Warming springtime temperatures in California are expected to accelerate melting of the state’s record snowpack, sending water surging down a major river in Yosemite National Park that could overflow its banks, officials said Monday.Reservoirs downstream from the Sierra Nevada have been lowered in anticipation of the heavier-than-normal runoff, said reservoirs managers. The current snowpack is double its normal size.The snowmelt flows downhill during warm months into reservoirs and canals, which supply one-third of the water used by residents of the most populous U.S. state. It also irrigates crops in the nation’s most productive farming state.