Q.Fig Tree Leaves
I am located in Southern California high desert. My fig tree is loaded with green figs. Suddenly after a heat wave, many of the leaves have turned yellow and are dropping off. Is this something to be concerned about? Could it be underwatering?

In this case I would say watering is the likely reason for the yellowing of leaves.
Increase the water for your Fig, in a warm climate your tree needs to be watered deeply once a week.
https://www.gardeningknowhow.com/edible/fruits/figs/fig-with-yellow-leaves.htm