WhatAWeatherRainfall drought index by city
Accumulated rainfall versus what would be normal (1991-2020 average) for the same dates.
Last 12 months
Last 6 months
Last 3 months
Annual precipitation: 30 years of history
Annual precipitation total (mm) and the 1991-2020 average. Clearly dry years are shown in orange.
Precipitation anomaly map (last 12 months)
18 provincial capitals analysed against their 1991-2020 normal. The calculation takes a few seconds the first time; afterwards it is cached for 12 hours.
The Canary Islands (Las Palmas and Santa Cruz de Tenerife) appear in the pills and on the map by panning the view to the south-west. The circles use the same colour scale as the rest of the tool.
Hydrological drought: reservoirs by basin
Fill percentage of the stored water reserve by river basin district.
See the reservoir-by-reservoir detail in our Spain reservoirs section. Official weekly data: embalses.net and the MITECO Hydrological Bulletin.
Methodology: how we measure drought
This monitor calculates a rainfall index: the precipitation accumulated over the last 3, 6 and 12 months divided by the average precipitation for those same calendar dates during the 1991-2020 reference period, the climatological standard of the World Meteorological Organization. The result is expressed as "% of normal": 100 % means exactly normal rainfall; 50 % means only half the usual rain has fallen.
| Level | % of normal | Interpretation |
|---|---|---|
| Normal | ≥ 90 % | No significant precipitation deficit; above 110 % the period is wet. |
| Mild drought | 70 – 90 % | Noticeable deficit; watch rain-fed crops and basin headwaters. |
| Moderate drought | 50 – 70 % | Significant, persistent deficit; likely impact on agriculture and reserves. |
| Severe drought | < 50 % | Less than half the normal rainfall; exceptional situation. |
Data source and limits of the method
Daily precipitation comes from the ERA5 reanalysis of the European Centre (ECMWF), served by the Open-Meteo archive API at a resolution of roughly 9-25 km. A reanalysis interpolates observations and model output, so in mountainous or coastal areas the point value may differ from the nearest rain gauge.
This indicator is not the SPI (Standardised Precipitation Index) used by AEMET, nor an official product: the SPI statistically normalises the rainfall distribution, whereas here we show the direct ratio to normal, which is easier to interpret. Both usually agree on the overall diagnosis, but official drought declarations belong to AEMET and the river basin authorities of MITECO.
Meteorological versus hydrological drought
Meteorological drought is the lack of precipitation; hydrological drought is the scarcity of stored or flowing water and arrives with months of delay, shaped by consumption and management. That is why we combine the rainfall index with the fill percentage of the reservoirs by basin: reading them together gives the full picture. For the official reservoir-by-reservoir figure, check embalses.net or MITECO's weekly bulletin.
Frequently asked questions
What does the percentage of normal mean?
It compares the rain accumulated over a period (last 3, 6 or 12 months) with the average for those same calendar dates during 1991-2020. 100 % is normal rainfall; 60 % means only 60 % of the usual rain has fallen. We classify: ≥90 % normal, 70-90 % mild drought, 50-70 % moderate and <50 % severe.
Is this the official AEMET SPI index?
No. It is a simple rainfall index (percentage relative to the 1991-2020 normal) calculated with the ERA5 reanalysis via Open-Meteo. It does not replace the SPI or the official products of AEMET or MITECO, although it usually points in the same direction.
How often is the data updated?
The Open-Meteo ERA5 archive is updated daily with a lag of a few days, so the calculations normally reach yesterday or the day before. Reservoirs are updated with the weekly data from our reservoirs section.
Can there be a drought with full reservoirs, or the other way round?
Yes. Reservoirs respond with months of delay and depend on management and consumption; a basin can receive water from rainy headwaters even if the lowlands are dry. That is why we show precipitation and stored water separately.