Something we can glean from the various adventures and novels in Tyr, is that Under-Tyr has fairly extensive sewers and tunnels. Water in the setting always seems to rely on a local spring or aquifer by means of direct drawing through wells and pumps. That’s all well and good, and would certainly be done, but there is a method of irrigation and cooling that I’m shocked to say has not even been mentioned on this site once by my search yesterday! That is, the Qanat! Qanat - Wikipedia
A long tunnel punctuated by vertical venting shafts, these are dug by specialized teams into hills and mountains to access the higher water table and bring water out of the otherwise underutilized mountain watershed. Essentially, they are long underground aqueducts that can be attached to agriculture, homes, or other works. A building with a connection to the Qanat tunnel and a wind tower may utilize a form of evaporative cooling to draw air through the tunnels, cooling it up to 59F/15C compared to outdoor temperatures and providing a pleasantly damp basement in the arid desert climate. They’ve been in use for at least 1000 years on Earth.
These sort of evaporative cooling systems can be so effective a to create ice-boxes, and have been utilized in this method even longer than Qanats, with records as far back as 400BCE attesting to these structures Yakhchāl - Wikipedia
The cities may already utilize this sort of technology, but it would be a great addition to any druid’s arsenal in restoring Athas if it is not yet in use!