Storm Daniel developed in the early days of September in Greece, causing serious flooding on 5-6 September before strengthening as it moved across the Mediterranean to northeast Libya over last weekend.
September is normally a dry month in Libya’s Jebel Akhdar mountains around the coastal city of Derna, averaging just 1.5 millimetres of rain, but this week the area received a deluge of around 400 millimetres in just 24 hours.
As the massive run-off accumulated in the mountains, water levels rose alarmingly along Wadi Derna, which eventually runs through Derna to the sea. It overwhelmed a small dam about 20 kilometres south of Derna, before the torrent gathered speed and strength as it moved down towards the city. It burst over the 20-metre-high Derna waterfalls, seven kilometres out, and then reached the city outskirts as a huge torrent before hitting and breaching a much larger dam.
