The shrinking reservoirs are the immediate result of record-low snowpack this winter, which was erased by record heat in the spring. Melted snowpack creates most of the Colorado’s flow during the dry summer months. But as the Southwestern climate has grown hotter and drier, the river’s flow has become smaller and less reliable.
Legitimate question: I can understand that record-low snowpack would cause less water to flow into the lake, but the "erasure" of the snow pack by heat is just melting that would be captured in the lake, right? So if the record-low snowpack had been followed by record cold, would we have even less water in the lake?