About $2 billion in urgent aid is needed this year to alleviate the suffering of the most vulnerable victims of Yemen’s civil war, or about 10 million of the country’s 27 million people, the resident U.N. humanitarian chief said Tuesday. The Arab world’s poorest country has been in the grip of a civil war since 2014, when Shi’ite Houthi rebels and allied forces swept down from the north and captured the capital, Sanaa.