Extreme rainfall
How much rain is exceeded only once every 10, 50 or 100 years on average? Frequency analysis of extreme rainfall in each region, from 35 seasons (September to August).
102.7 mm daily rainfall record since 1991: Souss-Massa
Updated : 23 October 2026
In brief
What this means A '50-year' rainfall does not come back exactly every 50 years: it is a depth with a 2% chance of being exceeded each year. Values are computed from the ERA5 reanalysis, which smooths intense rainfall: they are for comparing regions and monitoring risk, not for designing structures in place of rain gauges.
1 Daily rainfall by return period
- Souss-Massa118.0 mm record 102.7 mm
- Tanger-Tetouan-Al Hoceima88.2 mm record 91.1 mm
- Rabat-Sale-Kenitra77.7 mm record 64.4 mm
- Oriental67.5 mm record 75.6 mm
- Dakhla-Oued Ed-Dahab64.8 mm record 74.1 mm
- Beni Mellal-Khenifra60.7 mm record 62.7 mm
- Draa-Tafilalet57.9 mm record 70.0 mm
- Fez-Meknes55.7 mm record 60.9 mm
- Casablanca-Settat53.2 mm record 58.1 mm
- Marrakesh-Safi46.2 mm record 59.5 mm
- Laayoune-Sakia El Hamra45.7 mm record 53.8 mm
- Guelmim-Oued Noun43.7 mm record 55.7 mm
Click a region to open its detailed analysis below.
2 The 2025-26 season in history
What this means At 5 of 12 points, the 30-day rainfall total of the 2025-26 season is the highest since 1991-92. River floods often come from repeated rain over several weeks rather than a single day: a season can therefore be a record over 30 days without being one over a single day.
| Point | 1 day | 10 days | 30 days |
|---|---|---|---|
| Tanger-Tetouan-Al Hoceima | 60.2 mmrank 5/35 | 242.3 mmrank 1/35 | 505.6 mmrank 1/35 |
| Oriental | 24.8 mmrank 22/35 | 51.8 mmrank 27/35 | 108.4 mmrank 14/35 |
| Fez-Meknes | 30.3 mmrank 20/35 | 111.2 mmrank 6/35 | 239.0 mmrank 1/35 |
| Rabat-Sale-Kenitra | 58.0 mmrank 4/35 | 164.2 mmrank 1/35 | 283.8 mmrank 1/35 |
| Beni Mellal-Khenifra | 62.7 mmrank 1/35 | 193.9 mmrank 1/35 | 351.5 mmrank 1/35 |
| Casablanca-Settat | 50.2 mmrank 3/35 | 104.2 mmrank 6/35 | 214.2 mmrank 3/35 |
| Marrakesh-Safi | 50.7 mmrank 2/35 | 148.4 mmrank 1/35 | 267.3 mmrank 1/35 |
| Draa-Tafilalet | 31.3 mmrank 5/35 | 53.3 mmrank 7/35 | 66.4 mmrank 7/35 |
| Souss-Massa | 54.9 mmrank 9/35 | 117.9 mmrank 12/35 | 157.4 mmrank 8/35 |
| Guelmim-Oued Noun | 17.5 mmrank 19/35 | 49.5 mmrank 6/35 | 73.3 mmrank 9/35 |
| Laayoune-Sakia El Hamra | 6.2 mmrank 24/35 | 8.2 mmrank 28/35 | 17.0 mmrank 18/35 |
| Dakhla-Oued Ed-Dahab | 20.7 mmrank 11/35 | 22.3 mmrank 12/35 | 25.4 mmrank 13/35 |
Rank 1 = highest value of all seasons since 1991-92 (red); ranks 2 and 3 in orange. Basin points are placed at flood-exposed towns, such as Ksar El Kebir on the Loukkos river.
3 Detailed analysis by region or basin
The series: maximum of each season (September to August)
Atypical values (beyond the box threshold) are shown in orange and are not removed: in a homogeneous reanalysis such as ERA5 they usually reflect a real event.
Return periods: fitted distributions and observed values
Distribution comparison
| Distribution | AIC | BIC | 100 years (mm) |
|---|---|---|---|
| Log-normal · selected | 294.4 | 297.5 | 97.8 |
| Gumbel | 294.6 | 297.7 | 97.2 |
| Log-Pearson III | 295.8 | 300.4 | 87.8 |
| GEV | 296.2 | 300.9 | 88.7 |
The selected distribution has the lowest AIC. BIC penalises the number of parameters more.
Rainfall depths by return period
| Return period | Rain (mm) | 90% CI |
|---|---|---|
| 2 years | 40.6 | 36.9 – 45.5 |
| 5 years | 55.8 | 50.0 – 61.4 |
| 10 years | 65.9 | 58.2 – 73.1 |
| 25 years | 78.7 | 68.9 – 89.8 |
| 50 years | 88.2 | 76.1 – 101.9 |
| 100 years | 97.8 | 83.3 – 114.0 |
Interval from resampling (200 draws), for the 1-day and 30-day durations. Its width at 100 years reflects the limited series length.
4 Intensity-duration-frequency (IDF) curves
IDF curves need hourly data. They are downloaded in stages during daily updates; the curves will appear automatically once at least 20 years are available.
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Intensity = maximum depth over the duration divided by the number of hours, for each return period, using the Gumbel distribution for all durations (1 to 24 hours) so the curves stay consistent.
Method and limits
- Data: daily and hourly rainfall totals from the Open-Meteo historical archive (ERA5 reanalysis), at each regional capital and at one point per major river basin, complete seasons only.
- Series: largest total over 1, 2, 3 and 5 consecutive days each year (and 1 to 24 hours for hourly data).
- Distributions: Gumbel, GEV, log-normal and log-Pearson III, fitted by maximum likelihood; GEV is discarded if its shape parameter exceeds 0.5 in absolute value.
- Length: about 35 years. A common rule allows extrapolation to about three times the series length: 100-year values remain the most uncertain.
- Trend: Kendall test on the annual daily maximum; a significant trend questions the stationarity assumption.
- Limits: ERA5 is a grid of about 30 km that smooths local intense rainfall, and values refer to one point per region. These results do not replace station measurements for designing structures.