The Precipitation -- Rainfall indicator measures the percentage variation of rainfall (liquid precipitation only, excluding snow) compared to the 1961--1990 WMO climatological reference period. Precipitation is a fundamental parameter of local microclimate: it influences water availability for vegetation, groundwater recharge, soil erosion, and biological cycles of pollinators and other organisms.
The KPI compares the mean annual precipitation of the last three years with the historical baseline (1961--1990), providing a synthetic measure of rainfall anomaly. Additional comparisons with the previous three-year period, 10 years ago, and 50 years ago help contextualise the trend over medium and long term.
Significant variations in precipitation -- both in excess and deficit -- can alter habitats, modify plant community composition, affect flowering phenology, and compromise resource availability for pollinators.
Distinction from Precipitation Variation (rain_kpi): This KPI (rain) tracks liquid precipitation only (rainfall), whereas the related Precipitation Variation KPI tracks total precipitation (rain + snow). The calculation methodology is identical, but the input data is filtered to exclude snowfall.
Data come from the Open-Meteo Historical Weather API, based on meteorological reanalysis models (ERA5, ERA5-Land) with global coverage from 1940 to present.
For each site, the annual rainfall time series is extracted from the geographic position of the site centroid.
The primary delta is computed as:
Formula: Rainfall Variation = 100 x (Mean last 3 years - Reference mean 1961-1990) / Reference mean 1961-1990
Three additional multi-window comparisons are computed identically:
Formula (multi-window): Delta vs 3y = 100 x (Mean last 3 years - Mean 3 years ago triennium) / Mean 3 years ago triennium Delta vs 10y = 100 x (Mean last 3 years - Mean 10 years ago triennium) / Mean 10 years ago triennium Delta vs 50y = 100 x (Mean last 3 years - Mean 50 years ago triennium) / Mean 50 years ago triennium
Absolute precipitation for the most recent year:
Formula (absolute): Absolute rainfall = Most recent annual rainfall / 10 (mm to cm conversion)
Unit: Percentage (%) for delta values; centimetres (cm) for absolute annual precipitation.
Note: Precipitation values are aggregated as annual sums, not annual means. This is consistent with standard climatological practice for rainfall data.
Baseline: The WMO standard 1961--1990 climatological reference period.
| Source | Provider | Coverage | Resolution | Period |
|---|---|---|---|---|
| Open-Meteo Historical Weather (ERA5-Land) | Open-Meteo | Global | ~10 km | 1940-01-01 -- present |
Gauge. A semicircular arc gauge displaying the site's rainfall delta relative to the 1961--1990 baseline, color-coded by quality grade and supplemented by three temporal comparison rows.
Purpose: Answers the question "How does the site's current rainfall compare to the long-term baseline, and is the trend improving or deteriorating across recent time windows?"
Description: The component is divided into two panels side by side. The left panel shows three delta comparison rows -- change vs. 3 years ago, vs. 10 years ago, and vs. 50 years ago -- each with a colored badge showing the delta percentage. Below the rows is a site score badge showing the main delta in an A--E grade. The right panel contains the circular arc gauge with colored quality sectors. The current rainfall delta is shown in large text at the center (e.g., "+38.3 %"). A data source badge ("Open-Meteo") and a tooltip with the full legend are accessible from the card header.
How it's calculated: The gauge center value is the rainfall variation delta: the 3-year mean annual rainfall minus the 1961--1990 baseline mean, expressed as a percentage. The arc position and badge color are determined by the quality grade ranges. Each delta row compares the current 3-year mean against the triennium centered 3, 10, or 50 years ago.
Legend:
| Level | Range | Color | Meaning |
|---|---|---|---|
| A (Excellent) | High rainfall | ■ #00A67A | Rainfall well above historical average |
| B (Good) | Above-normal | ■ #00DF80 | Above-normal rainfall |
| C (Moderate) | Near-normal | ■ #FFD21E | Rainfall near the historical baseline |
| D (Poor) | Below-normal | ■ #FF8B16 | Below-normal rainfall |
| E (Critical) | Very low | ■ #FF367F | Very low rainfall; drought stress likely |
Interpretation example: If the gauge shows "+25.4 %" (grade B, green) with delta rows of +18.2 % vs. 3 years, +30.1 % vs. 10 years, and +35.7 % vs. 50 years, the site is receiving substantially more rainfall than the long-term baseline, with a consistent positive trend across all time windows -- a sign of improving water availability and reduced drought stress for local ecosystems.
Line Chart. A horizontally scrollable area chart showing annual total rainfall for every year in the historical record, with an optional toggle to display future climate scenario projections.
Purpose: Answers the question "How has total annual rainfall at this site evolved year by year, and what do climate models project for the coming decades?"
Description: The chart displays a blue area line where each point represents one year's total annual rainfall (in cm). The X axis shows years; the Y axis shows rainfall in cm. A "Past / Future" toggle at the top of the card switches between historical data and a selected climate scenario projection. When the Future view is active, the historical line continues and a dashed blue line extends into the projected years; a scenario dropdown (SSP1-2.6, SSP2-4.5, SSP5-8.5) allows selecting the scenario. For future data points, the tooltip shows a "+/- X.X cm" uncertainty range. Hovering any data point shows the year, absolute rainfall in cm, and the delta relative to the 1961--1990 reference average.
How it's calculated: Each point represents the annual sum of rainfall for that year, converted from mm to cm (/ 10). The reference average is computed as the mean of data points falling in the 1961--1990 window. The tooltip delta is: current year value - 1961--1990 mean. Future scenario values come from downscaled climate model ensembles.
Interpretation example: If the chart shows a generally stable trend hovering around 80 cm from 1960 to 2000, then a gradual rise to ~95 cm by 2020, the site's rainfall has been increasing in recent decades relative to its historical norm -- consistent with a positive delta in the Gauge element.
Zippenfenig, P. (2023). Open-Meteo.com Weather API. Zenodo. DOI: 10.5281/zenodo.7970649.
Hersbach, H., Bell, B., Berrisford, P., Hirahara, S., Horanyi, A., Munoz-Sabater, J., Nicolas, J., Peubey, C., Radu, R., Schepers, D., Simmons, A., Soci, C., Abdalla, S., Abellan, X., Balsamo, G., Bechtold, P., Biavati, G., Bidlot, J., Bonavita, M., De Chiara, G., Dahlgren, P., Dee, D., Diamantakis, M., Dragani, R., Flemming, J., Forbes, R., Fuentes, M., Geer, A., Haimberger, L., Healy, S., Hogan, R. J., Holm, E., Janiskova, M., Keeley, S., Laloyaux, P., Lopez, P., Lupu, C., Radnoti, G., de Rosnay, P., Rozum, I., Vamborg, F., Villaume, S., and Thepaut, J.-N. (2020). The ERA5 global reanalysis. Quarterly Journal of the Royal Meteorological Society, 146(730), 1999--2049.
Munoz Sabater, J., et al. (2021). ERA5-Land: a state-of-the-art global reanalysis dataset for land applications. Earth System Science Data, 13(9), 4349--4383. DOI: 10.5194/essd-13-4349-2021.
See the Calculation Methodology section for the core computation. Additional processing details are documented here for expert users.