4.5 Streamflow and water balance
Continuous runoff modeling with daily temporal resolution was carried
out for the Suntar River Basin for the period 1957-1964, using input
meteorological data from four meteorological stations (Suntar-Khayata,
Nizhnyaya Baza, Vostochnaya and Agayakan); and for the period 1966-2012
using the data from two stations (Vostochnaya and Agayakan). The
distribution of water balance components for these periods are presented
in Table 5, and the comparison of observed and calculated streamflow
hydrographs are in Fig. 5 and Fig. 6.
Calculated mean annual precipitation for the Suntar river basin is 344
mm for the 1957-1964 period. Estimated streamflow is 199 mm, which is
10% higher than the observed value (180 mm). Estimated ET averaged
across the whole basin equaled 143 mm.
Maximum precipitation and streamflow annual values for the entire
simulation period reached 486 and 348 mm in 1959, while minimum values
were 259 mm in 1958 and 136 mm in 1963 for the Suntar River basin. The
coefficient of variation of annual streamflow is 0.30.
Here we compare the water balance distribution with data from the other
research basin in the region, the KWBS station, the Kontakovy creek
watershed (area 21.3 km2, average altitude 1070 m).
The value of ET for the KWBS is assessed to be within the range 114 to
137 mm (Lebedeva et al., 2017; Zhuravin, 2004). Mean annual
precipitation and streamflow reached 420 and 280 mm for the period
1948–1997.
The average and median Nash-Sutcliffe efficiency (NS) for the Suntar
River amounted to 0.75 in 1957-1964. The same value for the period of
1966-2012 is lower (average 0.58, median 0.67 with maximum and minimum
values of 0.88 and -0.90, respectively). We attribute this decrease of
efficiency to the lack of meteorological data in the second period, with
two stations being unavailable. Overall, despite some overestimation of
streamflow, the calculated streamflow hydrographs match the observed
ones quite satisfactorily, both in shape and absolute discharge values.
Overestimation of simulated streamflow during the spring freshet may be
associated with the spread of underchannel taliks. In spring, dry
alluvial deposits in the river channels are filled with snowmelt water
and delay the start of freshet and decrease its magnitude (Grave et al.,
1964). Such phenomena are also described by Mikhaylov (2013).
We also compared simulated and observed maximum discharges. The maximum
simulated and observed discharges were 1200 and 1659 respectively during
1957-1964 and 1905 and 1910 during 1966-2012 for the Suntar River basin
(Table 5).
Based on the simulation results, the contribution of each runoff
formation complex (RFC) into total streamflow of the Suntar River was
evaluated (Table 6, Fig. 7). The goltsy complex that covers only 7% of
the basin provides 20% of the total streamflow, and the runoff ratio
(total runoff/total precipitation) averages 0.91. Tundra is the largest
contributor to the runoff formation at the Suntar river catchment –
49% of the total runoff, with a runoff ratio of 0.74. The total
streamflow from the taiga and sparse forest landscapes, which occupy
56% of the territory, is about 31%. The contribution of the goltsy
landscape increases in dry years and may reach up to 28% (for example,
in 1963 the total annual streamflow was only 130 mm, while the
streamflow from the goltsy complex was simulated as 513 mm).