Many have been warning since last fall that winter is coming for unprofitable, venture-backed startups. It is now becoming increasingly obvious that the season of investors refusing to fund these self-immolating ventures is here. The New York Times reported on 30 startups around the world that have eliminated over 8,000 jobs in the last four months.

Funding for startups may also be harder to find. The National Venture Capital Association reported that 2,215 U.S. startups raised money in the last quarter of 2019, which was the lowest since late 2016, according to the New York Times. I've seen for myself that venture capitalists will tell money-losing startups to get profitable before they're willing to invest more.

What's behind the current VC winter is the same thing that caused the one in 2016 -- a series of unsuccessful initial public offerings of money-losing ventures. For example, Uber and Lyft have disappointed investors. And WeWork was unable to go public -- it famously suffered an 80 percent plunge in its value between last January and November.

VCs are not signing up to lose more money by investing more in money-losing portfolio companies. As the Times noted, layoffs of unprotifable ventures are "starting to come in droves." Examples include the over 500 who lost their jobs at robot pizza startup Zume -- which had raised a whopping $400 million in capital -- and car-sharing company Getaround.

If you lead an unprofitable startup, its survival depends on how you respond to this VC winter. Here are the four most important things you must do in the next two weeks to boost your company's odds of survival.

Build a detailed monthly cash flow model.

If you do not have a monthly cash flow model, you need to build one immediately. The reason is simple -- you can no longer rely on outside sources of funding to keep your venture going. Instead you must boost cash inflows and cut cash outflows until your venture can fund itself.

As someone who has built many such cash flow models, the most important part of the model is to collect detailed, accurate data on your company's cash sources -- such as revenues -- and uses -- such as rent, payroll, utiliities, legal fees, travel, and training.

If  you employ a good chief financial officer, these data should be easy to assemble. If not, you may need to hire an outside expert to come in to your company to build such a model. And once you have it in place, develop a 12 month cash flow forecast which will help you figure out how how long it will take to consume your remaining cash.

Identify and apply a tourniquet to your biggest cash bleeds. 

The cash flow forecast should strike fear in your heart. For example, if you have only enough cash to last for six months, you must calm down and look closely at where you can stop the bleeding right away to extend the life of your startup.

Are you renting expensive real estate? If so, try to find less-expensive space and figure out whether you can cancel your lease (or find another tenant to take the lease off your hands). Do you employ high-salary people who are not contributing enough to your short-term survival? They may be candidates for a layoff. And if you have an expensive customer conference planned for the next few months, you might consider whether to cancel it this year.

Close deals with the best sources of new revenue.

While you are cutting off your biggest cash bleeders, examine the list of prospective deals to bring in new revenue. Is the timing and amount of cash flow to your company from these deals accurately reflected in your cash flow forecast? If so, are these forecasts realistic? If not, change the forecast accordingly.

Consider whether you can take action -- such as changing the staffing on the most promising deals or offering creative financing terms -- to increase the likelihood of turning high potential deals into near-term cash inflows. In addition, brainstorm with your leadership team to identify potential new sources of revenue that you may not have considered.

Evaluate strategic alternatives.

If, after all these efforts, you have a clear path to profitability, you should turn your attention to growth. If not, you should search for an acquirer or possibly partners to which you can license your technology in exchange for life-saving cash.

Eventually, the VC winter will end. To keep your unprofitable venture going until then, do these four things now.