Abstract
Abstract. The flow duration curve (FDC) is a fundamental signature of the hydrological cycle to support water management strategies. Despite many studies on this topic, its estimation in ungauged basins is still a relevant issue as the FDC is controlled by different types of processes at different time-space scales, thus resulting quite sensitive to the specific case study. In this work, a regional spatially-smooth procedure to evaluate the annual FDC in ungauged basins is proposed, based on the estimation of the L-moments (mean, L-CV and L-skewness) through regression models valid for the whole case study area. In this approach, homogeneous regions are no longer required and the L-moments are allowed to continuously vary along the river network, thus providing a final FDC smoothly evolving for different locations on the river. Regressions are based on a set of topographic, climatic, land use and vegetation descriptors at the basin scale. Moreover, the model ensures that the mean annual runoff is preserved at the river confluences, i.e. the sum of annual flows of the upstream reaches is equal to the predicted annual downstream flow. The proposed model is adapted to incorporate different "sub-models" to account for local information within the regional framework, where man-induced alterations are known, as common in non-pristine catchments. In particular, we propose a module to consider the impact of existing/designed water withdrawals on the L-moments of the FDC. The procedure has been applied to a dataset of daily observation of about 120 gauged basins on the upper Po river basin in North-Western Italy.
Highlights
Flow duration curves (FDC) are widely used tools to represent water availability in a river basin and are considered for many water resources planning and management purposes, like concessions for water uses and the planning of new hydropower plants
We develop a regional model for prediction of the flow duration curve (FDC) in ungauged basins, developed and applied in the upper Po river basin
The shift could be due to an inaccurate estimation of the L-moments, it can be caused by the presence of unknown water intakes upstream the gauging station
Summary
Flow duration curves (FDC) are widely used tools to represent water availability in a river basin and are considered for many water resources planning and management purposes, like concessions for water uses and the planning of new hydropower plants. A FDC computed for a single year is called “annual”; if the observations of multiple years are merged together, the FDC is usually referred to as “period-ofrecord” or “total”. The evaluation of the FDC in ungauged basins is still a major issue in hydrological modeling, despite a large body of literature available on this topic, as recently reviewed by Castellarin et al (2013). We develop a regional model for prediction of the FDC in ungauged basins, developed and applied in the upper Po river basin (in North-Western Italy, an area mainly characterized by alpine and piedmont environments). The aim of the work is to provide a regional tool to estimate the mean annual FDC in a generic watershed based on morphometric and climatic descriptors
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