Spain has the greatest frost hazard of all major citrus growing regions of the world. Frost will continue to limit Spain's potential for expanded production. In the past 40 years Spain has had 8 severe tree damaging freezes and many more fruit damaging frosts. - Millet (1,167-)

Maybe it is that cold weather that makes Spanish clementines the best tasting--just my opinion on the taste of the ones I have tried.