Abstract Hydrological signatures that represent snow processes are valuable to gain insights into snow accumulation and snow melt dynamics. We investigated five snow signatures. Considering inter‐annual average of each calendar day, two slopes derived from the relation between streamflow and air temperature for different periods and streamflow peak maxima are used as signatures. In addition, two different approaches are used to compute inter‐annual average and yearly snow storage estimates. We evaluated the ability of these signatures to characterize average (a) snow melt dynamics and (b) snow storage. They were applied in 10 Critical Zone Observatory catchments of the Southern Sierra mountains (USA) characterized by a Mediterranean climate. The relevance and information content of the signatures are evaluated using snow depth and snow water equivalent measurements as well as inter‐catchment differences in elevation. The slopes quantifying the relations between streamflow and air temperature and the date of streamflow peak were found to characterize snow melt dynamics in terms of snow melt rates and snow melt affected areas. Streamflow peak dates were linked to the period of highest snow melt rates. Snow storage could be estimated both on average, considering all years, and for each year. Snow accumulation dynamics could not be characterized due to the lack of streamflow response during the snow accumulation period. The signatures were found potentially valuable to gain insights into catchment scale snow processes. In particular, when comparing catchments or observed and simulated data, they could provide insights into differences in terms of (a) snow melt rate and/or snow melt affected area over the snow melt season and (b) average or yearly snow storage. Requiring only widely available data, these hydrological signatures can be valuable for snow processes characterization, catchment comparison/classification or model development, calibration or evaluation.
Abstract Streamflow data measured at hydrometric stations are affected by uncertainty due to water level (or stage) measurement errors. This uncertainty increases as the sensitivity of the stage‐discharge controls decreases. A recently proposed method is used to demonstrate the role of control sensitivity in propagating stage uncertainty to streamflow uncertainty among other error sources. The method is first applied to a fictitious hydrometric station with five alternative scenarios of controls with variable sensitivity. The fictitious controls are designed on a flat weir without or with triangular or rectangular notches. The method is also evaluated using a real hydrometric station where the initially flat weir was changed to a weir with a rectangular notch. Both applications confirm the importance of the sensitivity of the controls, showing that a narrow notch in a flat control substantially reduces the uncertainty of daily, monthly and yearly discharges as well as the uncertainty of a low flow index. Quantifying such uncertainty component is essential to optimize the design of hydrometric stations and to provide streamflow data with acceptable uncertainty, especially for low flows.
Abstract. This study explores how catchment heterogeneity and variability can be summarized in simplified models, representing the dominant hydrological processes. It focuses on Mediterranean catchments, characterized by heterogeneous geology, pedology and land use, as well as steep topography and a rainfall regime in which summer droughts contrast with high-rainfall periods in autumn. The Ardèche catchment (Southeast France), typical of this environment, is chosen to explore the following questions: (1) can such a Mediterranean catchment be adequately characterized by a simple dynamical systems approach and what are the limits of the method under such conditions? (2) what information about dominant predictors of hydrological variability can be retrieved from this analysis in such catchments? In this work we apply the data-driven approach of Kirchner (2009) to estimate discharge sensitivity functions that summarize the behaviour of four sub-catchments of the Ardèche, using low-vegetation periods (November–March) from 9 years of measurements (2000–2008) from operational networks. The relevance of the inferred sensitivity function is assessed through hydrograph simulations, and through estimating precipitation rates from discharge fluctuations. We find that the discharge sensitivity function is downward-curving in double-logarithmic space, thus allowing further simulation of discharge and non-divergence of the model, only during low-vegetation periods. The analysis is complemented by a Monte Carlo sensitivity analysis showing how the parameters summarizing the discharge sensitivity function impact the simulated hydrographs. The resulting discharge simulation results are good for granite catchments, which are likely to be characterized by shallow subsurface flow at the interface between soil and bedrock. The simple dynamical system hypothesis works especially well in wet conditions (peaks and recessions are well modelled). On the other hand, poor model performance is associated with summer and dry periods when evapotranspiration is high and low-flow discharge observations are inaccurate. In the Ardèche catchment, inferred precipitation rates agree well in timing and amount with observed gauging stations and SAFRAN climatic data reanalysis during the low-vegetation periods. The model should further be improved to include a more accurate representation of actual evapotranspiration, but provides a satisfying summary of the catchment functioning during wet and winter periods.
Abstract. The presence of a ski resort modifies the snow cover at the local scale, due to snow management practices on ski slopes, especially grooming and snowmaking, which affect the quantity and physical behavior of the snowpack. Snow management exerts two-fold disturbances to the local hydrological cycle, through (i) uptake of water used for snowmaking, either directly after uptake or following temporary storage and (ii) changes in water runoff due to added snow mass through snowmaking and/or delayed melting of the snowpack due to snow grooming. This induces a local pressure on water resources that can be substantial in places and fuels controversies regarding the environmental impact of ski resorts. However, no scientific study to date has quantified the quantitative and qualitative disruption of the local hydrological cycle downstream, concerning both the modification of the local seasonality of the flows (e.g. low water periods) and possible modifications of the volume of water returned. Here we describe results from a case study quantifying the various components of the water budget of a small catchment (several km2), partly covered by a ski resort, in the Northern French Alps. Snow cover simulations, including the timing and amount of snowmelt, were performed using the Crocus snow cover model driven by the SAFRAN reanalysis and future climate scenarios, with and without accounting for grooming and snowmaking. Our study demonstrates a visible impact of snow grooming, through the quasi-suppression of winter snowmelt, leading to delayed snowmelt onset. Snowmaking leads to additional snowmelt amount, of the order of a few percent at the scale of the catchment, scaling with the fraction of the catchment covered by ski pistes, and the fraction of the ski pistes equipped with snowmaking. Under the situation of the case studied, there is no substantial further water loss due to snowmaking after the snow production itself, which induces about 10 % of evaporative loss of water used for snowmaking, related to the snow production process. Snowmaking mainly leads to a moderate shift in snow cover formation and snowmelt processes, to a smaller degree than the influence of future climate change on mountain hydrology. This study provides quantitative estimates of the impact of grooming and snowmaking on the hydrological regime of mountain catchments interesected by ski resorts, which can inform further studies addressing water management and climate change adaptation in mountain regions harbouring ski tourism infrastructure.
