18 April Rain-on-snow Event

 

In the stage hydrograph above you can see the moderate size flood caused by a rain-on-snow event during 17-19 April. You can also see the typical diurnal snowmelt runoff pattern which looks like a sine-wave with a steep rise and more gradual fall in water level each day. For Takane Amedas gauge, daily precipitation was 79 mm on 18 April with maximum intensity of 12.5 mm/h. Warm temperatures up to 13.4 degrees Celsius were measured in Murakami, with peak wind speeds of up to 21 m/s causing significant sensible heat transfer to the mountain snowpack. Total event precipitation was 105.5 mm at Takane.

However, today we visited Takiya River under perfect blue sky conditions for our survey and discharge measurement. The following photos show the discharge measurement and channel features around the gauging reach.

Winter season runoff

Stage = 0.545m, Q = 2.02m3/s

 Today we downloaded the stage data since December 2020. We can see there are many peaks during the winter and early spring season due to rain and rain-on-snow events which occur with warmer temperatures. Similar to the previous winter, we had some record-breaking warm temperatures, and snowpack was below average. January 2021 received snowfall, but February was much warmer than average (7th warmest in record), and March was the warmest on record. We can see that snowmelt has really progressed during March. Precipitation was well above average during January to March.

River stage during winter of 2021

River stage during winter of 2020

The table below highlights the recent record warm temperatures recorded in March for Murakami Amedas station. The last three years are all in the top 4.

Rank    March mean temp.    Year

                    (Celsius)

  1                    7.3                    2021

  2                    7.0                    2020

  3                    6.3                    2002

  4                    6.0                    2019

  5                    5.9                    2015

(Data since 1979)