DENIS DUMO  SEVERE flooding in South Sudan has forced more than 600,000 people to flee their homes since July, the United Nations said, after months of torrential rains caused the Nile to burst its banks. The impoverished East African nation is struggling to recover from a five-year civil war and was already suffering severe food shortages. Scientists say the unusual rains are caused by a cyclical weather pattern that has been exacerbated by climate change. The coronavirus pandemic is also complicating the response, said United Nations humanitarian coordinator for South Sudan Alain Noudéhou. Costs for delivering aid have risen with…