" does not mean the taps stop.

Supply restrictions are decided by local governments based on actual source conditions, which is why outcomes diverge within a single municipality.

The 26 areas placed on restricted supply in South Gyeongsang in August 2026 had exactly this composition — six island communities without mains connections and 20 villages on small-scale systems. Urban mains supply continued largely normally over the same period. The situation is set out in "Gyeongnam drought: reservoirs at 34.1%."

6. A national fire mobilisation is not a drought stage

One further confusion worth clearing. The national fire-service mobilisation order that appears in drought coverage sits outside the stage system entirely.

It is an order directing fire capability nationwide into one region when local resources cannot cope, normally used for large fires or major disasters. In a drought it becomes a means of hauling water. It is not triggered automatically by the severe stage; it is triggered when there are not enough vehicles locally to carry water.

7. What is still open

Quantitative thresholds for municipal and industrial drought could not be confirmed. This article describes only the method.

The meteorological 'severe' criteria were not checked against the original notice. They were assembled from press material.

Whether reservoir management authority changes how criteria apply is unconfirmed. Some reservoirs are managed by the national rural corporation and others by municipalities, and if the statistical coverage differs, the same region's level differs by source. In August 2026 the South Gyeongsang provincial average was reported as both 34.1% and 32.8%, and the cause of that gap was not established.

Other disaster-metric frameworks are set out in "How strong is a magnitude 7.4 earthquake" and "Korea's three-tier heat alert system."