the year-long cycle of the development of hydrologic processes. Where the climate is temperate (in the USSR), October 1 or November 1 is conventionally taken as the beginning of this cycle, in contrast to the ordinary calendar year; the hydrologic winter half-year is counted from October 1 (or November 1) to March 31 (or April 30), and the summer half-year from April 1 (or May 1) to September 30 (or October 31). The hydrologic year has been introduced in order to obtain a better correspondence between runoff and precipitation, since under calendar time runoff and precipitation do not correspond to each other. Groundwater resources in most of the USSR are smaller at the end of the winter, and at this time the snow supply is substantial. Standard processing and publication of hydro-logic materials in the USSR is done by calendar years.
A. I. CHEBOTAREV