precipitation · Kenya
Nairobi
March–May long-rains total
Modelled demonstration series · not observed data
Failed long rains are the leading indicator for food insecurity across the Horn of Africa, and they fail in runs rather than singly. This chart's value is not the depth of one bad year but the frequency of bad years in the recent stretch. Pastoralists lose herds to consecutive failures, not to one.
75 years, modelled
Same reading, two normals
| Normal | Mean | σ | Pct | Return |
|---|---|---|---|---|
| 1951–1980 | 255 mm | −1.60σ | 5th | 1 in 18 years |
| 1991–2020 | 254 mm | −1.76σ | 4th | 1 in 26 years |
Today would rank 2 of 76 for lowest value in the modelled series. Nothing about the reading changes between rows — only the yardstick.
The season here
East Africa has two wet seasons. The long rains of March to May are the important one — they set the main planting season for the region.
Where this series comes from
MODELLED SERIES — not observed. Parameters set from published Nairobi long-rains climatology and the documented recent drying of the East African long rains; lognormal transform applied. The 75 annual values are synthesised by the seeded generator.
Every number on this page comes from a modelled series: 75 annual values synthesised by a seeded generator from published climatological parameters for Nairobi. It shows how anomaly reasoning works. It is not a measurement and must not be cited as one.
How to read σ
σ counts standard deviations from this place's own normal. The sigma guide · return periods.
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