Figure 2.2: Number of IDPs and refugees in and from Syria, 2009 to 2016 Source: IDMC, with UNHCR and UNRWA for refugee data (2016 figures not yet available) observed, a type of circular cross-border displacement. This occurs when people flee back and forth in response to the ebb and flow of hostilities, particularly when they take place close to borders or are part of regional conflicts in countries with a number of borders.189 In north-east Nigeria and the wider Lake Chad basin, displaced people cross the border repeatedly to escape attacks by Boko Haram and heavy-handed military operations against the group.190 One family had to flee within Nigeria and across the border to Cameroon and back seven times in 18 months.191 In east and central Africa, porous borders and a lack of coordination between countries have facilitated circular cross-border displacement, with people moving back and forth between the Central African Republic (CAR), DRC, South Sudan and Sudan when they are unable to find safety (see South Sudan spotlight). The four countries were hosting 7.8 million people uprooted by conflict and violence as of the end of 2016 – almost one in five IDPs worldwide. As of September 2016, more than 660,000 refugees from the four countries were living in one of the others.192 In the absence of systematic monitoring it is difficult to assess the extent to which such patterns are generalised, but there is a consensus that displacement is often a complex process involving more than one episode. The onward trajectory of an IDP, as with other people on the move, depends on a number of factors ranging from the location of friends and relatives to the accessibility of safe areas.194 For people displaced various times internally before fleeing abroad and those caught up in circular displacement, each new movement depletes their resources further, deepens their impoverishment, creates new vulnerabilities and makes existing ones worse.195 In countries already struggling to meet their IDPs’ needs, an influx of refugees risks triggering a vicious cycle of population movements within and across borders, as resources wane and tensions rise across the region. Violence in host countries in central and eastern Africa has also forced refugees back inside their own borders, putting them at risk of becoming internally displaced upon their return.193 56 GRID 2017 56