{
  "schema_version": 1,
  "event": {
    "id": "landslide:np-gorkha-budhi-gandaki-2026-10-11",
    "slug": "budhi-gandaki-gorkha-landslide-2026-10",
    "type": "landslide",
    "type_label": "Landslide",
    "source_id": "np-gorkha-budhi-gandaki-2026-10-11",
    "title": "Budhi Gandaki disaster: satellites map candidate landslide areas in Gorkha",
    "description": "Budhi Gandaki valley, Gorkha District, Nepal",
    "status": "satellite analysis",
    "severity": "Satellite analysis",
    "event_date": "2026-10-11",
    "country": "Nepal",
    "province": "Gandaki Province",
    "district": "Gorkha",
    "municipalities": [
      "Chumnubri Rural Municipality",
      "Dharche Rural Municipality"
    ],
    "event_summary": "In the early hours of 11 October 2026, a mass of rock, ice and debris came down the Ungdilung Khola above Chumchet in Chumnubri Rural Municipality, Gorkha. It blocked the Syar Khola and sent a series of mud-laden surges down the Syar and Budhi Gandaki rivers. Nepal's Department of Mines and Geology timed the landslide at about 04:20 local time. It estimated the largest surge at 20–25 m high when it hit the Budhi Gandaki hydropower camp at Salleri at about 06:30. At Arughat, the river gauge passed its 5 m danger level at 07:50 and peaked at 8.43 m at 08:40. The exact mechanism is still being discussed. Early reports described a landslide dam on the Syar Khola that burst. The Department of Mines and Geology describes a high-altitude avalanche and landslide whose debris briefly ponded the Syar Khola. Landslide researcher Dave Petley reads post-event Sentinel-2 imagery as a rock-slope failure that turned into a rock avalanche and debris flow, without a dam collapse. Rain was not the trigger.",
    "reported_impacts": [
      {
        "label": "People missing",
        "value": "5 (herders at a shed on the Ungdilung Khola, Chumnubri-6); no deaths confirmed",
        "status": "official, as reported on 12–13 October; Nepal Red Cross listed 6 out of contact on 29 October",
        "source": "Kathmandu Post, citing Gorkha District Administration Office and police; NDRRMA situation report via Nepal News",
        "url": "https://kathmandupost.com/national/2026/10/12/torrent-of-black-mud-and-rocks-engulfs-settlements-along-budhigandaki",
        "date": "12–13 October 2026"
      },
      {
        "label": "People rescued by helicopter",
        "value": "95 on the first day; 1,044 between 11 and 15 October, including 70 foreign nationals",
        "status": "official",
        "source": "NDRRMA situation report via Nepal News (12 October); Gorkha Assistant Chief District Officer via Nepal News (15 October)",
        "url": "https://english.nepalnews.com/s/nation/budhigandaki-floods-more-than-1000-people-rescued-by-helicopter/",
        "date": "12 and 15 October 2026"
      },
      {
        "label": "Houses damaged or destroyed",
        "value": "about 204 across Chumnubri, Dharche, Arughat (Gorkha) and Tripurasundari (Dhading)",
        "status": "provisional; the split between destroyed and damaged was not confirmed",
        "source": "NDRRMA situation report via Nepal News",
        "url": "https://english.nepalnews.com/s/nation/budhi-gandaki-flash-flood-authorities-estimate-relief-needs-for-21-days/",
        "date": "12 October 2026"
      },
      {
        "label": "Households affected",
        "value": "more than 550",
        "status": "provisional; Nepal Red Cross counted 146 on 29 October, probably with a different scope",
        "source": "WFP, citing NDRRMA",
        "url": "https://reliefweb.int/disaster/ff-2026-000189-npl",
        "date": "13 October 2026"
      },
      {
        "label": "Bridges",
        "value": "2 motorable and 2 suspension bridges lost, including the Arughat bridge linking Gorkha and Dhading",
        "status": "provisional; later Nepal Red Cross figures are higher (2 permanent, 1 Bailey and 6 suspension)",
        "source": "WFP, citing NDRRMA; Nepal Red Cross Bulletin 04",
        "url": "https://website-api.nrcs.org/media/news/attachments/Gorkha_Flash_Flood__Bulletin_4.pdf",
        "date": "13 and 29 October 2026"
      },
      {
        "label": "Hydropower",
        "value": "3 projects under construction damaged; the 341 MW Budhi Gandaki project camp at Salleri was swept away",
        "status": "official",
        "source": "NDRRMA situation report via Nepal News; Department of Mines and Geology report via Telangana Today/IANS",
        "url": "https://english.nepalnews.com/s/nation/budhi-gandaki-flash-flood-authorities-estimate-relief-needs-for-21-days/",
        "date": "12?14 October 2026"
      }
    ],
    "source_updated_at": "2026-11-13",
    "checked_at": "2026-11-13T12:57:33Z",
    "imagery_before": "1–6 October 2026",
    "imagery_after": "21–26 October 2026",
    "candidate_count": 205,
    "candidate_area_ha": 810.3,
    "candidate_count_by_confidence": {
      "higher": 1,
      "moderate": 187,
      "lower": 17
    },
    "candidate_area_ha_by_confidence": {
      "higher": 0.3,
      "moderate": 785.6,
      "lower": 24.4
    },
    "valley_change_count": 78,
    "valley_change_area_ha": 52.7,
    "road_length_near_candidates_m": 27695.0,
    "buildings_within_50m": 126,
    "optical_comparison_coverage_pct": 82.7,
    "sar_coverage_pct": 100.0,
    "area_km2": 8.103,
    "bbox": [
      84.8,
      28.1,
      85.08,
      28.55
    ],
    "geometry": {
      "type": "Polygon",
      "coordinates": [
        [
          [
            84.8,
            28.1
          ],
          [
            85.08,
            28.1
          ],
          [
            85.08,
            28.55
          ],
          [
            84.8,
            28.55
          ],
          [
            84.8,
            28.1
          ]
        ]
      ]
    },
    "headline_figure": "205 candidate areas covering 8.10 km²",
    "source_url": "https://reliefweb.int/map/nepal/satellite-detected-mudflow-11-october-2026-gorkha-district-gandaki-province-nepal-imagery-analysis-11102026-published-15102026-v1",
    "source_name": "TechnicalGIS analysis of Copernicus Sentinel-2 and Sentinel-1 data",
    "licence": "Derived map and data: CC BY 4.0 (TechnicalGIS); OSM-derived attributes: ODbL 1.0",
    "licence_url": "https://creativecommons.org/licenses/by/4.0/",
    "attribution": "Contains modified Copernicus Sentinel data [2026]. © OpenStreetMap contributors, available under the Open Database Licence (ODbL).",
    "area_method": "Candidate area is the planimetric area of the 10 m UTM 45N pixels in each polygon; it is not corrected for slope.",
    "analysis_note": "Satellite-detected candidate landslide areas are surfaces where vegetation was lost or radar backscatter changed between the before and after images. They are not confirmed landslides and have not been checked on the ground.",
    "map_renderer": "landslide-2"
  },
  "coverage": {
    "initial_area": "Budhi Gandaki valley, Gorkha District, Nepal",
    "provider": "Copernicus Sentinel-1 and Sentinel-2 (via Microsoft Planetary Computer)",
    "scope_note": "The analysis covers a 0.28° × 0.45° box around the Budhi Gandaki valley, Gorkha District, Nepal. Changes outside it, and slides smaller than the minimum mapped size, are not included."
  },
  "captured_at": "2026-11-13T12:57:33Z",
  "method": {
    "summary": "Cloud-masked Sentinel-2 composites before and after the event were compared for vegetation loss (NDVI), after removing the typical seasonal fall for each altitude band; above the alpine limit, optical change also needed radar support. Speckle-filtered Sentinel-1 VH backscatter from two orbit directions was compared to corroborate the optical change and to fill gaps where cloud or shadow hid the ground.",
    "thresholds": {
      "dndvi_min": 0.2,
      "season_band_m": 200.0,
      "alpine_radar_required_m": 4000.0,
      "post_ndvi_max": 0.25,
      "dark_nir_max": 0.035,
      "snow_ndsi_min": 0.4,
      "water_ndwi_min": 0.2,
      "slope_min_deg": 15.0,
      "sar_db_min": 3.0,
      "sar_only_db_min": 4.0,
      "sar_window_px": 5,
      "min_area_ha": 0.2,
      "sar_only_min_area_ha": 0.5,
      "river_buffer_m": 300.0,
      "road_buffer_m": 30.0,
      "building_buffer_m": 50.0,
      "place_distance_m": 1000.0
    },
    "masks": [
      "slopes gentler than 15° (Copernicus DEM GLO-30)",
      "water (Sentinel-2 scene classification and NDWI)",
      "cloud and cloud shadow (Sentinel-2 scene classification)",
      "terrain shadow (very dark near-infrared)",
      "snow and ice (scene classification and NDSI)",
      "cropland, built-up land, water and wetland (ESA WorldCover 2021)",
      "OpenStreetMap buildings and residential land"
    ],
    "confidence": {
      "higher": "optical and radar change agree",
      "moderate": "optical change only",
      "lower": "radar change only, where cloud or shadow hid the optical view"
    },
    "not_measured": [
      "confirmed landslides",
      "casualties",
      "damage to individual buildings",
      "landslide volume or depth",
      "slides smaller than 0.2 ha"
    ]
  },
  "analysis": {
    "grid": {
      "crs": "EPSG:32645",
      "pixel_m": 10.0,
      "width": 2831,
      "height": 5035,
      "bounds": [
        283860.0,
        3109760.0,
        312170.0,
        3160110.0
      ]
    },
    "candidate_count": 205,
    "candidate_area_ha": 810.3,
    "candidate_area_ha_by_confidence": {
      "higher": 0.3,
      "moderate": 785.6,
      "lower": 24.4
    },
    "candidate_count_by_confidence": {
      "higher": 1,
      "moderate": 187,
      "lower": 17
    },
    "valley_change_count": 78,
    "valley_change_area_ha": 52.7,
    "optical_comparison_coverage_pct": 82.7,
    "sar_coverage_pct": 100.0,
    "road_length_near_candidates_m": 27695.0,
    "buildings_within_50m": 126,
    "osm_retrieved": "2026-11-13T11:51:28Z"
  },
  "imagery": {
    "sentinel2": {
      "before": [
        "S2C_MSIL2A_20261001T045701_R119_T45RUM_20261001T095204",
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        "S2A_MSIL2A_20261003T050231_R119_T45RUM_20261003T100809",
        "S2A_MSIL2A_20261003T050231_R119_T45RTM_20261003T100809",
        "S2B_MSIL2A_20261006T045659_R119_T45RUM_20261006T085035",
        "S2B_MSIL2A_20261006T045659_R119_T45RTM_20261006T085035"
      ],
      "after": [
        "S2C_MSIL2A_20261021T045831_R119_T45RUM_20261021T094504",
        "S2C_MSIL2A_20261021T045831_R119_T45RTM_20261021T094504",
        "S2A_MSIL2A_20261023T050231_R119_T45RUM_20261023T100606",
        "S2A_MSIL2A_20261023T050231_R119_T45RTM_20261023T100606",
        "S2B_MSIL2A_20261026T045909_R119_T45RUM_20261026T103133",
        "S2B_MSIL2A_20261026T045909_R119_T45RTM_20261026T103133"
      ],
      "before_label": "1–6 October 2026",
      "after_label": "21–26 October 2026"
    },
    "sentinel1_rtc": {
      "descending-19": {
        "before": [
          "S1D_IW_GRDH_1SDV_20260917T001845_20260917T001910_004610_008985_rtc",
          "S1D_IW_GRDH_1SDV_20260929T001845_20260929T001910_004785_008F91_rtc"
        ],
        "after": [
          "S1D_IW_GRDH_1SDV_20261023T001845_20261023T001910_005135_009BBB_rtc",
          "S1D_IW_GRDH_1SDV_20261104T001845_20261104T001910_005310_00A1B9_rtc"
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      },
      "ascending-85": {
        "before": [
          "S1D_IW_GRDH_1SDV_20260921T122142_20260921T122207_004676_008BC6_rtc",
          "S1D_IW_GRDH_1SDV_20261003T122142_20261003T122207_004851_0091DF_rtc"
        ],
        "after": [
          "S1D_IW_GRDH_1SDV_20261015T122142_20261015T122207_005026_0097FB_rtc",
          "S1D_IW_GRDH_1SDV_20261108T122142_20261108T122207_005376_00A3FE_rtc"
        ]
      }
    },
    "dem": [
      "Copernicus_DSM_COG_10_N28_00_E084_00_DEM",
      "Copernicus_DSM_COG_10_N28_00_E085_00_DEM"
    ],
    "worldcover": "ESA_WorldCover_10m_2021_v200_N27E084"
  },
  "sources": [
    {
      "name": "Copernicus Sentinel-2 Level-2A surface reflectance",
      "url": "https://planetarycomputer.microsoft.com/dataset/sentinel-2-l2a",
      "licence": "Copernicus Sentinel data terms (free, full and open)",
      "licence_url": "https://sentinels.copernicus.eu/documents/247904/690755/Sentinel_Data_Legal_Notice",
      "attribution": "Contains modified Copernicus Sentinel data [2026]"
    },
    {
      "name": "Copernicus Sentinel-1 radiometrically terrain-corrected backscatter (from GRD)",
      "url": "https://planetarycomputer.microsoft.com/dataset/sentinel-1-rtc",
      "licence": "Copernicus Sentinel data terms (free, full and open); RTC processing by Microsoft Planetary Computer, CC BY 4.0",
      "licence_url": "https://sentinels.copernicus.eu/documents/247904/690755/Sentinel_Data_Legal_Notice",
      "attribution": "Contains modified Copernicus Sentinel data [2026]"
    },
    {
      "name": "Copernicus DEM GLO-30",
      "url": "https://planetarycomputer.microsoft.com/dataset/cop-dem-glo-30",
      "licence": "Copernicus DEM licence (free, worldwide, with attribution)",
      "licence_url": "https://spacedata.copernicus.eu/documents/20123/121286/CSCDA_ESA_Mission-specific+Annex_31_Oct_22.pdf",
      "attribution": "Copernicus DEM GLO-30 © DLR e.V. 2010–2014 and © Airbus Defence and Space GmbH 2014–2018, provided under COPERNICUS by the European Union and ESA"
    },
    {
      "name": "ESA WorldCover 10 m 2021 v200",
      "url": "https://planetarycomputer.microsoft.com/dataset/esa-worldcover",
      "licence": "CC BY 4.0",
      "licence_url": "https://creativecommons.org/licenses/by/4.0/",
      "attribution": "© ESA WorldCover project 2021 / Contains modified Copernicus Sentinel data (2021) processed by ESA WorldCover consortium"
    },
    {
      "name": "OpenStreetMap roads, paths, buildings, places and rivers (Overpass API)",
      "url": "https://www.openstreetmap.org/copyright",
      "licence": "Open Database Licence (ODbL) 1.0",
      "licence_url": "https://opendatacommons.org/licenses/odbl/1-0/",
      "attribution": "© OpenStreetMap contributors, available under the Open Database Licence (ODbL)"
    },
    {
      "name": "EOX Maps WMS (OpenStreetMap locator)",
      "url": "https://tiles.maps.eox.at/wms",
      "licence": "OpenStreetMap data under ODbL; rendering by EOX and MapServer",
      "licence_url": "https://opendatacommons.org/licenses/odbl/1-0/",
      "attribution": "Locator: data © OpenStreetMap contributors (ODbL); rendering © EOX and MapServer"
    }
  ],
  "references": [
    {
      "publisher": "UNOSAT / International Charter Space and Major Disasters (via ReliefWeb)",
      "title": "Satellite detected mudflow on 11 October 2026, Gorkha District, Gandaki Province, Nepal (v1)",
      "date": "15 October 2026",
      "url": "https://reliefweb.int/map/nepal/satellite-detected-mudflow-11-october-2026-gorkha-district-gandaki-province-nepal-imagery-analysis-11102026-published-15102026-v1"
    },
    {
      "publisher": "Sentinel Asia",
      "title": "Flood in Nepal (activation requested by DHM; escalated to the International Charter; GLIDE FF-2026-000189-NPL)",
      "date": "11 October 2026",
      "url": "https://sentinel-asia.org/EO/2026/article20261010NP.html"
    },
    {
      "publisher": "ICIMOD",
      "title": "Landslide-dam breach may have triggered Budhi Gandaki flash flood (media advisory)",
      "date": "11 October 2026",
      "url": "https://www.icimod.org/press-releases/landslide-dam-breach-may-have-triggered-budhi-gandaki-flash-flood/"
    },
    {
      "publisher": "Nepal Red Cross Society",
      "title": "Gorkha Flash Flood Situation Bulletin 04",
      "date": "29 October 2026",
      "url": "https://website-api.nrcs.org/media/news/attachments/Gorkha_Flash_Flood__Bulletin_4.pdf"
    },
    {
      "publisher": "Telangana Today / IANS, summarising the Department of Mines and Geology report released by NDRRMA",
      "title": "Landslide triggering Budhi Gandaki River floods in Nepal unleashed energy equivalent to 3.5-magnitude quake: Report",
      "date": "14 October 2026",
      "url": "https://telanganatoday.com/landslide-triggering-budhi-gandaki-river-floods-in-nepal-unleashed-energy-equivalent-to-3-5-magnitude-quake-report"
    },
    {
      "publisher": "Dave Petley, The Landslide Blog (Eos/AGU)",
      "title": "The 11 October 2026 landslide and debris flow/flood on the Budhi Gandaki River in Gorkha district, Nepal",
      "date": "12 October 2026",
      "url": "https://eos.org/thelandslideblog/the-11-october-2026-landslide-and-debris-flow-flood-on-the-budhi-gandaki-river-in-gorkha-district-nepal"
    },
    {
      "publisher": "Dave Petley, The Landslide Blog (Eos/AGU)",
      "title": "Sentinel images of the source of the 11 October 2026 landslide and debris flow along the Budhi Gandaki River in Nepal",
      "date": "5 November 2026",
      "url": "https://eos.org/thelandslideblog/budhi-gandaki-2"
    },
    {
      "publisher": "EU Agency for the Space Programme",
      "title": "Landslide-triggered flash flood sweeps through Nepal's Himalayan valleys (Copernicus image of the day)",
      "date": "14 October 2026",
      "url": "https://eu-space.europa.eu/components/earth-observation-copernicus/image-of-the-day/landslide-triggered-flash-flood-sweeps-through-nepals-himalayan-valleys"
    },
    {
      "publisher": "BBC News (Navin Singh Khadka)",
      "title": "Homes and bridges swept away as fresh floods hit Nepal",
      "date": "12 October 2026",
      "url": "https://www.bbc.com/news/articles/ck86zppejjw3o"
    },
    {
      "publisher": "The Kathmandu Post (Hariram Upreti)",
      "title": "Torrent of black mud and rocks engulfs settlements along Budhigandaki",
      "date": "12 October 2026",
      "url": "https://kathmandupost.com/national/2026/10/12/torrent-of-black-mud-and-rocks-engulfs-settlements-along-budhigandaki"
    },
    {
      "publisher": "Nepal News",
      "title": "Budhi Gandaki flash flood: authorities estimate relief needs for 21 days (NDRRMA situation report)",
      "date": "12 October 2026",
      "url": "https://english.nepalnews.com/s/nation/budhi-gandaki-flash-flood-authorities-estimate-relief-needs-for-21-days/"
    },
    {
      "publisher": "Nepal News",
      "title": "Budhigandaki floods: more than 1,000 people rescued by helicopter",
      "date": "15 October 2026",
      "url": "https://english.nepalnews.com/s/nation/budhigandaki-floods-more-than-1000-people-rescued-by-helicopter/"
    }
  ],
  "cross_check": "No Copernicus Emergency Management Service activation was found for this event, and ICIMOD has not published a landslide delineation. The nearest independent product is UNOSAT's preliminary map for the International Charter, made from Sentinel-2 imagery of 11 October. It estimates about 18 km² affected by flood water or mudflow across a 470 km² analysis area and about 33 km of road affected; UNOSAT notes it has not been validated in the field. That map measures the flood and mudflow footprint, whereas ours looks for vegetation loss on slopes, so the two complement rather than duplicate each other. Our valley-floor change class is the closer comparison with UNOSAT's footprint. The main landslide source reported by Dave Petley lies at about 28.534°N, 84.935°E, above 5,000 m on the west side of the valley, south of Chamar. Much of that zone is bare rock, snow or ice, so a vegetation-loss method is not expected to pick it up. Sentinel-1 radar there shows no strong, consistent change: within 1 km of the reported source the median VH change is under 1 dB, and about a tenth of pixels rose by 3 dB or more, which fresh snow or ice alone could cause. The radar therefore neither confirms nor rules out the source. The August 2026 Rasuwa–Langtang disaster (Copernicus EMS activation EMSR927) happened in a different valley and was not used to validate this analysis.",
  "revision": 2,
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