{"id":"44557520-6234-4a77-9263-cabfc00f4d72","first_published_at":"2025-10-02T08:30:00.000Z","published_revision":{"id":"e8b90f36-114e-46bd-a95e-a7a6c3ad08b8","revision_index":2,"previous_revision_id":"b0642be6-f3f8-47ca-88f8-84e49d9bea58","created_at":"2026-06-23T08:39:29.014Z","updated_at":"2026-06-23T13:05:35.862Z","approved_at":"2026-06-23T13:05:35.858Z","publish_at":"2026-06-26T08:30:00.000Z","metadata":[{"language":"cy-GB","title":"Eiddo sydd mewn perygl o lifogydd yng Nghymru","summary":"Mae Asesiad Bygythiad Llifogydd Cymru (FRAW) ynghyd â'r Gronfa Ddata Derbynnydd Genedlaethol 2025 (NRD 2025) yn cael eu defnyddio i benderfynu ar nifer yr eiddo (preswyl a di-breswyl) sydd mewn perygl o lifogydd o Afonydd, y Môr a Dwr Wyneb a Chyrsiau Dwr Bach yng Nghymru. Mae'r wybodaeth ar gyfer risg Heddiw a risg Newid Hinsawdd (2120) ac mae'n cynnwys presenoldeb a diffyg presenoldeb amddiffynfeydd rhag llifogydd o fewn y modelu (senarios gyda amddiffyniad a senarios heb amddiffyniad).","collection":"Nodir y posibilrwydd o lifogydd mewn tri chategori risg:\n\nRisg Uchel; Siawns sy'n fwy na neu'n hafal i 1 o bob 30 (3.3%) mewn unrhyw flwyddyn penodol.\nRisg Ganolig; Siawns sy'n llai nag 1 o bob 30 (3.3%) ond yn fwy na, neu'n hafal i 1 o bob 100 (1%) mewn unrhyw flwyddyn benodol ar gyfer afonydd a llifogydd dwr wyneb a llai nag 1 o bob 30 (3.3%) ond yn fwy na neu'n hafal i 1 o bob 200 (0.5%) ar gyfer y môr.\nRisg Isel; Siawns sy'n llai nag 1 o bob 100 (1%) ar gyfer afonydd a llifogydd dwr wyneb ac 1 o bob 200 (0.5%) ar gyfer y môr ond yn fwy na neu'n hafal i siawns 1 o bob 1,000 (0.1%) mewn unrhyw flwyddyn benodol.\n\nMae FRAW fel arfer yn cynnwys llifogydd o afonydd sydd â maint dalgylch sy'n fwy na 3 cilomedr sgwâr, a llifogydd o'r môr (ar hyd yr arfordir agored ac aberoedd llanw). Cynrychiolir cyrsiau dwr llai sydd â maint dalgylch llai na 3 cilomedr sgwâr yn y data a mapiau Dwr Wyneb FRAW.\n\nMae'r asesiad yn ystyried lleoliad a safon yr amddiffyniad a roddir gan amddiffynfeydd llifogydd ac yn addasu'r categoreiddio risg yn unol â hynny o senario 'heb amddiffyniad'.\n\nMae'r gwerthoedd cynnydd newid hinsawdd yn seiliedig ar ganllawiau Llywodraeth Cymru oedd ar gael adeg cwblhau'r prosiect FRAW gwreiddiol yn 2019. Mae'r gwerthoedd cynnydd hyn yn wahanol i'r lwfansau diwygiedig a gyhoeddwyd gan Lywodraeth Cymru ym mis Mawrth 2026. O ganlyniad, gall nifer yr eiddo amcangyfrifedig newid yn y dyfodol pan fydd y gwerthoedd cynnydd newydd yn cael eu hystyried.\n\nAr gyfer y senario heb amddiffyniad Newid Hinsawdd, rhagdybiwyd bod y safon bresennol o amddiffyn yr amddiffynfeydd rhag llifogydd yn cadw i fyny â newid hinsawdd.","quality":"Mae FRAW fel arfer yn cynnwys llifogydd o afonydd sydd â maint dalgylch sy'n fwy na 3 cilomedr sgwâr, a llifogydd o'r môr (ar hyd yr arfordir agored ac aberoedd llanw). Cynrychiolir cyrsiau dwr llai sydd â maint dalgylch llai na 3 cilomedr sgwâr yn y data a mapiau Dwr Arwyneb FRAW.\n\nMae'r asesiad yn ystyried lleoliad a safon yr amddiffyniad a roddir gan amddiffynfeydd llifogydd ac yn addasu'r categoreiddio risg yn unol â hynny o senario 'heb amddiffyniad'.\n\nEfallai y bydd mwy nag un ffynhonnell o lifogydd yn effeithio ar rai eiddo yng Nghymru, felly wrth gyfrif eiddo sydd mewn perygl, mae angen i chi fod yn ofalus nad yw'r un eiddo yn cael ei gyfrif fwy nag unwaith. Er enghraifft, os yw eiddo yn cael ei effeithio gan bob un o'r tair ffynhonnell o lifogydd, wrth adrodd yn ôl ffynonellau llifogydd, bydd yn cael ei gyfrif fel un eiddo ar gyfer afonydd, un ar gyfer y môr ac un ar gyfer dwr wyneb a chwrs dwr bach. Fodd bynnag, os ydych yn cyfrif cyfanswm yr eiddo yng Nghymru sydd mewn perygl o lifogydd, gan ddefnyddio swm y tair ffynhonnell, gellid cyfrif yr un eiddo dair gwaith.\n\nMae'r cyfrif eiddo a ddarperir yn gipolwg mewn amser yn seiliedig ar setiau data o’r un flwyddyn. Maent yn destun newid o flwyddyn i flwyddyn, wrth i ddata a methodoleg wella dros amser. Gall hyn achosi i gyfrif gynyddu neu leihau rhwng datganiadau unigol. Pan fyddwn yn cyfrif adeiladau neu eiddo, gall hyn gynnwys nifer o adeiladau yn yr un cyfeiriad.\nYn 2024 cynhyrchodd Cyfoeth Naturiol Cymru amcanestyniad ar gyfer eiddo mewn perygl ar gyfer 2120 am y tro cyntaf, ac mae hwn wedi’i ddiweddaru eleni. Mae’r amcanestyniad 2120 presennol wedi’i seilio ar ffigyrau 2025. Mae ffigyrau 2024 a 2025 yn cynnwys cyfrif eiddo sy'n cynrychioli senario wedi'i amddiffyn yn 2120 (h.y. mewn tua 100 mlynedd). Mae'r amcangyfrifon hyn yn seiliedig ar yr un rhagdybiaeth sylfaenol y bydd y safon bresennol o amddiffynfeydd rhag llifogydd yn cael eu cynnal yn y dyfodol ond maent wedi'u cyfrifo mewn dwy ffordd ychydig yn wahanol:\n \n1.\tAr gyfer cyfrif eiddo 2024, gosodwyd safon amddiffyn rhag llifogydd yn y dyfodol (2120) ar 80% o'r safon presennol. Roedd hyn yn golygu bod gostyngiad yn safon yr amddiffyn sy'n golygu bod rhai eiddo yn symud i fandiau risg uwch.\n2.\tAr gyfer cyfrif eiddo 2025, mae'r cyfrifiad wedi'i berfformio'n wahanol. Ni fu gostyngiad yn y safon amddiffyn ac mae'r lefel bresennol yn cael ei chynnal yn y dyfodol (h.y. amddiffyn rhag llifogydd sy'n darparu safon amddiffyn 100 mlynedd o heddiw yn darparu'r un safon amddiffyn 100 mlynedd yn 2120).\n \nMae gwahaniaethau rhwng cyfrif eiddo 2024 a 2025 yn dangos pa mor agored yw'r ffigurau i newid gyda dim ond ychydig o newid i'r ymagwedd sy'n sail i'r ansicrwydd wrth wneud rhagfynegiadau yn y dyfodol.\n \nDim ond un canlyniad posibl yw'r rhagdybiaeth y bydd amddiffynfeydd rhag llifogydd yn cael eu cynnal i'r un lefel o amddiffyniad. Gallai'r risg a neilltuwyd i eiddo mewn ardaloedd wedi eu hamddiffyn newid yn fawr yn y dyfodol yn dibynnu ar lefelau buddsoddi a cynnal a chadw. Cliciwch ar y ddolen am fwy o wybodaeth. Cyfoeth Naturiol Cymru / Gofynion Buddsoddi Hirdymor ar gyfer Amddiffynfeydd rhag Llifogydd yng Nghymru.","rounding_description":null,"reason":"Diweddariad i'r metadata ar ôl diwygiad i'r lwfansau, a gyhoeddwyd gan Llywodraeth Cymru ym Mawrth 2026"},{"language":"en-GB","title":"Properties at risk of flooding in Wales","summary":"The Flood Risk Assessment Wales (FRAW) modelling, together with the latest National Receptor Database 2025 (NRD 2025) are used to determine the number of properties (residential and non-residential) at risk of flooding from Rivers, the Sea and Surface Water and Small Watercourses in Wales. The information is for Present Day risk and Climate Change risk (2120) and includes both the presence and removal of flood defences within the modelling (defended and undefended scenarios).\r\n\r\n","collection":"The chance of flooding is set out in three risk categories:\r\n\r\nHigh Risk; Greater than or equal to 1 in 30 (3.3%) chance in any given year\r\nMedium Risk; Less than 1 in 30 (3.3%) but greater than or equal to 1 in 100 (1%) chance in any given year for rivers and surface water flooding and less than 1 in 30 (3.3 per cent) but greater than or equal to 1 in 200 (0.5 per cent) for the sea.\r\nLow Risk; Less than 1 in 100 (1%) for rivers and surface water flooding and 1 in 200 (0.5 per cent) for the sea but greater than or equal to 1 in 1,000 (0.1%) chance in any given year.\r\n\r\nFRAW typically includes flooding from rivers with a catchment size greater than 3 square kilometres, and flooding from the sea (both along the open coast and tidal estuaries). Smaller watercourses with a catchment size smaller than 3 square kilometres are represented in the FRAW Surface Water data and maps.\r\n\r\nThe assessment takes into account the location and standard of protection afforded by flood defences and adjusts the risk categorisation accordingly from an initial, ‘undefended’ scenario.\r\n\r\nClimate change uplift values are based on Welsh Government guidance available at the time the original FRAW project was completed in 2019. These uplift values are different to revised allowances published by Welsh Government in March 2026. Consequently, estimated property counts may change in the future once the new uplift values are taken into consideration.\r\n\r\nFor the Climate Change Defended scenario, an assumption has been made that the existing standard of protection of the flood defences keeps pace with climate change.","quality":"FRAW typically includes flooding from rivers with a catchment size greater than 3 square kilometres, and flooding from the sea (both along the open coast and tidal estuaries). Smaller watercourses with a catchment size smaller than 3 square kilometres are represented in the FRAW Surface Water data and maps.\n\nThe assessment takes into account the location and standard of protection afforded by flood defences and adjusts the risk categorisation accordingly from an initial, ‘undefended’ scenario.\n\nSome properties in Wales may be affected by more than one source of flooding, therefore when counting properties at risk, you need to be careful the same property isn’t counted more than once. For example, if a property is affected by all three sources of flooding, when reporting by flood sources it will be counted as one property for rivers, one for the sea and one for surface water & small watercourse. However, if you are counting the total number of properties in Wales at flood risk, using the sum of all three sources, the same property could be counted 3 times.\nThe property counts provided are a snapshot in time based on datasets from that year. They are subject to change year on year, as data and methodology improves over time. This may cause counts to increase or decrease between individual releases. When we count buildings or properties, this may include multiple buildings at the same address.\n\nIn 2024 Natural Resource Wales produced a projection for properties at risk of flooding for 2120 for the first time, which has been updated this year. The current 2120 projection is based on the 2025 figures. Both the 2024 and 2025 figures provide property counts that represent a defended scenario in 2120 (i.e. in approximately 100years time). These estimates are based on the same underlying assumption that the existing standard of protection of flood defences will be maintained in the future but have been calculated in two slightly different ways:\n \n1.\tFor the 2024 property counts, the future (2120) standard of protection of flood defences was set at 80% of the current standard. This meant that there was a reduction in the standard of protection meaning that some properties moved into higher risk bands.\n2.\tFor the 2025 property counts, the calculation has been performed differently. There has been no reduction in the standard of protection and the current level is maintained in the future (i.e. a flood defence providing a 100year standard of protection today provides the same 100year standard of protection in 2120).\n \nDifferences between the 2024 and 2025 property counts show how susceptible the figures are to change with only a slight alteration to approach underlying the uncertainty when making future predictions. \n \nThe assumption that flood defences will be maintained to the same level of protection is only one possible outcome. The risk assigned to properties in defended areas could change greatly in the future depending on the levels of investment and maintenance, further information can be found at Natural Resources Wales / Long-term Investment Requirements for Flood Defences in Wales.\n","rounding_description":"","reason":"Metadata update referring to revised allowances published by Welsh Government in March 2026."}],"rounding_applied":false,"update_frequency":{"update_type":"replacement"},"designation":"none","related_links":[{"id":"U0cOU","url":"https://naturalresources.wales/evidence-and-data/research-and-reports/flooding-reports-evidence-and-data/?lang=en","created_at":"2025-09-30T14:07:09.615Z","label_en":"Flooding reports, evidence and data","label_cy":"Llifogydd - adroddiadau, tystiolaeth a data"},{"id":"X5Pfg","url":"https://naturalresources.wales/evidence-and-data/research-and-reports/flooding-reports-evidence-and-data/long-term-investment-requirements-for-flood-defences-in-wales/?lang=en","created_at":"2025-09-30T14:17:09.434Z","label_en":"Long-term Investment Requirements for Flood Defences in Wales","label_cy":"Gofynion Buddsoddi Hirdymor ar gyfer Rheoli Perygl Llifogydd"}],"providers":[{"id":"a65a4c2b-cce0-440e-94a4-48d4c932b8d1","group_id":"79ba9763-728a-4794-9ade-4d022d1346d5","revision_id":"e8b90f36-114e-46bd-a95e-a7a6c3ad08b8","language":"cy-gb","provider_id":"071111f8-9931-43fb-bef9-a10165056a82","provider_name":"Cyfoeth Naturiol Cymru","source_id":"f322a690-001a-4c4a-b34a-cde9048cf4a1","source_name":"Data Cenedlaethol ar Asesu Risg Llifogydd","created_at":"2026-06-23T08:39:29.014Z"},{"id":"e1034a8c-383d-47b1-a56e-34cc6ec2cc57","group_id":"79ba9763-728a-4794-9ade-4d022d1346d5","revision_id":"e8b90f36-114e-46bd-a95e-a7a6c3ad08b8","language":"en-gb","provider_id":"071111f8-9931-43fb-bef9-a10165056a82","provider_name":"Natural Resources Wales","source_id":"f322a690-001a-4c4a-b34a-cde9048cf4a1","source_name":"National Flood Risk Assessment data","created_at":"2026-06-23T08:39:29.014Z"}],"topics":[{"id":23,"path":"23","name_en":"Environment, energy and agriculture","name_cy":"Amgylchedd, ynni ac amaethyddiaeth"},{"id":27,"path":"23.27","name_en":"Flooding","name_cy":"Llifogydd"}]},"publisher":{"group":{"id":"294afe5a-7ee2-472f-9d3c-802f8a8ebe38","name":"Environment","email":"stats.environment@gov.wales"},"organisation":{"id":"4ef4facf-c488-4837-a65b-e66d4b525965","name":"Welsh Government"}}}