Snowmelt-runoff in low mountains of the Upper Ob basin (by the example of a small low-mountain Maima catchment)

For analysis of a snowmelt runoff of the low-mountain Maima catchment (Russian Altai) we used the daily data from the Kyzyl-Ozek weather station (air temperature, precipitation), the Maima gauge (water discharge) for 1997-2017 and the data on snow measurement works (2015-2017). Dynamics of major climatic parameters of winter (air temperature, precipitation) and characteristics of floods over the period of observations (since 1939) were studied. Hydrometeorological processes of spring snowmelt (1997-2017) were analyzed, and flood flow hydrographs with specified melt, rain and ground water were constructed and analyzed as well. The linear dependence (correlation coefficient: 0,84) of snowmelt runoff depth and total solid precipitation for the cold period was obtained. A quantitative assessment of heat and cold waves responsible for a timeframe and intensity of snowmelt was performed. The analysis of dynamics of water discharge caused by rainfalls after the beginning of snow cover melt as well as characteristics of heat and cold waves made it possible to estimate the time lag of melt- and rainwater to the river network during the high water period (1-2 days). Maximum discharge (20,6-110 m³/s) usually occurred after rise in average daily temperature above 20 ^oC, or it was associated with heavy rains. On average, the peak of high water was observed in 24 days after its beginning. In the Maima basin and in Altai as a whole, the rise in temperature and reduction in precipitation amount during the cold period was recorded for the whole period of observation (since 1939). During the cold period of 1997-2017, precipitation increased slightly, while average temperature-by 0.7 °C. Due to climate changes, a shift in dates of high water and maximum discharges occurred 5-6 days earlier in 1997-2017, as compared to 1940-1975 (before sharp warming onset in the region). This was due to temperature rise and reduced cold period. A significant change in intra-annual distribution of runoff (i.e. reduction in share of flood runoff in annual runoff from 49.2 to 36%) was noted. From the beginning of observations, annual runoff, total runoff depth for the flood period and maximum flood discharge fell by 3.5%, 28.8% and 31.8%, respectively. Using the snow survey data (20152017), we assessed the meltwater role in the formation of flood and annual runoff. The share of snowmelt runoff in annual one ranged from 27 to 41%. The coefficient of meltwater runoff made up 0,59-0,81 thus correlating well with the previously obtained data for other Altai rivers. Maximum snowmelt runoff (0.81) was marked in the spring of 2016 after a snowless winter. This was induced by greater soil freezing and less infiltration loss of snowmelt runoff. In the period of high water recession, the coefficients of rain flood-induced runoff were 3-3,5 times lower showing less changeability.

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