Strengths: An original analysis, making good use of linear time series methods.
Points for consideration:
“300 million residences of Detroit” should perhaps be 300 thousand?
Phase is reasonably stable at frequecies of substantial coherence, and can be interpreted in those regions.
Could look at cross-correlation after deseasonalizing: the seasonal relationships and non-seasonal relationships may have different information.
The interpretation of correlation between inflow and outflow as a measure of successful control is unclear.