The “dirty dozen” of freshwater science: Detecting then reconciling hydrological data biases and errors
journal contributionposted on 17.03.2017 by Robert Wilby, Nicholas Clifford, Paolo De Luca, Shaun Harrigan, John Hillier, Richard Hodgkins, Matthew F. Johnson, Tom K.R. Matthews, Conor Murphy, Simon Noone, Simon Parry, Christel Prudhomme, Stephen Rice, Louise Slater, Katie Smith, Paul Wood
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Sound water policy and management rests on sound hydrometeorological and ecological data. Conversely, unrepresentative, poorly collected or erroneously archived data introduces uncertainty regarding the magnitude, rate and direction of environmental change, in addition to undermining confidence in decision-making processes. Unfortunately, data biases and errors can enter the information flow at various stages, starting with site selection, instrumentation, sampling/ measurement procedures, post-processing and ending with archiving systems. Techniques such as visual inspection of raw data, graphical representation and comparison between sites, outlier and trend detection, and referral to metadata can all help uncover spurious data. Tell-tale signs of ambiguous and/or anomalous data are highlighted using 12 carefully chosen cases drawn mainly from hydrology (‘the dirty dozen’). These include evidence of changes in site or local conditions (due to land management, river regulation or urbanisation); modifications to instrumentation or inconsistent observer behaviour; mismatched or misrepresentative sampling in space and time; treatment of missing values, post-processing and data storage errors. As well as raising awareness of pitfalls, recommendations are provided for uncovering lapses in data quality after the information has been gathered. It is noted that error detection and attribution are more problematic for very large data sets, where observation networks are automated, or when various information sources have been combined. In these cases, more holistic indicators of data integrity are needed that reflect the overall information life-cycle and application(s) of the hydrological data.
This paper was inspired by a capacity building program supported by the European Bank for Reconstruction and Development. Data for Exhibits #3, #5 and #12 are freely available from the UK NRFA. Other public data sources are acknowledged in Figure legends. Authors CP, KS, SH and SP are supported by the NERC-CEH Water Resources Science Area
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