TidewatchOpen the map

Methodology

How Tidewatch works, and where it shouldn’t be trusted

Tidewatch is a navigator over authoritative datasets. This page explains exactly what each number in a place brief is, where it comes from, and the caveats to keep in mind before you put it in a report.

The problem we’re solving

Our research (docs/PROBLEM_RESEARCH.md) kept finding the same pain point. The data exists, but it is fragmented: spread across many portals and formats, with unclear reuse terms. Interviews for a USGS study of coastal practitioners included the line “There are too many tools… We don’t need another tool” and a request for “a map where the user can define an area and their relevant site-specific reports or data would come up” (USGS SIR 2023-5081). Ecologists on Reddit describe “many disjointed mapping and data management elements” (r/ecology). For marine protection, coverage statistics can overstate how much ocean is actually protected (Grorud-Colvert et al.).

So Tidewatch does not add another dataset. It answers “what is happening here, and can I cite it?” with one click, and shows the licence of every layer it touches.

How a place brief is built

When you click the map, the Go API (GET /api/identify) runs these steps in parallel:

  1. Jurisdiction and ecosystem: point-in-polygon tests (even–odd rule, holes respected) against simplified Marine Regions EEZ v12, NOAA LME66, Natural Earth marine areas and Natural Earth 1:50m countries, all held in memory. With PostGIS enabled, ?precise=1 queries the full-resolution geometry instead.
  2. Protected areas: a live point query to UNEP-WCMC’s WDPA MapServer (layer 1, polygons). The results are shown but never stored or exported.
  3. Tide gauges: the three nearest UHSLC fast-delivery stations by great-circle (haversine) distance.
  4. Heat stress: the last 90 days of NOAA Coral Reef Watch values at the nearest 0.05° grid cell, via ERDDAP, skipped on land.

Upstream responses are cached server-side (6 h by default). Clicks are snapped to the 0.05° CRW grid, so nearby clicks share the same cache entry.

Coral heat stress

Values come from NOAA CRW’s daily global 5 km product, version 3.1 (dhw_5km on PacIOOS ERDDAP, with a fallback to NOAA CoastWatch). SST is CRW’s blended night-time sea surface temperature. The anomaly is relative to CRW’s daily climatology. Degree Heating Weeks (DHW) are HotSpots of at least 1 °C accumulated over 12 weeks. The Bleaching Alert Area follows the v3.1 scale: No Stress, Watch, Warning and Alert Levels 1–5. Alert Levels 3–5 (DHW ≥ 12, 16, 20) were added in December 2023 to describe heat stress beyond anything seen before (CRW methodology).

Long ranges are thinned so a chart has at most about 400 samples. The stride is shown under the chart, and the CSV export has the same samples. For daily values over long periods, use the linked ERDDAP query.

Satellite heat stress predicts the risk of bleaching. It does not observe bleaching. Reef-scale and at-depth temperatures can differ from 5 km satellite SST.

Sea level

Daily values come from the UHSLC fast-delivery dataset (global_daily_fast on the UHSLC ERDDAP). Tidewatch averages them into monthly means and keeps only months with at least 15 daily values. A linear trend (ordinary least squares on the monthly means) is reported only when the record spans at least 10 years. Shorter records are dominated by interannual variability such as ENSO.

This is relative sea level at the gauge. It includes vertical land motion such as subsidence or uplift, so it is not directly comparable with satellite-altimetry global mean sea level. Fast-delivery data get only basic quality control. Use UHSLC research-quality data or PSMSL for publication.

Tree cover loss

The tree-cover loss layer shows the Hansen/UMD Global Forest Change data (v1.13, 2001–2025, canopy density ≥ 30%) using Global Forest Watch’s public tiles. Those tiles encode loss intensity in the red channel and year of loss in the blue channel. Tidewatch decodes them in the browser with a WebGL shader, colours each pixel by year (viridis) and filters by the year range you choose. Clicking reads the displayed pixel. Below zoom 12 one screen pixel summarises many 30 m Landsat pixels.

Tree cover loss is not the same as deforestation. It includes fire, harvest, storms and plantation rotation, and some of it regrows. Accuracy assessments show that small or selective clearing can be missed, so validate locally before any compliance use (for example under the EUDR).

Protected areas

Protected-area polygons and attributes come live from the World Database on Protected and Conserved Areas (UNEP-WCMC & IUCN). The brief shows the designation, IUCN category, status year and the NO_TAKE field as reported. Reported coverage is not the same as effective protection. The Protected Planet Report 2024 found that about 8.4% of the ocean was in MPAs, but only about 2.8% was fully or highly protected (Protected Planet Report 2024).

Licences & exports

Every layer has a licence summary taken from server/internal/catalog. The app enforces it:

Every layer, cited

Coral bleaching alert area

Open

NOAA Coral Reef Watch daily 5 km Bleaching Alert Area: the satellite heat-stress level that predicts coral bleaching and mortality risk.

Resolution
0.05° (~5 km)
Cadence
Daily (1985–present)
Cite
NOAA Coral Reef Watch (2018, updated daily). NOAA Coral Reef Watch Version 3.1 Daily Global 5km Satellite Coral Bleaching Heat Stress Monitoring Products. College Park, Maryland, USA: NOAA Coral Reef Watch.
  • Satellite SST measures the skin of the sea surface; reef-scale and at-depth temperatures can differ.
  • Alert levels 3–5 were added in Dec 2023 to describe unprecedented heat stress.

Degree Heating Weeks

Open

Accumulated heat stress over the past 12 weeks (°C-weeks). At 4 °C-weeks there is a risk of reef-wide bleaching. At 8 or more there is also a risk of mortality in heat-sensitive corals (CRW v3.1).

Resolution
0.05° (~5 km)
Cadence
Daily
Cite
NOAA Coral Reef Watch (2018, updated daily). Daily Global 5km Satellite Coral Bleaching Degree Heating Week Product, v3.1.

Sea surface temperature anomaly

Open

GHRSST MUR L4 daily SST anomaly relative to a 2003–2014 climatology. Marine heatwaves show up as persistent warm patches.

Resolution
0.01° (~1 km), rendered to zoom 7
Cadence
Daily, ~1 day latency
Cite
JPL MUR MEaSUREs Project. 2015. GHRSST Level 4 MUR Global Foundation Sea Surface Temperature Analysis (v4.1). PO.DAAC, CA, USA. doi:10.5067/GHGMR-4FJ04
  • Raster colours are rendered by NASA GIBS; click the map for the exact NOAA CRW value at a point.

Sea surface temperature

Open

GHRSST MUR L4 daily foundation sea surface temperature.

Resolution
0.01° (~1 km), rendered to zoom 7
Cadence
Daily
Cite
JPL MUR MEaSUREs Project. 2015. GHRSST Level 4 MUR Global Foundation Sea Surface Temperature Analysis (v4.1). PO.DAAC, CA, USA. doi:10.5067/GHGMR-4FJ04

Chlorophyll-a (PACE OCI)

Open

Daily chlorophyll-a concentration from NASA's PACE Ocean Color Instrument — a proxy for phytoplankton biomass, blooms and nutrient pollution.

Resolution
~1 km, rendered to zoom 7
Cadence
Daily (2024–present); gaps under cloud and sun-glint
Cite
NASA Ocean Biology Processing Group. PACE OCI Level-2 Chlorophyll-a. NASA OB.DAAC, Greenbelt, MD, USA.
  • Daily swaths have cloud gaps; scrub the time slider to fill in coverage.

Protected areas (WDPA)

View onlyNon-commercial

World Database on Protected and Conserved Areas — the official dataset used to track progress toward the 30×30 target (Kunming-Montreal GBF Target 3).

Resolution
Vector polygons (national reporting)
Cadence
Monthly
Licence
WDPCA Terms (non-commercial; no redistribution) · Displayed and queried live from UNEP-WCMC. Tidewatch never re-serves or exports WDPA geometry or attributes. Commercial users must access WDPA via IBAT.
Cite
UNEP-WCMC and IUCN (2026), Protected Planet: The World Database on Protected and Conserved Areas (WDPCA) [On-line], [October 2026], Cambridge, UK: UNEP-WCMC and IUCN. Available at: www.protectedplanet.net.
  • Coverage ≠ protection quality: WDPA records the legal designation, not whether an MPA is implemented or what activities are allowed.
  • ‘No take’ is often ‘Not Reported’ or ‘None’ even for zoned parks (e.g. the Great Barrier Reef Marine Park polygon), because zone data is not in WDPA.

MPA coverage vs 30×30, by country

View onlyNon-commercial

Share of each country's marine area inside protected areas or OECMs (latest year reported, up to 2025), against the 30% target for 2030. Click a country or EEZ for the trend.

Resolution
Country
Cadence
Annual (snapshot in data/processed/stats)
Licence
World Bank data CC BY 4.0; derived from WDPA/WD-OECM (non-commercial) · The coverage figures are published by the World Bank, but they are computed from WDPA, whose terms forbid commercial use. Tidewatch shows them view-only and does not export them.
Cite
World Bank, World Development Indicators: Marine protected areas (% of territorial waters) [ER.MRN.PTMR.ZS]. Source data: UNEP-WCMC and IUCN, Protected Planet (WDPA and WD-OECM). Retrieved via api.worldbank.org.
  • National figures: a country's overseas EEZs may be included in its total or reported separately; the EEZ you click may not match the figure exactly.
  • Designation ≠ protection: many MPAs allow fishing or lack management (see Protected Planet reports).

Exclusive Economic Zones

Attribution

200 nautical-mile maritime zones (Marine Regions World EEZ v12, low-res). Tells you whose jurisdiction — and whose reporting — a patch of ocean falls under.

Resolution
Generalised (low-res) and further simplified for the web
Cadence
Versioned (v12, 2023)
Licence
CC BY 4.0 · Marine Regions asks that full datasets are downloaded from marineregions.org; Tidewatch exports single, simplified features only. Not for legal or navigational use.
Cite
Flanders Marine Institute (2023). Maritime Boundaries Geodatabase: Maritime Boundaries and Exclusive Economic Zones (200NM), version 12. Available online at https://www.marineregions.org/. doi:10.14284/632
  • Boundaries are simplified (~6% of vertices kept) for display; do not use for legal or area calculations.

Large Marine Ecosystems

Attribution

66 Large Marine Ecosystems — coastal regions defined by bathymetry, hydrography, productivity and food webs; the unit used by many fisheries and GEF assessments.

Resolution
Simplified vector
Cadence
Static
Licence
CC BY 4.0
Cite
Sherman, K. et al. Large Marine Ecosystems of the World (LME66). Distributed by MarineRegions.org (Flanders Marine Institute).

Continental shelf & deep ocean

Open

Natural Earth bathymetry polygons at the 200 m (shelf break) and 2,000 m contours.

Resolution
1:10m, simplified
Cadence
Static
Cite
Natural Earth. Free vector and raster map data @ naturalearthdata.com.

GEBCO bathymetry (shaded)

Attribution

GEBCO global terrain model of the seafloor, shaded relief.

Resolution
15 arc-second grid
Cadence
Annual releases
Cite
GEBCO Compilation Group. GEBCO Grid (latest release served by wms.gebco.net). Cite the specific grid release and DOI listed at gebco.net when publishing.

Tide gauges (UHSLC)

Attribution

University of Hawaiʻi Sea Level Center fast-delivery tide gauges. Click one to chart its monthly mean sea level.

Resolution
326 stations
Cadence
Daily values, ~1–2 month latency
Cite
Caldwell, P. C., M. A. Merrifield, P. R. Thompson (2015), Sea level measured by tide gauges from global oceans — the Joint Archive for Sea Level holdings (NCEI Accession 0019568), NOAA NCEI. doi:10.7289/V5V40S7W
  • Fast-delivery data are quality-controlled at a basic level only; use research-quality (RQ) data for publication-grade trends.
  • Tide gauges measure relative sea level, which includes local land subsidence or uplift.

Apparent fishing effort

AttributionNon-commercial

Global Fishing Watch AIS-based apparent fishing effort. Requires a free GFW API token — stubbed in v1.

Resolution
0.01°
Cadence
Daily, ~72 h latency
Licence
CC BY-NC 4.0 (API terms apply) · Set GFW_API_TOKEN to enable (roadmap).
Cite
Global Fishing Watch. www.globalfishingwatch.org

Tree cover loss (Hansen / UMD)

Attribution

Annual 30 m tree cover loss 2001–2025 from the University of Maryland GLAD lab, at ≥30% canopy density. Coloured by year of loss.

Resolution
30 m (Landsat)
Cadence
Annual
Licence
CC BY 4.0
Cite
Hansen, M. C. et al. 2013. High-Resolution Global Maps of 21st-Century Forest Cover Change. Science 342: 850–53. Data available from glad.earthengine.app/view/global-forest-change. doi:10.1126/science.1244693
  • Tree cover loss ≠ deforestation: it includes fire, harvest and plantation rotation, and some loss later regrows.
  • Small, scattered or selective clearing can be missed at 30 m; validate locally before compliance use (e.g. EUDR).

Active fires (VIIRS 375 m)

Open

NASA FIRMS VIIRS (NOAA-20) thermal anomalies and active fire detections for the selected day.

Resolution
375 m
Cadence
Daily, near real time
Cite
NASA FIRMS. NRT VIIRS 375 m Active Fire product VJ114IMGTDL_NRT. Available on-line https://earthdata.nasa.gov/firms. doi:10.5067/FIRMS/VIIRS/VJ114IMGT_NRT.002

Mangrove extent 2020 (GMW v3)

Attribution

Global Mangrove Watch v3 mangrove extent for 2020, queried live from UNEP-WCMC. Visible from zoom 9.

Resolution
~25 m
Cadence
Annual extents (v3: 1996–2020)
Licence
CC BY 4.0
Cite
Bunting, P. et al. (2022). Global Mangrove Extent Change 1996–2020: Global Mangrove Watch Version 3.0. Remote Sensing 14(15), 3657. doi:10.3390/rs14153657

Tree cover loss by country (2001–2024)

Attribution

Total tree cover loss per country, 2001–2024, from the UMD GLAD / Global Forest Watch annual statistics. Click a country for the year-by-year chart.

Resolution
Country
Cadence
Annual (snapshot in data/processed/stats)
Licence
CC BY 4.0
Cite
Hansen, M. C. et al. (2013). High-Resolution Global Maps of 21st-Century Forest Cover Change. Science 342, 850–853 (updated annually by UMD GLAD). Country totals: Global Forest Watch (2025), processed by Our World in Data. doi:10.1126/science.1244693
  • Tree cover loss is not deforestation: it includes plantation harvest, fire and natural disturbance, and regrowth is not netted out.
  • GFW notes that methodology changes around 2011–2015 make later years not strictly comparable with earlier ones.

Mangrove change by country (1996–2020)

Attribution

Net change in mangrove extent per country between 1996 and 2020, from the Global Mangrove Watch v3.0 country statistics. Click a country for the extent series with 95% confidence bounds.

Resolution
Country
Cadence
GMW epochs 1996, 2007–2010, 2015–2020
Licence
CC BY 4.0
Cite
Bunting, P. et al. (2022). Global Mangrove Extent Change 1996–2020: Global Mangrove Watch Version 3.0. Remote Sensing 14(15), 3657. Data: Zenodo, doi:10.5281/zenodo.6894273. doi:10.5281/zenodo.6894273
  • Country totals have wide 95% confidence intervals, and the authors rate gain and loss classes (~58–61% accuracy) below extent (~87%).

Mangrove extent 1996 (GMW v3, outline)

Attribution

Global Mangrove Watch v3 extent for 1996, drawn as an outline. Turn on with the 2020 extent: outlines with no green fill inside are mangroves lost since 1996, and green outside the outlines is gain. Visible from zoom 9.

Resolution
~25 m
Cadence
1996 epoch
Licence
CC BY 4.0
Cite
Bunting, P. et al. (2022). Global Mangrove Extent Change 1996–2020: Global Mangrove Watch Version 3.0. Remote Sensing 14(15), 3657. doi:10.3390/rs14153657
  • Polygons are generalised for display. The authors caution that pixel-level gain and loss is less accurate than extent, so treat small differences as uncertain.

Countries

Open

Natural Earth admin-0 countries (1:50m).

Resolution
1:50m, simplified
Cadence
Versioned
Cite
Natural Earth. Free vector and raster map data @ naturalearthdata.com.
  • Natural Earth shows de facto boundaries; Tidewatch takes no position on disputed borders.

Seas & ocean names

Open

Natural Earth marine areas (oceans, seas, gulfs, bays).

Resolution
1:10m, simplified
Cadence
Versioned
Cite
Natural Earth. Free vector and raster map data @ naturalearthdata.com.

News (geotagged stories)

View onlyNon-commercial

Environment stories from Tidewatch's news feeds, placed by the countries, seas, EEZs, cities and features they mention. Pins are clustered, coloured by the most common topic and sized by the number of stories. Click one to read the stories.

Resolution
Place centroids (country label points, sea and EEZ centroids, cities)
Cadence
Every 4 hours
Licence
Headlines and links only; each story stays under its publisher's terms · Gazetteer: Natural Earth (public domain), mledoze/countries (ODbL 1.0), Marine Regions (CC BY 4.0), Wikidata (CC0).
Cite
Tidewatch news layer: headlines from the publishers listed on /news, geotagged with Natural Earth, Marine Regions and Wikidata place names.
  • Places are matched automatically from headlines and summaries (English translations when available). Expect some mis-tags, such as a publisher's home country or a place mentioned only in passing.
  • A story about several places counts at each of them.
  • Needs the Cloudflare news Worker (PUBLIC_NEWS_API). The Go API's news fallback has no geotags, so this layer stays empty and briefs fall back to a text search.

Basemaps: Dark ocean (Esri, tinted) (Esri, HERE, Garmin, © OpenStreetMap contributors, and the GIS user community) · Offline (Natural Earth) (Made with Natural Earth) · Ocean (Esri) (Esri, GEBCO, NOAA, National Geographic, Garmin, HERE, Geonames.org, and other contributors) · Blue Marble (NASA) (NASA Blue Marble · GIBS) · OpenStreetMap (© OpenStreetMap contributors)

Known limitations