Resolving the climate-controlled hydrological regime in a model permafrost catchment for future management strategies.

Climate change influences worldwide freshwaters with the most prominent effects in the Arctic and Alpine regions. Environmental management in proglacial zones underlain by permafrost requires understanding of hydrological regimes and water retention patterns. However, there is limited long-term data on the catchment-scale freshwater flow and retention for ecosystems within the continuous permafrost zones. Here, we characterized the hydrometeorological controls on the glacial-fluvio-lacustrine regime in a model Arctic catchment (SW Svalbard) to inform contingency plans for regions endangered by glacial-floods and permafrost landslides. We compiled a comprehensive hydro-meteorological dataset between 2005 and 2019 from a larger database (1972-2019) and applied bootstrapping, random forest, and multiple regressions, to elucidate the relationships between drivers (temperatures, sunshine duration, precipitation) and the intensity of freshwater flows. The hydrology exhibits strong seasonality with a pronounced peak between June and July controlled by precipitation (R = 0.56). From August to September, low-to-intermediate freshwater discharge is controlled by interactive effects of air temperatures and precipitation (R = 0.71). The interaction between hydrometeorology and catchment-scale discharge is stronger for August and September compared to June and July. The strongest warming trend between August and September (1979-2019) makes this period particularly relevant with regards to the long-term changes and environmental management in the permafrost-underlain catchments. Indeed, our northern hemisphere meta-analysis (n = 1975) revealed that majority of glacial floods (51 %) occurs at that time. We argue that permafrost management should include monitoring of surface temperature, precipitation and snow cover enabling establishment of stabilizing infrastructure in sensitive regions whenever threshold values are exceeded (i.e., Tmin >4 °C; P > 30 mm) and discharges increase.