The name La Niña originates from Spanish for "the girl", by analogy to El Niño, meaning "the boy". In the past, it was also called an anti-El Niño[1] and El Viejo, meaning "the old man."
From the excellent The Wizard and the Prophet: Two Remarkable Scientists and Their Dueling Visions to Shape Tomorrow's World by Charles C Mann:
Andean peoples had long known that every few years the coastal climate shifted dramatically, with warm downpours inundating the cold, dry coast. Because the rains usually began around Christmas, Peruvians referred to them as El Niño, a Spanish nickname for the Christ Child. In 1891 three Peruvians—an engineer, a geographer, and a naturalist—separately figured out how El Niños worked. During these times, the Humboldt Current abruptly weakens, allowing warm equatorial water to surge close to the coast; the warm water heats up the normally cold coastal air, which allows it to hold more moisture than usual, which, in turn, causes heavy rainfall on the desert shore. . . . a climatic system that extended across much of the Pacific and influenced the weather as far north as Canada. But the worst effects occurred in coastal Peru, where floods washed away railroads, wiped out farms, and destroyed power stations, blacking out cities. Thousands of “dead guano birds” were incidental damage. El Niño, Murphy said, “brings sickness and death to the population of the Humboldt Current.”
https://en.wikipedia.org/wiki/La_Ni%C3%B1a
From the excellent The Wizard and the Prophet: Two Remarkable Scientists and Their Dueling Visions to Shape Tomorrow's World by Charles C Mann:
Andean peoples had long known that every few years the coastal climate shifted dramatically, with warm downpours inundating the cold, dry coast. Because the rains usually began around Christmas, Peruvians referred to them as El Niño, a Spanish nickname for the Christ Child. In 1891 three Peruvians—an engineer, a geographer, and a naturalist—separately figured out how El Niños worked. During these times, the Humboldt Current abruptly weakens, allowing warm equatorial water to surge close to the coast; the warm water heats up the normally cold coastal air, which allows it to hold more moisture than usual, which, in turn, causes heavy rainfall on the desert shore. . . . a climatic system that extended across much of the Pacific and influenced the weather as far north as Canada. But the worst effects occurred in coastal Peru, where floods washed away railroads, wiped out farms, and destroyed power stations, blacking out cities. Thousands of “dead guano birds” were incidental damage. El Niño, Murphy said, “brings sickness and death to the population of the Humboldt Current.”
https://www.amazon.com/Wizard-Prophet-Remarkable-Scientists-...