8. Simulated streamflow trends
Studying the mechanisms of runoff regime transformation changes in the
Arctic basins in current and future climate conditions is important
research task. In general, river streamflow in Northern Eurasia and
North America is increasing (Shiklomanov & Lammers, 2013). Most of the
rivers exhibit the increase of winter base flow (Makarieva et al. 2019a;
Spence et al., 2011; Tananaev et al., 2016) and there are different
hypothesis about the factors of such changes. The analysis of monthly
streamflow data in the basins of the Yana and Indigirka Rivers
(1936-2015) has shown the presence of statistically significant (p
<0.05) positive trends in May and autumn period (Makarieva et
al., 2019a). The values of trends for the Suntar River are the
following: 6.8 mm or 103 % in May, 9.9 mm or 49 % in September, 3.3 mm
or 70% in October and 0.43 mm or 52% in November (Makarieva et al.,
2019a). There is a decrease in precipitation in winter (minus 8 to 13
mm) and the absence of significant changes in other seasons. The rise of
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 changes of these hydrometeorological
characteristics are simultaneously observed, indicate that the phase
state of precipitation can be among main factors affecting the increase
of low flows of studied rivers.
According the Mann-Kendall and Spearman rank-correlation tests (Kendall,
1975; Mann, 1945) and Pettitt’s test (Pettitt, 1979) significant
positive trends of simulated streamflow was in May (1.3 mm or 118 %),
September (10.2 mm or 38.1%), in October (1.3 mm or 33.3%) and
November (0.35 mm or 35.9%) (Nesterova et al., 2019). Thus, the
simulated trends do coincide with the observed trends of stream flow
values (Table 7). The share of liquid precipitation increased by an
average of 10 % or 13.6 mm, which corresponds to the observed value of
12 mm. The change point in the autumn season coincides with the observed
data and refers to the period 1993-1996 (Fig. 8).