Articles | Volume 19, issue 9
Hydrol. Earth Syst. Sci., 19, 3951–3968, 2015
Hydrol. Earth Syst. Sci., 19, 3951–3968, 2015

Research article 24 Sep 2015

Research article | 24 Sep 2015

Uncertainty in hydrological signatures

I. K. Westerberg1,2 and H. K. McMillan3 I. K. Westerberg and H. K. McMillan
  • 1Department of Civil Engineering, University of Bristol, Queen's Building, University Walk, Clifton, BS8 1TR, UK
  • 2IVL Swedish Environmental Research Institute, P.O. Box 21060, 10031, Stockholm, Sweden
  • 3National Institute of Water and Atmospheric Research, P.O. Box 8602, Christchurch, New Zealand

Abstract. Information about rainfall–runoff processes is essential for hydrological analyses, modelling and water-management applications. A hydrological, or diagnostic, signature quantifies such information from observed data as an index value. Signatures are widely used, e.g. for catchment classification, model calibration and change detection. Uncertainties in the observed data – including measurement inaccuracy and representativeness as well as errors relating to data management – propagate to the signature values and reduce their information content. Subjective choices in the calculation method are a further source of uncertainty.

We review the uncertainties relevant to different signatures based on rainfall and flow data. We propose a generally applicable method to calculate these uncertainties based on Monte Carlo sampling and demonstrate it in two catchments for common signatures including rainfall–runoff thresholds, recession analysis and basic descriptive signatures of flow distribution and dynamics. Our intention is to contribute to awareness and knowledge of signature uncertainty, including typical sources, magnitude and methods for its assessment.

We found that the uncertainties were often large (i.e. typical intervals of ±10–40 % relative uncertainty) and highly variable between signatures. There was greater uncertainty in signatures that use high-frequency responses, small data subsets, or subsets prone to measurement errors. There was lower uncertainty in signatures that use spatial or temporal averages. Some signatures were sensitive to particular uncertainty types such as rating-curve form. We found that signatures can be designed to be robust to some uncertainty sources. Signature uncertainties of the magnitudes we found have the potential to change the conclusions of hydrological and ecohydrological analyses, such as cross-catchment comparisons or inferences about dominant processes.

Short summary
This study investigated the effect of uncertainties in data and calculation methods on hydrological signatures. We present a widely applicable method to evaluate signature uncertainty and show results for two example catchments. The uncertainties were often large (i.e. typical intervals of ±10–40% relative uncertainty) and highly variable between signatures. It is therefore important to consider uncertainty when signatures are used for hydrological and ecohydrological analyses and modelling.