If anyone is interested in the refugee/IDP thing, here is a UNHCR report on the demographics of Syrian refugees from before Trump wrote his sternly worded letter.
UNHCR: Situation Syria Regional Refugee Response
And I haven’t seen anything comprehensive from the Red Crescent or the like; just stuff like this:
The RIC, though, has a report on the current crisis:
RIC (Report): Erdogan’s “security zone”: Refugees and humanitarian aid in North East Syria
This report seeks to provide an analysis of the Turkey’s current invasion in terms of its humanitarian impact. We examine Erdogan’s stated reasons for the invasion of North and East Syria, including his proposals for a so-called “security zone” in which to resettle refugees. We also assess the ongoing humanitarian impact of the invasion, as well as analysing the long term impact of the invasion on the stability and security of the region.