Runoff regime estimation at high-elevation sites: a parsimonious water balance approach

E Bartolini,P Claps,P Allamano,F Laio

doi:10.5194/hess-15-1661-2011

E Bartolini, P Claps + Show 2 more

Open Access

https://doi.org/10.5194/hess-15-1661-2011

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Abstract

Abstract. We develop a water balance model, parsimonious both in terms of parameterization and of required input data, to characterize the average runoff regime of high-elevation and scarcely monitored basins. The model uses a temperature threshold to partition precipitation into rainfall and snowfall, and to estimate evapotranspiration volumes. The role of snow in the transformation of precipitation into runoff is investigated at the monthly time scale through a specific snowmelt module that estimates melted quantities by a non-linear function of temperature. A probabilistic representation of temperature is also introduced, in order to mimic its sub-monthly variability. To account for the commonly reported rainfall underestimation at high elevations, a two-step precipitation adjustment procedure is implemented to guarantee the closure of the water balance. The model is applied to a group of catchments in the North-Western Italian Alps, and its performances are assessed by comparing measured and simulated runoff regimes both in terms of total bias and anomalies, by means of a new metric, specifically conceived to compare the shape of the two curves. The obtained results indicates that the model is able to predict the observed runoff seasonality satisfactorily, notwithstanding its parsimony (the model has only two parameters to be estimated). In particular, when the parameter calibration is performed separately for each basin, the model proves to be able to reproduce the runoff seasonality. At the regional scale (i.e., with uniform parameters for the whole region), the performance is less positive, but the model is still able to discern among different mechanisms of runoff formation that depend on the role of the snow storage. Because of its parsimony and the robustness in the approach, the model is suitable for application in ungauged basins and for large scale investigations of the role of climatic variables on water availability and runoff timing in mountainous regions.

Highlights

Runoff regime, intended as the sequence of mean monthly runoff values, is a useful indicator of the seasonality of runoff, to be used for the development of water management strategies
We examine the presence of dams and flow regulation infrastructures, that may affect the regime shape by reducing the discharge variability. To this aim we introduce a reservoir index, RI = Vl/Vw, defined as the ratio between the sum of the total retention volumes of the artificial lakes located within the basin, Vl, and the average water volume that flows at the basin outlet in a year, Vw
The effectiveness of the reconstructed runoff regime is quantified by a quality index QI

Summary

Introduction

Runoff regime, intended as the sequence of mean monthly runoff values, is a useful indicator of the seasonality of runoff, to be used for the development of water management strategies. A reliable estimation of runoff regime is important in mountainous regions, as these areas supply fresh water in their close neighborhoods and in the lowlands downstream, where most of the economic and agricultural activities take place. Thanks to their ease of use and flexibility, these models are suitable for applications at different spatial scales (Gleick, 1986), and they have been extensively used for climate change impact assessment studies in various catchments all over the world (e.g., Xu et al, 1996; Jasper et al, 2004; Wang et al, 2009)

Results

Discussion

Conclusion