Improve Noah snow model treatment based on SNOTEL

Improve Noah snow model treatment based on SNOTEL data Michael Barlage, Fei Chen, Mukul Tewari, and Kyoko Ikeda

Snow modeling in Noah • Snow physics: – Currently one-layer snow model in Noah V 3. 0 (based on Koren et al. 1999, JGR) • Snow density change due to compaction, fractional snow cover, frozen-ground physics – 3 -layer model development by Guo-Yue Niu and Zong-Liang Yang at UT-Austin – Improving the one-layer snow model (work reported here) 2

Snow albedo comparison against 94 -95 Col de Port (France) data using Livneh’s albedo formulation Albedo Snow Depth Red: Obs, Black: V 3, Green: V 3 with albedo modification This new albedo scheme was used for Headwater simulations and released in WRF 3. 1

“Good” Sites: Coupled WRF Results WRF Precip WRF SWE Melt Obs SWE Sublimation 4

“Bad” Sites: Coupled WRF Results 5

Radiation Comparison: WRF terrain adjusted vs GOES SRB WRF SW is consistently higher than SRB for “bad” sites WRF solar at four points Good SWE sites GOES solar WRF solar at four points GOES solar Bad SWE sites 6

Major reasons for early snowmelt in Noah at “bad” sites • Higher downward solar radiation in WRF after adjusted to sub-grid terrain slope • High melt amount in early spring – Raise maximum snow albedo to 0. 85 • Sublimation in winter – Reduce surface exchange coefficient (Ch) for nocturnal stable regime – Reduce surface roughness length (Zo) based on snow depth and forest height

Effects of increasing maximum snow albedo Bad site Dash lines: Simulation with new max snow albedo Solid line: Default simulation Good site Legend legend LV: Livneh albedo ML: model level forcing 85: max albedo set to 0. 85 8

Effects of reducing snow-surface Zo and Ch for stable regime Bad site Dash lines: Simulation with reduced Zo and Ch Solid line: Default simulation Good site Legend legend LV: Livneh albedo ML: model level forcing ZE: Zo based on exposed veg 9 SL: Slater stability

New adjustment (in red) reduce Ch for stable regime Bad site Lower Ch in nighttime stable BL Good site BL is stable through most of days 2 - 5 Legend legend LV: Livneh albedo ML: model level forcing CH: WRF MYJ stability 10

Combined effects on long-term SWE Good sites Dash lines: Simulation with changes in Zo and albedo Solid line: Default simulation(contains new WRF Ch) By reducing sublimation and early spring melt, these mods delay snow melt Legend legend LV: Livneh albedo ML: model level forcing CH: WRF MYJ stability ZE: Zo = f(exposed veg) 85: Max albedo = 0. 85 11

Combined effects on long-term SWE bad sites Dash lines: Simulation with changes in Zo and albedo Solid line: Default simulation(contains new WRF Ch) By reducing sublimation and early spring melt, these mods improves timing of snow melt season Legend legend LV: Livneh albedo ML: model level forcing CH: WRF MYJ stability ZE: Zo = f(exposed veg) 85: Max albedo = 0. 85 12

Effects of observed SW Good sites Dash lines: Use of GOES SW as forcing Solid line: Control with WRF stability, albedo, Zo Legend legend LV: Livneh albedo ML: model level forcing CH: WRF MYJ stability ZE: Zo = f(exposed veg) 85: Max albedo = 0. 85 SW: GOES SW forcing 13

Effects of observed SW Bad sites Dash lines: Use of GOES SW as forcing Solid line: Control with WRF stability, albedo, Zo Legend legend LV: Livneh albedo ML: model level forcing CH: WRF MYJ stability ZE: Zo = f(exposed veg) 85: Max albedo = 0. 85 SW: GOES SW forcing 14

Combined effects with observed SW Good sites Dash lines: Simulation with changes in Zo, albedo, GOES Solid line: Default simulation(with new WRF Ch) By reducing sublimation and early spring melt, these mods delay snow melt Legend legend LV: Livneh albedo ML: model level forcing CH: WRF MYJ stability ZE: Zo = f(exposed veg) 85: Max albedo = 0. 85 SW: GOES SW forcing 15

Combined effects with observed SW Bad sites Dash lines: Simulation with changes in Zo, albedo, GOES Solid line: Default simulation(with new WRF Ch) By reducing sublimation and early spring melt, these mods improves timing of snow melt season Legend legend LV: Livneh albedo ML: model level forcing CH: WRF MYJ stability ZE: Zo = f(exposed veg) 85: Max albedo = 0. 85 SW: GOES SW forcing 16

Full grid effects of stability adjustment and all changes Left: Control Middle: Control + Ch Right: Control + Ch + albedo + Zo Effects are domainwide but increased time to melt does not propagate out of mountains Legend legend LV: Livneh albedo ML: model level forcing CH: WRF MYJ stability ZE: Zo = f(exposed veg) 85: Max albedo = 0. 85 SW: GOES SW forcing 17

Summary and Ongoing Work • Coupled WRF simulations produce early snowpack disappearance at many SNOTEL sites • We have a set of simple changes to the existing Noah which delays snowmelt and decreases sublimation • These changes include a stability adjustment and new Zo formulation that reduce sublimation and an albedo change that delays snowmelt • We are now running simulations over the full domain to do a more widespread and statistical comparison to SNOTEL sites

Site radiation 19