It might be worth experimenting with some of the cooling vest technology available for military, industrial, athletic and medical applications. This thread had me contemplating whether I could run longer if I could maintain a lower core temperature. So I started looking at some of the passive and active cooling systems out there. The most elaborate have circulating ice water with battery pump and backpack reservoir - intriguing but impractical. Some of the gel pack or ice pack insert vests might work in a climate like the OP faces for some users and uses. Would be worth experimenting with.