A rare deluge of rainfall left blue lagoons of water amid the palm trees and sand dunes of the Sahara desert, nourishing some of its driest regions with more water than they had seen in decades. Southeastern Morocco’s desert is among the most arid places on earth and rarely experiences rain in late summer. The Moroccan government said two days of rainfall in September exceeded yearly averages in several areas that see less than 250 millimetres annually, including Tata, one of the areas hit hardest. More than 100 millimetres of rain were recorded in Tagounite, a village about 280 miles...