my theory is that their wandering roots run deep and wide when planted in the field, which equates to full hydration in areas with much higher rainfall than deserts, i.e. surface soil dries up so much faster, which may falsely indicate drying out, when in fact the deeper roots and surrounding soil are still soaking wet.
in potted conditions, we could literally wait until the pot gets really light, or at the early stage when the leaves start getting droopy–before watering again.
jujus actually use their fruits as water reservoirs. Fruits get wrinkly and prune-like in hot and dry conditions, before the leaves start getting droopy. From a survival standpoint, we could conclude they have a ‘biological need’ for their fruits in dry conditions, and when there’s a need, there must be a physiologic incentive to produce them, as well as a need to hold on to them–preventing fruit drop.
fruits will shrivel and drop off in times of severe drought, but this is only when the plant does not get watered soon enough. Thankfully we seem to be able to water them just in time before fruits drop in en masse. And by doing so, the trees seem to respond by holding on to the fruits more ‘dearly’ 
we had 115F weather yesterday, and the first pic shows a couple of black sea juju fruits wrinkled as if beyond resuscitation.
the next picture shows the same fruits the day after(today), status post irrigation. The top juju even produced the typical ‘anthocyanin blush’ sunscreen, practically overnight.
and the same fruits were quite capable of doing it over and over, as long as the trees are watered soon enough. Here are two successive pics on days we were late(again) in watering them, more than two weeks ago
