On the Effect of Intermittent Nonstationarity of Long-Term Changes in the River Runoff

Based on the analysis of 162 longest (more than 100 years each) series of annual, maximal, and minimal runoff in rivers of different genetic types, the regularities of changes in the degree of stationarity/nonstationarity of the runoff changes are studied. It is shown that changes in the average annual and maximum runoff in the rivers of the "main" type-non-effluent, unregulated, as well as in the rivers of glacial feeding-throughout the period of observations generally correspond to the stationarity hypothesis. On the contrary, for a significant part of the runoff series of all types of effluents and regulated rivers, as well as the minimum flow of rivers of the main type, the alternation of segments of realizations of stationary and non-stationary processes with respect to mathematical expectation, is typical. To describe this effect, we propose the concept of "intermittent" nonstationarity. The nonstationarity parameters of the indicated type are compared with the nonstationarity parameters of the monotonous type.