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

Abstract

Analysis of streamflow data was conducted for 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 located completely in the zone of continuous permafrost. The main result is the presence of statistically significant (p <0.05) positive trends in monthly streamflow in the autumn-winter period for most of the gauges. Streamflow increases via break points (post 1981) for 17 of the 22 gauges in September (average trend value for the period of record is 58%, or 9.8 mm), and 15 of 22 in October (61%, or 2.0 mm). In November and December, increases are seen in 9 out of 19 (54%, 0.4 mm) and 6 out of 17 non-freezing rivers (95%, 0.15 mm) respectively. Average annual air temperature increases at all 13 meteorological stations of the region by 1.1-3.1 °С over the course of the period 1966-2015. Despite this, the active layer thickness trends are contradictory: it shows an increase of 45 cm, decrease of 77 cm, and no significant trend at the three stations with available soil temperature data. Precipitation decreases in late winter by up to 15 mm over the period of record. Additionally, about 10 mm of precipitation which used to fall as snow at the beginning of winter now falls as rain. Despite the decrease in winter precipitation, no decrease of streamflow is observed during the spring freshet in May and June in the last 50 years (from 1966); moreover, 5 gauges show an increase of 86% or 12.2 mm in spring flood via an abrupt change in 1987-1993. Changes in spring freshet start date were identified for 10 gauges. The trend value varies from 4 to 10 days earlier in May over the period of record. 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 melting of permafrost, glaciers and, aufeises, or changes in groundwater conditions are likely to contribute to these changes in streamflow, but no direct observation of these changes are available. Overall, these changes are likely to have a significant impact on the ecology of the zone of continuous permafrost. Increasing freshwater fluxes to the Arctic Ocean could also impact the Arctic thermohaline circulation. Hydrometeorological data used in this study is combined in a single archive and available at https://doi.pangaea.de/10.1594/PANGAEA.892775.