The Precipitation Variation KPI measures the percentage change in annual precipitation at a monitored site relative to the 1961--1990 WMO climatological baseline. It compares the mean of the last three years of annual rainfall against the 30-year reference average, expressing the result as a signed percentage. Three additional multi-window comparisons (vs. 3, 10, and 50 years ago) complete the picture.
This is a direct indicator: a positive value means precipitation is at or above the baseline, which is ecologically favourable. Healthy rainfall levels sustain vegetation, reduce drought stress, and support soil moisture and biodiversity.
The absolute annual precipitation for the most recent year is also stored (in centimetres) and can be displayed alongside the delta.
ESRS alignment: E1 (Climate change), E3 (Water and marine resources).
The primary delta is computed as the percentage difference between the recent 3-year mean and the 1961--1990 reference mean:
where the reference mean is the average of annual precipitation sums over the WMO standard 1961--1990 period.
Three additional multi-window comparisons are computed identically, replacing the reference mean with the triennium centred 3, 10, or 50 years ago:
Absolute precipitation for the most recent year is expressed in centimetres (annual sum in mm divided by 10).
Precipitation values are aggregated as annual sums, not annual means. This is consistent with standard climatological practice for rainfall data.
Data are sourced from Open-Meteo Historical Weather (ERA5-Land) at approximately 10 km resolution, covering the period from 1940 to present.
Gauge. A semicircular arc gauge displaying the site's precipitation delta relative to the 1961--1990 baseline, colour-coded by quality grade and supplemented by three temporal comparison rows.
Purpose: 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 coloured badge showing the delta percentage (e.g., "+32.7 %", "+43.6 %", "+48.7 %"). 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 coloured quality sectors. The current precipitation delta is shown in large text at the centre (e.g., "+38.3 %"). A data source badge ("Open-Meteo") and a tooltip with the full legend are accessible from the card header.
130Precipitation (cm)
How it's calculated: The gauge centre value is the 3-year mean annual precipitation minus the 1961--1990 baseline mean, expressed as a percentage. The arc position and badge colour are determined by mapping the absolute precipitation value (in cm) to the quality ranges. Each delta row compares the current 3-year mean against the triennium centred 3, 10, or 50 years ago.
Legend:
| Level | Range (cm absolute) | Color | Meaning |
|---|---|---|---|
| A (Excellent) | 160 -- 200 | ■ #00A67A | High precipitation; well above average |
| B (Good) | 120 -- 160 | ■ #00DF80 | Above-normal precipitation |
| C (Moderate) | 80 -- 120 | ■ #FFD21E | Near-normal precipitation |
| D (Poor) | 60 -- 80 | ■ #FF8B16 | Below-normal precipitation |
| E (Critical) | 0 -- 60 | ■ #FF367F | Very low precipitation; drought stress likely |
Interpretation example:
If the gauge shows "+38.3 %" (grade B, green) with delta rows of +32.7 % vs. 3 years, +43.6 % vs. 10 years, and +48.7 % 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.
Line Chart. A horizontally scrollable area chart showing annual total precipitation for every year in the historical record, with an optional toggle to display future climate scenario projections.
Purpose: 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 precipitation (in cm). The X axis shows years; the Y axis shows precipitation 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 "plus/minus" uncertainty range. Hovering any data point shows the year, absolute precipitation in cm, and the delta relative to the 1961--1990 reference average (e.g., "delta [1961--1990]: +12.5 cm"). Annual values are also shown as small labels directly on each data point.
How it's calculated: Each point represents the annual sum of precipitation for that year, converted from mm to cm (divided by 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 minus the 1961--1990 mean. Future scenario values come from climate model projections.
Interpretation example:
If the chart shows a generally rising trend from ~70 cm in 1960 to ~95 cm in 2020, with the 1961--1990 reference average around 75 cm, the site is receiving more rainfall than its historical norm -- consistent with the positive delta shown in the Gauge element.
| Source | Provider | Coverage | Resolution | Period |
|---|---|---|---|---|
| Open-Meteo Historical Weather (ERA5-Land) | Open-Meteo | Global | ~10 km | 1940 -- present |
The annual precipitation for each year is computed as the annual sum of daily precipitation values (total mm per calendar year), then converted to centimetres by dividing by 10. This differs from the temperature KPI, which uses annual means.
The 1961--1990 WMO baseline is computed as the arithmetic mean of annual precipitation sums within that 30-year window. Sites with sparse historical records before 1961 may have a slightly shorter effective baseline window.
The quality grade (A--E) is determined by mapping the absolute precipitation value (cm) to fixed range brackets -- not the percentage delta. This means the grade reflects the site's absolute rainfall level rather than just its trend.
For the multi-window comparisons, each triennium is the 3-year window centred on the target year (e.g., "vs. 10 years ago" compares the current 3-year mean to the mean of the 3 years centred 10 years before the most recent year).
Future scenario projections (SSP1-2.6, SSP2-4.5, SSP5-8.5) come from downscaled climate model ensembles. The uncertainty range shown in the tooltip reflects inter-model spread.
WMO (2017). WMO Guidelines on the Calculation of Climate Normals. WMO-No. 1203. World Meteorological Organization, Geneva. Available at: https://library.wmo.int/doc_num.php?explnum_id=4166
Munoz Sabater, J., Dutra, E., Agusti-Panareda, A., Albergel, C., Arduini, G., Balsamo, G., Boussetta, S., Choulga, M., Harrigan, S., Hersbach, H., Martens, B., Miralles, D. G., Piles, M., Rodriguez-Fernandez, N. J., Zsoter, E., Buontempo, C., and Thepaut, J.-N. (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