ALBERT

Beschreibung: Nine mid- to high-latitude headwater catchments —part of the North-Watch (Northern Watershed Ecosystem Response to Climate Change) program — were used to analyze threshold response to rainfall and snowmelt-driven events, and link the different responses to the catchment characteristics of the nine sites. The North-Watch data include daily time-series of various lengths of multiple variables such as air temperature, precipitation and discharge. Rainfall and meltwater inputs were differentiated using a degree-day snowmelt approach. Distinct hydrological events were identified, and precipitation-runoff response curves were visually assessed. Results showed that eight of nine catchments showed runoff initiation thresholds and effective precipitation input thresholds. For rainfall-triggered events, catchment hydroclimatic and physical characteristics (e.g., mean annual air temperature, median flow path distance to the stream, median sub-catchment area) were strong predictors of threshold strength. For snowmelt-driven events, however, thresholds and their governing factors controlling precipitation-runoff response were difficult to identify. The variability in catchments responses to snowmelt was not fully explained by runoff initiation thresholds and input magnitude thresholds. The quantification of input intensity thresholds (e.g., snow melting and permafrost thawing rates) is likely required for an adequate characterization of nonlinear spring runoff generation in such northern environments. This article is protected by copyright. All rights reserved.

Beschreibung: We combined a conceptual rainfall-runoff model and input-output relationships of stable isotopes to understand ecohydrological influences on hydrological partitioning in snow-influenced northern catchments. Six sites in Sweden (Krycklan), Canada (Wolf Creek; Baker Creek; Dorset), Scotland (Girnock) and the USA (Dry Creek) span moisture and energy gradients found at high-latitudes. A meta-analysis was carried out using the HBV-model to estimate the main storage changes characterising annual water balances. Annual snowpack storage importance was ranked as Wolf Creek 〉 Krycklan 〉 Dorset 〉 Baker Creek 〉 Dry Creek 〉 Girnock. The subsequent rate and longevity of melt was reflected in calibrated parameters that determine partitioning of waters between more rapid and slower flowpaths and associated variations in soil and groundwater storage. Variability of stream water isotopic composition depends on: (i) rate and duration of spring snowmelt; (ii) significance of summer/autumn rainfall; (iii) relative importance of near-surface and deeper flowpaths in routing water to the stream. Flowpath partitioning also regulates influences of summer evaporation on drainage waters. Deviations of isotope data from the Global Meteoric Water Line showed subtle effects of internal catchment processes on isotopic fractionation most likely through evaporation. Such effects are highly variable among sites and with seasonal differences at some sites. After accounting for climate, evaporative fractionation is strongest at sites where lakes and near-surface runoff processes in wet riparian soils can mobilize isotopically-enriched water during summer and autumn. Given close soil-vegetation coupling, this may result in spatial variability in soil water isotope pools available for plant uptake. We argue that stable isotope studies are crucial in addressing the many open questions on hydrological functioning of northern environments. This article is protected by copyright. All rights reserved.

Beschreibung: There is no scientific consensus about how dissolved organic carbon (DOC) in surface waters is regulated. Here we combine recent literature data from 49 catchments with detailed stream and catchment process information from nine well established research catchments at mid- to high latitudes to examine the question of how climate controls stream water DOC. We show for the first time that mean annual temperature (MAT) in the range from −3° to +10° C has a strong control over the regional stream water DOC concentration in catchments, with highest concentrations in areas ranging between 0° and +3° C MAT. Although relatively large deviations from this model occur for individual streams, catchment topography appears to explain much of this divergence. These findings suggest that the long-term trajectory of stream water DOC response to climate change may be more predictable than previously thought.

Beschreibung: We examine how tracer studies have enhanced our understanding of flow paths, residence times and sources of stream flow in northern catchments. We define northern catchments as non-glacial sites in the temperate conifer/boreal/permafrost zone, focussing our review mainly on sites in North America and Europe. Improved empirical and theoretical understanding of hydrological functioning has advanced the analytical tools available for tracer-based hydrograph separations, derivation of transit time distributions and tracer-aided rainfall-runoff models that are better able to link hydrological response to storage changes. However, the lack of comprehensive tracer data sets still hinders development of a generalized understanding of how northern catchments will respond to change. This paucity of empirical data leads to many outstanding research needs, particularly in rapidly changing areas that are already responding to climatic warming and economic development. To continually improve our understanding of hydrological processes in these regions our knowledge needs to be advanced using a range of techniques and approaches. Recent technological developments for improved monitoring, distributed hydrological sensor systems, more economic analysis of large sample numbers in conjunction with novel, tracer-aided modelling approaches and the use of remote sensing have the potential to help understanding of northern hydrological systems as well as inform policy at a time of rapid environmental change. This article is protected by copyright. All rights reserved.

Beschreibung: Urban sprawl and regional climate variability are major stresses on surface water resources in many places. The Lake Simcoe watershed (LSW) Ontario, Canada, is no exception. The LSW is predominantly agricultural but is experiencing rapid population growth due to its proximity to the greater Toronto area. This has led to extensive land use changes which have impacted its water resources and altered runoff patterns in some rivers draining to the lake. Here, we use a paired-catchment approach, hydrological change detection modelling and remote sensing analysis of satellite images to evaluate the impacts of land use change on the hydrology of the LSW (1994 to 2008). Results show that urbanization increased up to 16% in Lovers Creek, the most-urban impacted catchment. Annual runoff from Lovers Creek increased from 239 to 442 mm/yr in contrast to the reference catchment (Black River at Washago) where runoff was relatively stable with an annual mean of 474 mm/yr. Increased annual runoff from Lovers Creek was not accompanied by an increase in annual precipitation. Discriminant function analysis suggests that early (1992–1997; pre-major development) and late (2004–2009; fully urbanized) periods for Lovers Creek separated mainly based on model parameter sets related to runoff flashiness and evapotranspiration. As a result, parameterization in either period cannot be used interchangeably to produce credible runoff simulations in Lovers Creek due to greater scatter between the parameters in canonical space. Separation of early and late period parameter sets for the reference catchment was based on climate and snowmelt related processes. This suggests that regional climatic variability could be influencing hydrologic change in the reference catchment whereas urbanization amplified the regional natural hydrologic changes in urbanizing catchments of the LSW. This article is protected by copyright. All rights reserved.

Beschreibung: Nature Geoscience 10, 324 (2017). doi:10.1038/ngeo2947 Authors: Hjalmar Laudon, Christopher Spence, Jim Buttle, Sean K. Carey, Jeffrey J. McDonnell, James P. McNamara, Chris Soulsby & Doerthe Tetzlaff

Beschreibung: Nature Geoscience 10, 324 (2017). doi:10.1038/ngeo2947 Authors: Hjalmar Laudon, Christopher Spence, Jim Buttle, Sean K. Carey, Jeffrey J. McDonnell, James P. McNamara, Chris Soulsby & Doerthe Tetzlaff

Beschreibung: There is a growing awareness that mid- to high latitude regions will be strongly affected by climate change. These changes are predicted to be especially pronounced during winter, particularly at higher latitudes. To test how water quality in northern catchments could be affected by warmer winter climates, we assembled long-term data from eight well-studied catchments in Sweden, Scotland, Canada, and the USA across a climatic gradient spanning -2 to +9°C in mean annual temperature and between -11.6 to 6.1°C in average winter temperature. We used the climatic gradient combined with inter-annual variability among catchments to examine how warmer winters could affect the seasonality (seasonal timing) and synchroneity (coupling) of water and dissolved organic carbon (DOC) fluxes. In general, sites with colder winters (〈 -5°C) experienced an export concentrated in spring, whereas sites with warmer winters (〉 0°C) displayed a more evenly distributed export across all seasons. Catchments with warmer winters also displayed less synchroneity between water and DOC flux during winter compared to colder sites, while the opposite was found for the spring. Patterns from the climatic gradient were supported by inter-annual variability at individual sites where both seasonality and synchroneity in the spring were related to the temperature during the preceding winter. Our findings suggest that one likely consequence of warmer winters in northern regions is that the proportion of the annual DOC and water export will increase during winter and decrease during spring and summer. This is of importance as it is the latter seasons during which downstream utilization of both water and DOC often is largest. Copyright © 2012 John Wiley & Sons, Ltd.