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Runoff Report 1999..... Night-Time Temperatures
This report already referred to and described many time the effect of the temperatures on the runoff. To avoid repeating myself I will keep this section brief. Temperatures during the night are always colder than at daytime. Lower temperatures mean slower melting process. The water mass produced during the night therefore is always smaller than at day. After the snowpack retreats to higher altitudes the temperatures during the night are getting too low for continuing the melting process. The water supply gets interrupted. I described that already in more detail earlier in this report. As for the 1999 runoff, the night temperatures during the first stage were mostly as low as the freezing point. The largest portion of the low altitude snowpack melted only during daytime. This effect explains the differences between day and night lake level increases. The unfrozen soil acted as a form of buffer and allowed a subsurface flow, slowing down the total water flow. The water produced at day was partially stored in the ground and continued flowing throughout the night. The subsurface pressure slowly decreased leading to a reduced flow into the watershed. This effect continued throughout the remaining runoff. The night temperatures were higher, but the snowpack has retreated to higher elevations, too. And higher altitudes equal lower temperatures. The power of the sun during the 1999 runoff was never strong and lasting enough to considerately heat up the ground, which could have effected the melting process at nighttime.
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