Warming temperatures are impacting the hydrometeorological regime of Russian rivers in the zone of continuous permafrost

Abstract

Abstract. Large Arctic river basins experience substantial variability in climatic, landscape, and permafrost conditions. However, the processes behind the observed changes at the scale of these basins are relatively poorly understood. While most studies have been focused on the “Big 6” Arctic rivers – the Ob', Yenisey, Lena, Mackenzie, Yukon, and Kolyma – few or no assessments exist for small and medium-sized river basins, such as the Yana and Indigirka River basins. Here, we provide a detailed analysis of streamflow data from 22 hydrological gauges in the Yana and Indigirka River basins with a period of observation ranging from 35 to 79 years up to 2015. These river basins are fully located in the zone of continuous permafrost. Our analysis reveals statistically significant (p<0.05) positive trends in the monthly streamflow time series during the autumn–winter period for most of the gauges. The streamflow increases in a stepwise pattern (post-1981) for 17 out of 22 gauges in September (average trend value for the period of record is 58 % or 9.8 mm) and 15 out of 22 gauges in October (61 % or 2.0 mm). The positive trends are seen in 9 out of 19 rivers that do not freeze in November (54 %, 0.4 mm) and 6 out of 17 rivers that do not freeze in December (95 %, 0.15 mm). Precipitation is shown to decrease in late winter by up to 15 mm over the observational period. Additionally, about 10 mm of precipitation that used to fall as snow at the beginning of winter now falls as rain. Despite the decrease in winter precipitation, no decrease in streamflow has been observed during the spring freshet in May and June in the last 50 years (from 1966); moreover, five gauges show an increase of 86 % or 12.2 mm in spring floods via an abrupt change in 1987–1993. The changes in spring freshet start date are identified for 10 gauges; the earlier onset in May varies from 4 to 10 d over the observational period. We conclude that warmer temperatures due to climate change are impacting the hydrological regime of these rivers via changes in precipitation type (rain replacing snow). Other factors, such as the melting of permafrost, glaciers, and aufeis or changes in groundwater conditions, are likely to contribute as well; however, no direct observations of these changes are available. The changes in streamflow can have a significant impact on the ecology of the zone of continuous permafrost, while the increasing freshwater fluxes to the Arctic Ocean can impact the Arctic thermohaline circulation.

Understanding hydrological processes at a remote mountainous continuous permafrost watershed in a changing environment

“…Generally, the simulated trends are similar to trends in the observed flow values especially in September, when the difference does not exceed 11%. Most hydrological stations in the Indigirka and Yana River Basin show observed change points in the spring period around 1966 (Makarieva et al, 2019). This is similar to the results here, where the change point in simulated flow occurred in 1965.…”

“…There are several main hypotheses most often discussed in the context of increasing river discharge in the Arctic regions: 1) the transformation of the mechanisms of the underground supply as a result of permafrost degradation (Romanovsky et al, 2010;Walwoord et al, 2012), 2) melting of glaciers (Liljedahl et al, 2017) or 3) an increase in precipitation (Dyurgerov, Carter, 2004). Results of modeling in this work allowed us to confirm the assumption stated in Makarieva et al (2019), associated with the reason for the runoff change being due to the increase in the proportion of liquid precipitation during the autumn transitional months.…”

“…The analysis of observed monthly streamflow data in the Suntar River has shown the presence of statistically significant (p <0.05) positive trends in the May and autumn periods. The values of increasing trends are the following: in May -6.8 mm or 103%, in September -9.9 mm or 49%, in October -3.3 mm or 70% and in November -0.43 mm or 52% (Makarieva et al, 2019). The significant trends in simulated streamflow modelled here occur in May -11.3 mm or 118%, in September -10.2 mm or 38.1%, in October -1.3 mm or 33.3% and in November -0.35 mm or 35.9%.…”

“…According to Makarieva et al (2019), there is a decrease in precipitation in the winter of 8 to 13 mm and the absence of significant change in other seasons. The rise of annual air temperature of +2.0°C led to an increase in the amount of liquid precipitation in September by about 12 mm.…”

“…Many Arctic and particularly mountainous river basins are poorly-studied and lack observational and experimental time series data (Hinzman et al, 2005;Viviroli et al, 2011). Analysis of limited observational data suggests that the Arctic river streamflow is changing (Rawlins et al, 2010;Tananaev et al, 2016;Makarieva et al 2019) but the mechanisms of observed changes are not fully understood.…”