Spring rain-on-snow

First major rain-on-snow event of the season. Stage = 95cm, water temp. = 5.3C.

Warm temperatures up to 11.6 C and intense rain showers (3.5 mm/h) through the night and during the morning of the 19th led to typical rain-on-snow conditions and a moderately high discharge in Takiya River (stage about 1m).

Two students and I completed a snow survey of three locations (deciduous larch, mature cedar, and open paddy field). The snow pack beneath the mature cedar remained much firmer and more icy compared to the other two sites, which can be explained by the different energy balance between sites. During such rain-on-snow events we would expect the net radiation balance and the energy brought by warm winds to be greater in the open and deciduous larch sites.

The larch site had the highest snow water equivalent (SWE) and the greatest snow depth. The paddy and mature cedar site had similar SWE, but the depth was less and the density higher in the paddy where liquid water content was particularly high at the base of the snow pack.

Snow depths (cm)
Paddy: 52
Cedar: 72
Larch: 88

Snow survey in the larch site

Late winter

Snowmelt water is crystal clear. Stage = 58cm.

Takiya River stage hydrograph (Nov 2012 to Mar 2013)

Today I serviced all the snow lysimeters, and also downloaded the river water level data enabling me to plot the stage hydrograph for the entire winter season as above. This winter is notable for the absence of any large rain-on-snow events during January and February as cold conditions continued. Precipitation is predominantly snow from mid-December to the end of February. Warmer conditions early March have given two moderate peaks already. Interestingly, the winter minimum low flow of about 40cm stage is roughly the same as the summer low flow stage of last September. Generally we expect the winter low flow to be a little higher due to basal melt of the snowpack and minimal ET during winter.

We are just about to enter the snowmelt season, and mountain snowpacks reach their peak during the month of March, at least in the Takiya River catchment. I was surprised to see that the water level was already a little high at 58cm - likely due to rain-on-snow over the previous weekend, though a trace of new snow had also fallen.

Early this morning temperatures plummeted to -6.5 degrees C for the tributary young cedar site (coldest temperature recorded there all winter). Must have been even colder in the valley bottoms. Clear skies, low humidity and still conditions gave extreme radiative cooling overnight, but warm air moved in during the day and temperatures reached the teens. However, in the shady spots the snowpack remained frozen solid all day. Lots of fresh monkey tracks in the snow.

Larch lysimeter

Mature cedar lysimeter

Young cedar lysimeter

View towards Japan Sea (left) and Miomote River (centre) at about 300m asl

Same viewpoint looking north across lower part of Takiya catchment (right-hand peak about 640m asl)