You forgot to include their actual analysis (which is too long to repost here) and conclusion...
"Overall we conclude that, while there is no reason to doubt that the 2006/07–2008/09 drought did increase migration from northeast Syria during 2008–09, FGK significantly overstate both the scale of the migration, and the extent to which it was caused by drought. The official UN and Syrian government estimate was that 40–60,000 families migrated from northeast Syria during 2008–09, not the 1.5 or 2 million people that is often claimed. Moreover, given that large-scale migration from northeast Syria predated the drought, it follows that ‘excess migration’ (i.e. migration during 2008–09 minus average pre-drought migration numbers) must have been lower still. Numbers aside, we also find that FGK present a mistakenly environment- and drought-centric reading of the causes of northeast Syria's agrarian and migration crisis, and that other factors, most importantly Syria's experiment with economic liberalisation, were likely more important contexts for and catalysts of migration than the drought."
And then the rest that you left out, which includes the actual analysis of the data...
"Clearly, such comments should not be dismissed as irrelevant, since subjective representations and reasoning are critical elements in the descent into war, as in any political process. That said, it is striking how little personal testimony is marshalled in support of the claim that drought-related migration was a factor in the Syrian uprising: Kelley et al. quote just one displaced Syrian farmer, Gleick and Femia and Werrell none at all...
In summary, the evidence marshalled by FGK and others in support of drought migration-civil war thesis is extremely weak: neither their assertions about population pressures, nor their claims about the chronology and geography of Syria's early unrest, nor indeed the testimonies they quote, provide any firm basis for concluding that migration from northeast Syria was a factor in civil war onset. To the contrary, our evidence suggests that migrants from the northeast were not significantly involved in the early 2011 unrest."