Rain and snow calculating in SMBpdd

Schofield

Hi,
When I used SMBpdd, I was only required to input monthly precipitation. But the manual says rain and snowfall are separate. Is the precipitation is split into two parts by some parameters? What are these parameters?

Thanks.

joshcuzz

Hello,
Right now this is hardcoded, but precipitation is partioned between liquid and snowfall based on a cutoff temperature. Snow fraction is computed assuming a normal distribution for temperatures around monthly means with
solid fraction assumed for temperatures below 2C. You can play with the lapse rates to influence the surface temperature, but this cutoff temperature will dictate snowfall/liquid precip. partitioning. Let me know if this answers your question - happy to discuss more.
Josh

Schofield

Thanks for your reply!

I was confused that the manual says the the cutoff temperature is 0C. https://1drv.ms/u/s!AirnLPucqsivhwrK9gOMrSdM_82X?e=v0RR1f
Did I confuse the concepts snow and snow accumulation?

Another question is that whether the surface temperature is modified by the lapse rate automatically in transient run.

joshcuzz

Glad that helped! The surface temp. is updated automatically every step during the transient run. And thanks for pointing out that mistake in the manual. I didn't get to write that info, but will try and update it. I don't think you confused the snow and snow accumulation. If precip. is snow, it will accumulate. The snow fraction cutoff is 2C. And below that cutoff a fraction of the precipitation is assumed to be snow, similar to Synoptic Observations. Check out figure 2 here: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2008JD011208

Hope that helps.

Schofield

This really helped me helped me! Thank you very much!