I would say the probable reason the lakes in the Sierra Nevada would be quite sensitive to climate changes because they occur in areas with extensive bedrock and little soil. The positive effect of soil especially if it is porous soil like sands and gravels is that it can be charged with groundwater that can then feed water bodies like lakes, whereas bedrock usually has much lower permeability than soil so can retain or contribute much less water especially in granitic bedrock like the Yosemites are composed of, for example..