I agree it's getting too much sun, and you might want to consider adding organic matter to the sand as well. But I found this which might be helpful:
An elephant ear that is in a climate that is outside and thriving all year will tend to shed its lower leaves during the year and much more in fall. The lower leaves turn yellow and fall off or just droop to the ground.
In an environment where the bulb will go dormant in the winter, this tends to happen as the plant shuts down for the winter. The leaves turn a paler green, then yellow, then bright yellow and droop and fall to the ground.
These leaves can be picked off and disposed of if they are unsightly.
http://www.emilycompost.com/el...
And in your climate, chances are once it gets some shade, new growth will start right away.
Also,
@LariAnn might have an answer, she moderates the Aroids Forum.
