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Baseflow is the delayed component of streamflow from subsurface storage and is critical for sustaining ecological flows and ensuring water resource security. Understanding controls on and changes in baseflow, including the seasonality of baseflow, is therefore an important task. Baseflow seasonality has typically been investigated using pre-defined hydrological seasons. Instead, here, we investigate baseflow seasonality using data-led approaches that identify and cluster average annual baseflow hydrographs that exhibit early-, mid-, or late-seasonality. We apply a novel functional data analysis (FDA) approach and examine temporal changes in the timing of seasonal peaks in annual standardised baseflow hydrographs for 671 catchments across Great Britain (GB). We use data from the CAMELS-GB dataset for the period 1976 to 2015 split into two twenty-year time blocks (1976-1995 and 1996-2015). Functional clustering enables groups of catchments with similar distributions between time blocks to be identified. Changes in baseflow seasonality with time are investigated by identifying and characterising catchments that move between functional clusters and time blocks, while analysis of the timing of baseflow peaks provides additional temporal resolution to the early-, mid-, and late-season discretisation generated by the functional clustering. The analysis shows that baseflow seasonality has a spatio-temporally coherent structure across GB and catchment characteristics are a first order control on the form of seasonal baseflow clusters. Changes in climate are inferred to be the first order control on changes in baseflow seasonality between the two time blocks. A change to earlier seasonal baseflow in snowmelt influenced catchments in upland northern GB is associated with systematic warming across the two time blocks, and a move to earlier (later) baseflow seasonality across lowland southern, central and eastern (western, north-western and northern) catchments in GB is associated with earlier (later) seasonality in effective rainfall (defined as precipitation minus potential evapotranspiration). These changes in baseflow seasonality in non-snow-melt influenced catchments are consistent with the proposition that, in temperate environments, climate warming leading to vegetation phenology-mediated changes in evapotranspiration may be modifying the timing of hydrological cycles. [ABSTRACT FROM AUTHOR]

Robust projections of changes in the hydrological cycle in a non-stationary climate rely on trustworthy estimates of the water balance elements. Additional drivers than precipitation and temperature, namely wind, radiation, and humidity are known to have a significant influence on processes such as evaporation, snow accumulation, and snow-melt. A gridded version of the rainfall-runoff HBV model is run at a 1 × 1 km scale for mainland Norway for the period 1980–2014, with the following alterations: (i) the implementation of a physically based evaporation scheme; (ii) a net radiation-restricted degree-day factor for snow-melt, and (iii) a diagnostic precipitation phase threshold based on temperature and humidity. The combination of improved forcing data and model alterations allowed for a regional calibration with fewer calibrated parameters. Concurrently, modeled discharge showed equally good or better validation results than previous gridded model versions constructed for the same domain; and discharge trend patterns, snow water equivalent, and potential evaporation compared fairly to observations. Compared with previous studies, lower precipitation and evaporation values for mainland Norway were found. The results suggest that a more robust and more physically based model for climate change studies has been obtained, although additional studies will be needed to further constrain evaporation estimates. HIGHLIGHTS The distributed HBV model is updated with physically based parameterizations.; High-quality forcing data are included to enhance estimates evaporation, precipitation phase, and snow-melt.; More than 100 discharge measurements are used for calibration and validation.; The updates help constrain the long-term water balance for Norway.; Additional work is called for to better constrain the evaporation estimates.;

In late spring of 1992, Christopher McCandless crossed the Teklanika River, west of Healy, Alaska (United States). His summer has been well documented both in the book and the movie ‘Into the Wild.’ In early summer of 1992, he attempted to cross back over the river, but was stopped by high waters and he died later that summer. This paper investigates the hydrologic conditions of the Teklanika River watershed. We consider both climatological conditions and also conditions during the summer of 1992. We run process-based snowpack and runoff models in order to estimate the river hydrograph at the point of Mr. McCandless’ attempted crossing. Our results demonstrate that the Teklanika river is very flashy during the summer, responding rapidly to strong episodic rainfall events. The main snowmelt signal occurred in mid-to-late May, after Mr. McCandless’ first crossing and before his second attempt. The specific day of his attempted re-crossing corresponded to a large runoff event, driven by rainfall. We conclude that Mr. McCandless had unfortunate timing and that, had he tried to cross a day or two earlier or later, the outcome may have been different. This paper is also an opportunity to explore the hydrologic compromises that must be made when trying to study ungauged, or poorly gauged, areas. There is a spectrum of choices regarding input datasets and methodological simplifications and the correct location on that spectrum will depend on the particular watershed the objectives and expectations of the study.

Robust projections of changes in the hydrological cycle in a non-stationary climate rely on trustworthy estimates of the water balance elements. Additional drivers than precipitation and temperature, namely wind, radiation, and humidity are known to have a significant influence on processes such as evaporation, snow accumulation, and snow-melt. A gridded version of the rainfallrunoff HBV model is run at a 1 × 1 km scale for mainland Norway for the period 1980-2014, with the following alterations: (i) the implementation of a physically based evaporation scheme; (ii) a net radiation-restricted degree-day factor for snow-melt, and (iii) a diagnostic precipitation phase threshold based on temperature and humidity. The combination of improved forcing data and model alterations allowed for a regional calibration with fewer calibrated parameters. Concurrently, modeled discharge showed equally good or better validation results than previous gridded model versions constructed for the same domain; and discharge trend patterns, snow water equivalent, and potential evaporation compared fairly to observations. Compared with previous studies, lower precipitation and evaporation values for mainland Norway were found. The results suggest that a more robust and more physically based model for climate change studies has been obtained, although additional studies will be needed to further constrain evaporation estimates. [ABSTRACT FROM AUTHOR]

This study investigates the dynamics of riverine DOC concentrations during a series of stream discharge events (3–10 days) following rainstorms of different intensity and duration. We examined six events, when high-frequency (hourly) water samples for DOC (n = 321) were collected in spring (n = 166) and autumn (n = 155). Results identified three distinct water-mediated processes during stream discharges events that linked DOC source supply from agricultural land surfaces with sinks in a receiving river. These were as follows: 1) snowpack drives significant high DOC concentrations in base-flow during spring, 2) abundant organic matter in topsoil from crop residues determines a rapid DOC loading profile in the first flush, and 3) very large hydro-climatic events in snow-melting season over agricultural watersheds could increase the riverine DOC flux by 2.3 folds. These results revealed that ca. 76.5% of annual DOC was exported during a handful of storm-discharge events (78.9% for spring and 74.2% from autumn) over agricultural landscapes. Given the significant amount of riverine DOC exported from agricultural landscapes during severe weather events, our results suggest that changes in climate promote larger precipitation events that would likely enhance the export of terrestrial DOC to receiving water bodies. The study presents a semi-analytical model that is able to extrapolate the riverine DOC dynamics during storm discharge events of varying duration and intensity (R 2 up to 0.9). [ABSTRACT FROM AUTHOR]

Abstract: Understanding the generation mechanisms of lahars is important for improving volcanic hazard assessments. The Taisho lahar (TL) was generated during the 1926 eruption of Tokachidake Volcano, Japan, and was considered a typical snowmelt lahar caused by the runout of hot debris onto a snow-covered slope. A similar mechanism produced a huge mud flow during the 1985 eruption of Nevado del Ruiz, Colombia. However, the origin of water in such lahars remains a controversial topic because the calculated water mass is based on the assumption that all of the snow on the runout area of the TL was melted, although this is much less than the estimated water volume in the TL estimated by previous studies. I have re-examined proximal deposits of the TL and their paleomagnetic characteristics in order to better understand the eruption sequence and formation of the TL. The TL produced two debris avalanche deposits and a surge-like deposit that had relatively high emplacement temperature (~350°C). The deposits are composed of hydrothermally altered andesitic gravel, sand and mud. The high clay content (3–5wt.% clay in the <2mm fraction) and sedimentary characteristics indicate that the flow was a cohesive lahar, most likely induced by collapse of a hydrothermally altered pyroclastic cone (hypocenter). The presence of the surge deposit indicates that the TL was not caused by simple collapse of a cinder cone but by a phreatic explosion that resulted in sector collapse. This suggests that the hydrothermal system was related to the 1926 eruption. The present-day volcano has a large hydrothermal system (1×106 m3 water) beneath the active crater. This study indicates that hydrothermal system explosions can trigger cohesive lahars that contain both snow melt and hydrothermal pore water, and this indicates the need to monitor hydrothermal systems. [Copyright &y& Elsevier]

This study describes time series analysis of snow-melt, radiation data and energy balance for a seasonal snow cover at Dhundi field station of SASE, which lies in Pir Panjal range of the N-W Himalaya, for a winter season from 13 January to 12 April 2005. The analysis shows that mean snow surface temperature remains very close to the melting temperature of snow. It was found close to −1°C for the complete observational period which makes the snow pack at Dhundi moist from its beginning. The average air temperature over this period was found to be 3.5°C with hourly average variation from −5.5°C to 13°C. The snow surface at this station received a mean short wave radiation of 430W m−2, out of which 298W m−2 was reflected back by the snow surface with mean albedo value of 0.70. The high average temperature and more absorption of solar radiation resulted in higher thermal state of the snowpack which was further responsible for faster and higher densification of the snowpack. Net radiation energy was the major component of surface energy budget with a mean value of 83W m−2. Bulk transfer model was used to calculate turbulent fluxes. The net energy was utilized for satisfying cold content and snow-melt by using measured snow surface temperature and density of snow pack. The mean square error between calculated and measured daily snow-melt was found to be approximately 6.6mm of water equivalent. [ABSTRACT FROM AUTHOR]

Abstract: Both Δ14C and δ13C were used to study transport behavior of particulate organic matter (POM) in the Ishikari River in Japan. Water samples were collected once a month from April to September in 2004. Positive correlations were found between Δ14C and particulate organic carbon (POC) content and Δ14C and δ13C values for the POM samples from June to September. However during snow-melt, distinctive minimum values were found for POC content, Δ14C and δ13C. These results indicate the POC was supplied from different sources and by different mechanisms during spring snow-melt and summer because of variations in water level and discharge. [Copyright &y& Elsevier]

Australian alpine ecosystems are expected to diminish in extent as global warming intensifies. Alpine vegetation patterns are influenced by the duration of snow cover including the presence of snowdrifts in summer, but there is little quantitative information on landscape-scale relationships between vegetation patterns and the frequency of occurrence of persistent summer snowdrifts in the Australian alps. We mapped annual changes in summer snowdrifts in the Kosciuszko alpine region, Australia, from Landsat TM images and modelled the frequency of occurrence of persistent summer snowdrifts from long-term records (1954–2003) of winter snow depth. We then compared vegetation composition and structure among four classes that differed in the frequency of occurrence of persistent summer snowdrifts. We found a curvilinear relationship between annual winter snow depth and the area occupied by persistent snowdrifts in the following summer ( r2 = 0.9756). Only 21 ha (0.42% of study area) was predicted to have supported summer snowdrifts in 80% of the past 50 years, while 440 ha supported persistent summer snow in 10% of years. Mean cover and species richness of vascular plants declined significantly, and species composition varied significantly, as the frequency of summer snow persistence increased. Cushion plants and rushes were most abundant where summer snowdrifts occurred most frequently, and shrubs, grasses and sedges were most abundant in areas that did not support snowdrifts in summer. The results demonstrate strong regional relationships between vegetation composition and structure and the frequency of occurrence of persistent summer snowdrifts. Reductions in winter snow depth due to global warming are expected to lead to substantial reductions in the extent of persistent summer snowdrifts. As a consequence, shrubs, grasses and sedges are predicted to expand at the expense of cushion plants and rushes, reducing landscape vegetation diversity. Fortunately, few vascular plant species (e.g. Ranunculus niphophilus) appear to be totally restricted to areas where summer snow occurs most frequently. The results from this study highlight potential indicator species that could be monitored to assess the effects of global warming on Australian alpine environments. [ABSTRACT FROM AUTHOR]

Snow-covered area (SCA) is a critical input in snow-melt run-off studies. It is difficult to get timely information about SCA, especially of mountain watersheds, by conventional survey methods, including aerial surveys. With the advent of satellite remote sensing, it has now become possible to obtain reliable and regular SCA data. This has led to the development of snow-melt run-off simulation and forecasting models using SCA derived from LANDSAT and NOAA data; the models in use in USA and India are described. [ABSTRACT FROM AUTHOR]