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.
Highlights
In terms of correct encoding, visual mappings such as position, length, angle, direction, area and volume rank higher in efficiency and accuracy than color (e.g., Wong, 2010)
In this study we evaluate the use of rainbow and red– green color use in the journal Hydrology and Earth System Sciences (HESS) in preprints and publications in 2020 and their use over time (2005–2020)
We extended the survey for all papers published in HESS in 2015, 2010 and 2005 to better understand if there is or was a tendency towards more or fewer rainbow-colored visualizations in scientific publications (Fig. 2, Table A1; https://github.com/modche/rainbow_hydrology, last access: 23 August 2021)
Summary
Colorful visualizations are deeply integrated in science communication. In hydrology, visualization of water fluxes like precipitation, evapotranspiration, discharge or percolation and terms like green and blue water, humidity and aridity, or flood and drought are subjects of the daily hydrologists work. The rainbow color map attracts attention but is weak in representing data in a scientifically correct way (Fig. 1) This affects all people, even those with normal color vision. A thoughtful and scientifically correct color map should allow for all types of dichromatic views (i.e., color vision deficiency) and unambiguous perception of the displayed data. As it is scientific standard and best practice to avoid any rainbow or rainbow-derivate color map (Crameri et al, 2020), we want to challenge the use of rainbow color maps in hydrological science by analyzing the status quo of rainbow visualizations in hydrological and environmental publications. We discuss alternatives for using color overall in scientific publications and how to improve and trust the use of color
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