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?

In the mountain west warm dry springs coincide with higher winds. The blowing warm dry air leads to dramatically increased evaporation of snow melt, drying of soil, as well as increased transpiration in plants, so the total moisture loss is much higher than what you might expect simply from modeling simple heat evaporation of open water bodies.

university of utah has several studies on the matter. a substantial percentage of the snowpack sublimates during a heatwave, never has a chance to melt. Of the remaining snowmelt, it has to saturate the ground before any can flow to an adjacent stream to feed the water table, and the bone dry soil around here can absorb a significant amount of water.

Not all of the erasure is captured. For example, if the ground is dry, than most gets absorbed into soil and won’t make it to the river. Or the snow may sublimate and go straight to vapor at heat.

Record cold would lead to more water. It would melt out fast later and since the soil was already recharged it would flow to rivers.

Worth noting this is generally glacier free landscape so the snow melts fully each year.

Aside from melting at historically fast levels, the snow itself is at record low levels. Less snow -> less snowpack -> less water.

For data, check out the second visualization here:

https://www.wcc.nrcs.usda.gov/ftpref/support/states/CO/produ...

There's no snowpack left, earlier in the season, because there's way less snow, and it's being consumed faster.