Snow lysimeter runoff

The chart above shows the hourly runoff pattern from the snow lysimeters in the mature cedar and larch locations during mid-January to the end of February. There are many similarities, but also some interesting differences between the forest sites. All of the large peaks are associated with rain-on-snow events and these give similar runoff amounts for both locations.

The largest event starting on 11 February brought strong winds and rainfall of up to 4.5 mm/h, although temperatures remained only just above freezing point in the forest (larch site: 0.6 C, cedar site 0.2 C). With these cool temperatures we might assume the precipitation was snowfall, but the lysimeter runoff response shows a large peak that could only occur with rainfall. The local Murakami weather station nearer the coast shows a warm front moved in and temperatures rose to over 5 degrees Celsius.

In early February there are several small peaks at the cedar site which are not recorded at the larch site. This is most likely due to melting of intercepted snow in the cedar canopy.

The last two weeks of February show elevated levels of runoff (even night-time melting) due to rising temperatures and higher amounts of radiation in the energy balance. In this period we can see the runoff from the larch site generally exceeds that in the cedar site, where there is greater shading of the snowpack.

Snow survey

Mid-winter snow conditions at Takiya River today. Recent snowfalls have left large amounts of snow held in the forest canopy, but today temperatures reached 1-2 degrees Celsius, and so the snow in the canopy was melting and sliding off. The river channel shows no signs of any recent high flows. Mid-winter baseflow continues, and you can see large snow accumulation on the gravel bar to the right in the photo above.

Snow survey revealed that a significant amount of snow had accumulated since our last visit on 14 January. Snow depth at the larch site averaged 117cm, while the neighbouring cedar site had depths averaging only 79cm. This difference is due to interception and melt of snow in the cedar forest canopy, such as on days like today when temperatures are positive after snowfall. The relative snow density (compared to water) was around 0.31, and the snow water equivalents are given in the chart below. This is the depth of water that would result from the complete melting of the snowpack. So far this winter the snowpack size is moderately large, and the larch site has the most snow at 37cm of snow water equivalent.