The results of streamflow data analysis for 18mountain catchments in the Yana and Indigirka river basins (1966–2015)with the area from 16.6 to 89600 km² are presented. Theaverage 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%) inDecember on 12, 11, 9, and 7 rivers, respectively. Basically, thestreamflow variations are manifested in the form of abrupt shifts during1991–1996. There is a decrease in precipitation in winter (by 8–13 mm)and the absence of significant changes in the other seasons. An increasein average annual air temperature by 2.0°C led to an increase in theamount of liquid precipitation and streamflow in September by about 12mm. The revealed dependences of monthly streamflow on the amount ofliquid precipitation in September for small catchments (as well as thesingle period (1991–1996), when the simultaneous variations in thesehydrometeorological parameters are observed) indicate that the phasestate of precipitation is the main factor of changes in the low flow forthe analyzed rivers.