Synchronism of Variations in the Annual Runoff of the Largest Rivers in the Asian Part of Russia

The synchronism and asynchrony of variations in the annual runoff for the 18 largest rivers (153 river pairs) in the Asian part of Russia have been assessed using a novel original technique. The technique is based on taking three groups of river water discharge (low-, average-, and high-water years) into account and on the numeric rating of the runoff in the years compared. The runoff of the rivers is assigned to a particular group of water discharge by using its long-term average annual value. The years in which the runoff was less than 0.95 of its long-term average annual value are assigned to the low-water years; when it is more than 1.05, they are added to the high-water years. The average-water years include the runoff values from the 0.95–1.05 interval of the long-term average annual value. The runoff in the low-, average- and high-water years is identified by numbers 1, 2, and 3, respectively. A comparison of water discharges is made for all 153 pairs of river basins over the correlative observation periods under investigation. The years of identical water discharge (1–1, 2–2, 3–3) are assigned the number 1; the years with opposite water discharge (1–3, 3–1) are characterized by the number –1, and the years of similar water discharge (1–2, 2–1, 2–3, 3–2) are identified by the number 0.5. For each pair of rivers, the numeric sum expressed in fractions of the total period of observation is calculated, which is the parameter of synchronism (asynchrony) of runoff variations. For 18 pairs of the river basins, the values of the synchronism parameter are equal to or more than 0.5. For these pairs of the rivers, it is determined that the average contributions of the low-, high- and average-water years to synchronism are 45.1, 36.3, and 10.7%, respectively. The years of adjacent discharges increase the synchronism parameter by 29.2%, while the years with opposite discharges decrease synchronism by 21.3%. The synchronism is also assessed by using the correlation method.