Hash rate bottomed Dec 17-18th soon after Joseph Lubin of ETH stated the bottom is in look at the chart yourself its back on a growth trajectory;

https://etherscan.io/chart/hashrate

The hashrate of ETH is either caused by the rapid expansion and growth of the ETH mining sector or the expectations of investors in the cryptocurrency market that major digital assets will soon recover from their drops. The reduction from 3 to 2 mining reward for ETH should accelerate upside price on the upgrade Jan 15-16th.