River discharge dynamics of major Arctic catchments and their linkage to permafrost thaw
The Arctic is the fastest-warming region on Earth. Enhanced air temperatures are causing rapid environmental changes such as earlier snowmelt or increased permafrost thaw. Because rivers integrate processes occurring throughout catchments, these changes have major implications for how Arctic watersheds store and release water (the so-called “storage-discharge relationship”). Long-term discharge measurements of Arctic rivers show an increasing trend (Figure 1), which is strong evidence for the intensification of the Arctic water cycle.
The main underlying causes of this hydrological change, however, remain elusive. Identifying the controls of Arctic discharge is challenging because various processes are at interplay, including (i) changes in cold-season precipitation, (ii) increased permafrost thaw, (iii) increased evapotranspiration, (iv) changes in vegetation and (v) changes in snow and glacier melt and accumulation.
The activation of groundwater flow systems due to permafrost thaw is suspected to be a key driver of increased discharge, particularly under low-flow conditions. As permafrost thaws, layers of the year-round unfrozen ground are created (so-called taliks; Figure 2). Taliks represent new subsurface pathways enabling groundwater recharge and eventual discharge to streams (Fig. 1, adapted from Walvoord and Kurylyk, 2016). Subsequently, water flow paths are expected to become deeper and longer.
Recent research (Hinzmann et al., 2020) has shown that an increase in non-linearity of the storage-discharge relationship for sub-Arctic catchments is linked to enhanced permafrost thaw. Thus, assessing the linearity of storage-discharge relationships of Arctic catchments can help to identify if thawing permafrost is indeed one of the controlling factors of increasing discharge in the High Arctic.
This hypothesis can be corroborated with the evolution of river water chemistry, which can potentially indicate a trend in longer, deeper flow paths.
The aim of this master’s thesis is (i) to assess long-term trends in storage-discharge relationships of major Arctic rivers and (ii) link this assessment to long-term observations in stream water chemistry.
To this end, the student will
- synthesize a dataset of existing discharge and stream water chemistry data of at least 8 major catchments spread across the Arctic (data available from e.g., https://arcticgreatrivers.org/data/ and https://www.bafg.de/GRDC/EN/04_spcldtbss/41_ARDB/ardb.html)
- perform a recession analysis to quantify storage-discharge relationships (based on the approach of Hinzman et al., 2020)
- perform statistical analysis to test the linkage between changes in storage-discharge relationships and stream water chemistry
- link results from above to changes in permafrost extent (existing maps)
- Hinzman, A. M., Sjöberg, Y., Lyon, S. W., Ploum, S. W., & van der Velde, Y. (2020). Increasing non‐linearity of the storage‐discharge relationship in sub‐Arctic catchments. Hydrological Processes, 34(19), 3894-3909
- Walvoord, M. A., & Kurylyk, B. L. (2016). Hydrologic Impacts of Thawing Permafrost-A Review. Vadose Zone Journal, 15(6), vzj2016.01.0010. doi: 10.2136/vzj2016.01.0010