Recent Changes to the Hydrological Cycle of an Arctic basin at the Tundra-Taiga Transition
Abstract. The impact of observed changes in climate and vegetation on the hydrology of Arctic basins is often considered to be most sensitive at the tundra-taiga transition where the region is warmest and sub-arctic vegetation is nearest. This study uses weather and land cover observations and a cold regions hydrological model to investigate historical changes in modelled hydrological processes driving the streamflow response of a small Arctic permafrost-underlain basin at the tundra-taiga transition. The physical processes found in this environment and explicit changes in vegetation type and density were simulated and validated against observations of streamflow discharge, snow water equivalent and active layer thickness. Mean air temperature and all-wave irradiance have increased by 3.7 °C and 8.4 W m−2, respectively, while precipitation has decreased from 369 to 321 mm since 1960. Two modelling scenarios were created to separate the effects of changing climate and vegetation on hydrological processes. Results show that over 1960–2016 most hydrological changes were driven by climate changes, such as decreasing snowfall by 7.8 mm decade−1, deepening active layer thickness by 1.8–4.2 cm decade−1, earlier snowcover depletion and ground thaw initiation dates from 1.5 to 3 and by 1 to 3 days decade−1, respectively, and diminishing annual sublimation and soil moisture by 1.3 and 5.9 mm decade−1, respectively. Evapotranspiration decreased by 2.5 mm decade−1, due to decreasing irradiance and soil moisture. Shrub expansion and densification decreases blowing snow redistribution by 20 to 40 mm and sublimation by 1 to 10 mm. Streamflow dropped by 40 mm as a response to the 48 mm decrease in precipitation, suggesting a small degree of hydrological resiliency. These results represent the first detailed estimate of hydrological changes occurring in small Arctic basins, and can be used as a reference to inform other studies of Arctic climate change impacts.