Start of the rainy season

Stage = 0.345m, Discharge = 0.422 m3/s

The stage hydrographs above show the past two weeks (upper) and the past six months (lower). We have already had some heavy rain marking the start of the rainy season. The lower graph shows the high flows during winter compared to the low flows during April and May and into June. We cannot see the usual pattern of snowmelt runoff during March to May, due to the almost total absence of snowpack this year.

Record low runoff for May

Stage = 0.336 m, Discharge = 0.352 m3/s

At a first glance today's discharge appears typical of early summer low flow conditions. However, May was much drier than normal with only 96 mm of precipitation (Miomote Amedas) compared to the 30-year average of 150 mm. In addition, we have just experienced record low snowpack for this past winter. The lack of precipitation during May, combined with the lack of snowmelt runoff, have produced the lowest recorded basin runoff for the month of May at just 111 mm (20-year average is 287 mm).

This follows directly after the record low runoff for April, and both these records can be attributed to the record warm temperatures and record low snowfalls this past winter.

Depending on the timing of the rainy season later this month, and the amount of rain it brings, we could be expecting record low flow conditions for many basins in Niigata region and other parts of Japan.