Saudi rainfall over 45 water years (1981/82–2025/26): totals, trend, season and drought years per governorate

A 45-water-year series (September to August) for each of the 147 governorates: rainfall each year, the median, driest and wettest year, the wettest month and each season share, the rainfall regime (winter, spring or summer), the standardised precipitation index, the number of drought years, and a rank-based trend test, plus mean rainfall cells and two long tables ready for charting.

The area-weighted national mean is 102.6 mm a year.

Who it is for

Geography and meteorology departments, water and dam engineers, agriculture and rangeland research, emergency management, researchers and postgraduate students.

Method: what we add to the raw data

• The water year runs September to August rather than the calendar year, so it splits neither the northern winter rains nor the south-western summer rains; year 2025/26 means September 2025 to August 2026.
• Monthly rainfall was taken from an open global source at 0.05 degree cells (about 5 km), and both an annual and a monthly cube were built per cell.
• Cell values were averaged inside each governorate; governorates smaller than a cell take the value of the cell they sit in, so none is left without a figure.
• The rainfall regime comes from each month averaged across all years: the seasonal shares are summed and the regime named after the highest.
• Trend uses the Mann-Kendall rank test with a Theil-Sen slope in mm per decade, and is only called a trend when the p-value falls below 0.1.
• The standardised precipitation index is computed per year from a gamma distribution fitted to each governorate own years; a drought year is one at -1 or below.

Product details

Spatial layers

• governorates_rainfall — polygons, 121: Governorates with rainfall, regime and trend

Raster files (GeoTIFF)

• D117_mean_annual_mm.tif — 446 × 346, about 5 km: Mean annual rainfall
• D117_median_annual_mm.tif — 446 × 346, about 5 km: Median annual rainfall

Tables

• D117_governorates_rainfall.csv — 121 rows: Rainfall, regime and trend per governorate
• D117_year_by_governorate.csv — 5,445 rows: Long table: each water year by governorate
• D117_monthly_by_governorate.csv — 1,452 rows: Mean of each month per governorate
• D117_national_by_year.csv — 45 rows: National mean per water year

Limitations

• The source cell is about 5 km, so fine mountain detail in the Sarawat is not represented and small governorates share a cell.
• The source blends satellite and station estimates; it suits comparison and trend, not a report on a specific station.
• Desert rainfall arrives in a few highly variable showers, so an annual mean means less there than in the south-west.
• The latest year may be incomplete if its months are not yet all present in the source.
• The standardised index compares a governorate with itself, not with others: -1 in Jazan is not the same amount as -1 in Al Jawf.
• The p-value is the probability of a slope this large or larger if there were no trend at all, not the probability that the trend is chance.

FAQ

How long does delivery take?

Up to 6 hours after payment is confirmed.

How long does the download link last?

24 hours, and it is renewed free on request.

Can I get a refund?

Digital products are not refundable once downloaded — unless the file is defective or does not match the description, in which case it is replaced or fully refunded.

What does the licence allow?

Commercial use is allowed for you and the organisation you buy for; resale or redistribution is not.