Rainbow color map distorts and misleads research in hydrology – guidance for better visualizations and science communication

Abstract

Abstract. Nowadays color in scientific visualizations is standard and extensively used to group, highlight or delineate different parts of data in visualizations. The rainbow color map (also known as jet color map) is famous for its appealing use of the full visual spectrum with impressive changes in chroma and luminance. Besides attracting attention, science has for decades criticized the rainbow color map for its non-linear and erratic change of hue and luminance along the data variation. The missed uniformity causes a misrepresentation of data values and flaws in science communication. The rainbow color map is scientifically incorrect and hardly decodable for a considerable number of people due to color vision deficiency (CVD) or other vision impairments. Here we aim to raise awareness of how widely used the rainbow color map still is in hydrology. To this end, we perform a paper survey scanning for color issues in around 1000 scientific publications in three different journals including papers published between 2005 and 2020. In this survey, depending on the journal, 16 %–24 % of the publications have a rainbow color map and around the same ratio of papers (18 %–29 %) uses red–green elements often in a way that color is the only possibility to decode the visualized groups of data. Given these shares, there is a 99.6 % chance to pick at least one visual problematic publication in 10 randomly chosen papers from our survey. To overcome the use of the rainbow color maps in science, we propose some tools and techniques focusing on improvement of typical visualization types in hydrological science. We give guidance on how to avoid, improve and trust color in a proper and scientific way. Finally, we outline an approach how the rainbow color map flaws should be communicated across different status groups in science.

GC Insights: Rainbow colour maps remain widely used in the geosciences

“…Despite widespread recognition of the weaknesses of the rainbow colour map, and of the wider issues associated with the use of red-green colour schemes, the results of this study suggest that both continue to be widely used in geoscience publications. The results presented here, in line with Stoelzle and Stein (2021), suggest there was a slight reduction in the use of data visualisations with colour issues in 2020; perhaps as (i) awareness of the issues associated with rainbow colour maps has grown, (ii) more journal reviewers and editors identify colour issues and request changes, and/or (iii) more tools and resources become available to support better decision-making with respect to colour schemes. Despite this, over half of geoscience papers published in 2020 still contain at least one visualisation that was ambiguous or non-CVD friendly, and any improvement from previous years appears to be uneven across different geoscience journals and so, by implication, across different geoscience disciplines.…”

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Rainbow colour maps are known to be problematic yet remain widely used in scientific communication. This study extends work by Stoelzle and Stein (2021) to investigate the extent of their use in geoscience publications. It is found that over half (55%) of all papers surveyed from six geoscience journals from the years 2005, 2010, 2015 and 2020 (n=2,638) contained at least one visualisation that uses rainbow or red-green colour schemes and are therefore potentially misleading and colour inaccessible.

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“…Following the approach of Stoelzle and Stein (2021), papers were classified using a four-way classification:…”

“…those containing ambiguous or non-CVD friendly visualisations. When combined with the 797 papers surveyed by Stoelzle and Stein (2021) from the EGU journal Hydrology and Earth System Sciences (HESS), this produced an overall data set of 2,638 papers spanning a range of geoscience disciplines.…”

“…McNeall, 2018;Zeller and Rogers, 2020). A recent systematic review of around 1,000 scientific publications from three different journals by Stoelzle and Stein (2021) concluded that 16-24% of the publications used a rainbow colour map, with a similar proportion (18-29%) using red-green elements without an alternative way of distinguishing them, meaning that approximately one in every two papers have colour issues. In this study, I adopt a similar approach to Stoelzle and Stein (2021), extending their analysis to other geoscience journals, to investigate the use of rainbow and red-green colour schemes across different geoscience disciplines.…”