Winter hydrograph pattern

The above hydrograph shows the usual winter pattern when autumn rains decrease through the end of the year as temperatures drop and precipitation decreases or changes to snow. We can see that after January 8th, the streamflow levels are mostly decreasing until the moderately-sized peak on the 26th. The long period of decreasing flows in January indicates that temperatures have been cold with little or no rainfall until the 26th. However, it has mostly been dry and cold without snow in the Niigata region, and snowpack levels remain extremely low. The rain-on-snow peak flow on the 26th was caused by daily rainfall of 26.5mm (maximum intensities of 4.5mm/h), and temperatures reaching 8-9 degrees C leading to some snowmelt.

In the photos below we are doing snow survey to measure the snow depth and snow water equivalent in locations where we have also installed snow lysimeters. Snow depths are very low this year, with only about 55cm at the larch site, 35cm at the mature cedar site, and anywhere between 30 and 82cm at the young cedar site which has very uneven snow depths due to the canopy interception processes.

Snow survey at the larch site (depth = 55cm)

Snow survey at the young cedar site (depth = 30-82cm)

Larch site lysimeter, with relatively uniform snow depth

Mature cedar site lysimeter, with outline of lysimeter trays visible

Young cedar site lysimeter showing the mounding of the snow between the trees, with very shallow depths close to the tree trunks

Where is the snow this year?

Very little snow so far this winter season. We could be heading for the least snowpack in over 10 years! Conditions were mild and relatively dry during end of December to early January when we usually expect the first heavy snows of winter.

Today we did snow survey at the three snow lysimeter locations. The mature cedar location (shown above) had a snow depth of only about 10 cm, while the neighbouring larch stand had a depth of about 30 cm, showing the influence of the snow interception processes such as canopy melt-drip in the cedar forest stand. During mild conditions, the intercepted snow in the cedar stand is soon melted, while the snow tends to accumulate in the larch stand where there is very little snow interception.