Gwyntoedd cryfion a thonnau mawr ynghyd â llanw uwch na’r cyffredin a achosodd y llifogydd ar y ddau achlysur. Ym mis Rhagfyr cafwyd y llanw uchaf ym Mae Lerpwl ers gosod mesuryddion llanw yno 21 mlynedd yn ôl. Ym mis Ionawr, roedd  lefel y môr yn Aberdaugleddau, Casnewydd ac Abermaw yn uwch nag a gofnodwyd ers 1997.
Both flood incidents were caused as a result of a storm surge and high winds combining with high tides.  In December, the peak sea level recorded in Liverpool Bay was the highest recorded in the 21 years since tidal gauges were established.  The January peak levels recorded at Milford Haven, Newport and Barmouth were the highest recorded since 1997.