Severe weather events and transportation disrupting natural disasters are on the rise, and the only thing that we can be sure of is they are going to keep coming fast and furious in the near future. We don’t know when, where, or what extent the impact will have, but we know it’s coming.

The resulting disruptions to your supply chain will last days, weeks, or months. And if the part of your supply chain that is disrupted is one supplying a critical component that is sole-sourced or in a supply shortage, any and all products it is used in will be in jeopardy once the inventory runs out. As a result, JiT inventory is becoming a thing of the past. However, too much inventory on hand is NOT a good thing. You want a balance between JiT and everything you need for the planned production run. And that balance could be anywhere from a few extra days (for inventory that can be obtained from another source on short notice) to a a few months (for something otherwise hard to get).

But how do you figure out the right stock levels? It’s not just rarity. After all, stock costs money and ties up working capital … capital that likely has better uses. After all, early supplier payments can bring cost reductions. Investments can bring recurring cast. R&D can develop new, more profitable, products for sale. And so on.

So how do you determine the right level of safety stock? Expand the working capital optimization model to allow for a variable disruption cost based upon variable stock levels, each of which has an associated investment cost (in the form of tied up working capital), and determine the stock levels from the investment that optimizes working capital.

Again, the right level of safety stock falls out of working capital optimization.