| Summary: | The pan-Arctic is disproportionately affected by global temperature increases due to climate change. Polar amplification and local climate feedback cycles, cause air temperature to rise around 2.4 times faster in the Arctic. The pan-Arctic covers approximately 26 million km2 of subbasins which contribute freshwater to the Arctic Ocean. Large-scale studies of climate warming impacts on terrestrial systems are rare because gathering observed data is expensive, difficult, and dangerous, and what is available is difficult to compile and lacks consistency. Modeled data are required for comprehensive long-term studies. This study analyses the pre-whitened annual trends of modeled soil temperature, water temperature, and river ice thickness for the historical period (1979-2019) and future projections (2020-2100) across the pan-Arctic domain using the AHYPEv4 model. These terrestrial hydrological components directly impact pan-Arctic ecology, and communities through permafrost thaw, increases in water temperature and decreases in river ice thickness. Analysis is done for the entire pan-Arctic domain, at the continental scale by comparing North America and Eurasia, and at the watershed scale for the 12 largest rivers (by historical volumes). Future climate projections come from the sixth phase of the Coupled Model Intercomparison Project, CMIP6. To capture uncertainty of future climate projections and socioeconomic response, an ensemble of climate models (CanESM5, MIROC6, and MRI-ESM2-0) and future warming scenarios (ssp1-2.6 and ssp5-8.5) capture the extreme ends of future change. This study shows increasing trends for future periods. Soil temperature increases from 0.032°C/year to 0.054°C/year, water temperature increases from 0.014°C/year to 0.031°C/year and losses in maximum ice thickness increase from 0.062 cm/year to 0.111 cm/year. Change point analysis shows that socio-economic pathways which result in lower future warming have mitigating effects on future trends mid-century, but higher warming scenarios yield ...
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