I have always considered the idea impractical, in the in the event of a storm, you no longer have the use of a walking stick, unless anybody comes up with the idea of attaching an umbrella top to a 7 foot long hiking staff. Incidentally I was in the Hospital a couple of days ago and everybody but everybody was complementing me on my hand made forearm crutch. I could theoretically hold an umbrella in one hand, use the crutch in the other, and if you know how forearm crutches work, still have a hand free if I needed it in an emergency.
I guess it depends on how much you 'need' the stick for movement.
My uncle in law used to go to craft fares etc. with a large umbrella attached to his trusty walking stick with elastic bands which worked well for him. he needed the stick to walk any distance.
if a stick is helpful but not crucial then a combination would work