Theresults of streamflow data analysis for 18 mountain catchments in the Yana and Indigirka river basins (1966-2015) with the area from 16.6 to 89600 km2 are presented.The average streamflow increased by 13 mm (54%) is September, by 1.5 mm (57%) in October, by 0.4 mm (59%) in November, and by 0.1 mm (80%) in December on 12, 11, 9, and 7 rivers, respectively. Basically, the streamflow variations are manifested in the form of abrupt shifts during 1991-1996. There is a decrease in precipitation in winter (by 8-13 mm) and the absence of significant changes in the other seasons. An increase in average annual air temperature by 2.0°C led to an increase in the amount of liquid precipitation and streamflow in September by about 12 mm. The revealed dependences of monthly streamflow on the amount of liquid precipitation in September for small catchments (as well as the single period (1991-1996), when the simultaneous variations in these hydrometeorological parameters are observed) indicate that the phase sta
