I'm from Portugal and I'm keeping several tanganyika species in a pond. They are still there currently, but I'm planning in bringing them in by the end of the October.
During summer, and late spring, my biggest concern is the temperature delta between day and night and the fact that during a really hot day the temperature can reach 30ºC.
It's the first year I'm doing this and it's working as planned. There are other's here in Portugal that keep cichlids in ponds, some tropical, only through summer or inside greenhouses, or all year round with sub-tropical like from Uruguay.