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Rain going missing

What Is a Drought?

A drought is not just no rain — it is much less rain than a place is built around.

A dry place Little rain, but normalfor thereA drought Far less rain thanusual — everything isbuilt wrong for it
Drought is about the shortfall, not the total.

  1. Step 1 of 5

    Drought is relative, not absolute.

    Rainforest normal2,000 mm a yearRainforest in droughtstill far morethan a desert —but a disasterDesert normal50 mm — andperfectly fine

    A desert getting its usual 5 cm of rain is fine. A rainforest getting 5 cm would be a catastrophe. Drought means much less than normal for that place.

  2. Step 2 of 5

    Rain-bearing weather simply stops arriving.

    Low pressure Air rises, clouds form,it rainsHigh pressure parked Air sinks, no clouds,no rain

    A stubborn area of high pressure can park over a region for weeks, pushing air downward. Sinking air does not form clouds, so no rain falls.

  3. Step 3 of 5

    The ground dries from the top down.

    Soil moisture — gone inweeksfirst to failRivers and reservoirs —monthssecondDeep groundwater — yearslast, andslowest torecover

    Soil moisture goes first, then streams, then reservoirs, then deep groundwater. Each stage takes longer to empty — and much longer to refill.

  4. Step 4 of 5

    Dry ground makes itself drier.

    No rain Plants wilt Less moisture into the air Even lessrainSelf-feeding

    Plants normally release water into the air, which helps make rain. Once they wilt, that moisture stops, and the drought reinforces itself.

  5. Step 5 of 5

    Recovery needs steady rain, not a downpour.

    Downpour on hard ground Runs off — little soaksinSteady gentle rain Soaks down andrecharges

    Hard rain on baked ground runs straight off. Gentle rain over days soaks in. One dramatic storm can end a heatwave without ending a drought.

    Long droughts can lower the ground itself, as emptied aquifers compact and the land above sinks permanently.

The short version

A drought is a long shortfall against normal rainfall, and dry ground makes the shortfall worse.

Try it yourself

Pour water on dry compacted soil and on damp soil. The dry one repels it — which is why droughts are hard to break.

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