With customer traffic sagging, U.S. retail landlords are using their sprawling concrete fields to host carnivals, concerts, and food truck festivals. A large event can generate $60,000 for a landlord in a week, says event producer KevaWorks Inc. Events bring “additional traffic and also encourage people to stick around longer,” says Lisa Harper, senior director for specialty leasing at CBL & Associates Properties Inc. That’s a much welcome boon after a 20 percent decline in shares of publicly traded mall landlords in the past year.