Record low runoff for April

The provisional estimate for April runoff is just 240 mm, which is a record low by a large margin.

April runoff is very important as in almost every year April runoff is the greatest of any month, and it coincides with the planting of the rice paddies at the end of April to early May when demand for agricultural water resources is high.

Year    April runoff (mm)      Comment
2020          240                       Lowest on record (since 2001)
2019          348                       2nd lowest on record
2018          617                       4th highest on record
Note: Average April runoff (2001-2019) is 500 mm.

The table above shows April runoff for the last three years. The two lowest April runoff values have occurred in the last two years, and this year's record low is a full 108 mm lower than the previous record low, and less than half the average value of 500 mm.

Lack of seasonal snowpack is the main reason for these low April flows. April precipitation was actually a little above average at both Miomote and Takane (168mm/198mm compared to averages of 149mm/171mm respectively) and so cannot explain these low flows.