Gushing downpours finally arrived in California last month, when December rains brought some relief to a landscape parched after three years of severe drought. But the rain came too late for thousands of Chinook salmon that spawned this summer and fall in the northern Central Valley. The Sacramento River, running lower than usual under the scorching sun, warmed into the low 60s — a temperature range that can be lethal to fertilized Chinook, the largest species of Pacific salmon, need cool waters to reproduce.