The Monthly Warming Stripes KPI visualizes monthly temperature anomalies at a monitored site relative to the 1961--1990 WMO climatological baseline. For each of the last 5 years, a line chart is drawn with the 12 months on the horizontal axis. Each point on the line represents the temperature departure for that month: how much warmer or cooler that month was compared to its long-term average. Points and line segments are colored on a continuous gradient from deep blue (−1 °C, colder than baseline) through yellow (near 0 °C, neutral) to dark red (+3 °C, strongly warmer than baseline).
This KPI is visualization-only -- it has no A--E quality grade and no numeric composite score. Its purpose is to reveal long-term warming trends and seasonal patterns across multiple years in a single glance.
ESRS alignment: E1-1, ESRS E1-4.
The anomaly for each month is the difference between the observed monthly temperature and the corresponding long-term baseline:
where = mean near-surface air temperature (2 m) for a given year and calendar month at the site location (ERA5-Land reanalysis), = climatological mean for the same calendar month over the WMO standard reference period 1961--1990
The anomaly value is clamped to the range [−1 °C, +3 °C] and mapped to a continuous 11-stop color gradient from deep blue (cold) through yellow (neutral) to dark red (warm).
Data are sourced from Open-Meteo Historical Weather (ERA5-Land reanalysis) at approximately 10 km spatial resolution, covering the period from 1940 to the present.
Line Chart. A multi-row SVG line chart, one row per year, showing temperature anomalies for each of the 12 calendar months.
Purpose: Answers the question "For each month over the past 5 years, was this site warmer or cooler than the historical average -- and by how much?"
Description: The component is placed in the Microclimate section of the Assessment page, spanning the full column width. A header row shows abbreviated month labels (Jan through Dec). Below, each year occupies one row: a year badge on the left (e.g., "2022") and an SVG chart on the right. Each SVG chart contains:
Below all year rows, a continuous color legend bar is shown, ranging from −1 °C (deep blue) on the left to +3 °C (dark red) on the right.
Temperature Anomaly
-1 °C+3 °CCold (Below baseline)Warm (Above baseline)
How it's calculated: For each month point, the displayed delta is the monthly mean temperature minus the 1961--1990 baseline mean for that calendar month. The vertical position of each point scales linearly between the global minimum and maximum delta observed across all 5 years (with the range always including 0). The color of each point and segment uses an 11-stop gradient clamped to [−1 °C, +3 °C].
Legend:
The continuous gradient legend below the chart represents:
| Approximate °C | Color | Meaning |
|---|---|---|
| −1 °C | ■ #1e40af | Deep blue -- strongly below baseline |
| −0.2 °C | ■ #3b82f6 | Light blue -- slightly below baseline |
| 0 °C | ■ #93c5fd | Very light blue -- at baseline |
| +0.2 °C | ■ #fde047 | Yellow -- slightly above baseline |
| +1.0 °C | ■ #fb923c | Orange -- moderately above baseline |
| +2.0 °C | ■ #ef4444 | Red -- significantly above baseline |
| +3.0 °C | ■ #7f1d1d | Dark red -- strongly above baseline |
Text labels below the bar: "Cold (Below baseline)" -- "Neutral (~0 °C delta)" -- "Warm (Above baseline)".
Interpretation example:
If the chart for 2024 shows all summer months (June--August) with points well above the baseline -- colored orange to red -- while winter months sit near zero (light blue/yellow), it means the site experienced anomalous summer heat in 2024 while winter temperatures remained close to historical norms. If the same pattern repeats across 2022, 2023, and 2024, it indicates a sustained multi-year summer warming trend at this site.
| Source | Provider | Coverage | Resolution | Period |
|---|---|---|---|---|
| Open-Meteo Historical Weather (ERA5-Land) | Open-Meteo | Global | ~10 km | 1940-01-01 -- present |
The anomaly computation is performed entirely in the frontend from two API endpoints. For each of the last 5 complete years, the monthly mean near-surface air temperature (ERA5-Land, 2 m height) is fetched for each calendar month at the site location. Years are fetched sequentially with a 300 ms delay between calls to avoid rate limiting. If a year fails to fetch, it is silently skipped and the chart shows fewer rows.
The baseline mean temperature for each calendar month is computed over the WMO standard reference period 1961--1990. The anomaly for each month is then calculated as the difference between the observed monthly mean and the corresponding baseline mean.
The resulting anomaly value is clamped to the range [−1 °C, +3 °C] and normalized to [0, 1] for color interpolation across 11 gradient stops (deep blue, light blue, very light blue, yellow, orange, red, dark red). Anomalies outside this range are displayed with the extreme colors without further differentiation.
The 5-year window is interactive: clicking an annual stripe in the related Annual Warming Stripes chart recenters the monthly chart to the clicked year +/- 2 years.