Sankey Diagrams for Research Papers: Energy, Carbon, Budget and Workflow Examples

Few charts tell a flow story as cleanly as a Sankey diagram. In one picture it shows where something starts, where it ends up, and how much gets lost or transformed along the way. That makes it a natural fit for research papers dealing with energy balance, carbon flow, water budgets, material flow, funding allocation or cohort movement.

The catch is that a lot of Sankey diagrams look impressive but fall apart as scientific figures. The bands aren't proportional, the labels crowd each other, the units vanish, and the reader is left guessing whether they're looking at a loss, a transformation or a category split.

This guide walks through how to design a Sankey diagram that holds up in a paper, and how to get a usable first draft out of the SciDraw AI Sankey Diagram Generator.

A research Sankey diagram should make sources, transformations, losses and final uses obvious at a glance.

Quick Answer: When Should You Use a Sankey Diagram?

Reach for a Sankey diagram when your research needs to show:

• proportional flows between stages,
• input-output balance,
• losses or leakage,
• how a budget or resource gets redistributed,
• the movement of people, samples, energy, carbon, water or material.

Skip it if all you need is to compare independent categories side by side. A bar chart usually does that job better. The Sankey diagram earns its place when the connections between categories are the point.

Common Mistakes in Research Sankey Diagrams

Mistake 1: Band Widths Are Decorative

In a proper Sankey diagram, the width of a band is the quantity. Once those widths are eyeballed or drawn by hand without a scale, the figure starts lying to the reader.

Mistake 2: Units Are Missing

Every flow needs a unit: TWh, kg C, mm/year, dollars, samples, patients or a percentage. "Large" and "small" might pass in a slide deck, but they won't hold up in a paper.

Mistake 3: Too Many Tiny Branches

A Sankey diagram becomes unreadable the moment every small category gets its own band. When the minor ones don't change the scientific interpretation, fold them into an "Other" branch.

Mistake 4: Direction Is Ambiguous

Most research Sankey diagrams read left to right. If yours runs in another direction, say so explicitly with arrows, stage labels or a short caption.

A Practical Sankey Diagram Structure

Before you draw anything, write the flow out as a simple table:

Source	Target	Value	Unit
Total input	Conversion	100	TWh
Conversion	Useful output	62	TWh
Conversion	Losses	38	TWh

Then work through four questions:

1. What is the starting quantity?
2. What are the major intermediate stages?
3. Where does loss or leakage happen?
4. What final outcomes should the reader be comparing?

Example 1: Energy Balance Sankey Diagram

Energy studies usually need to lay out primary energy sources, conversion losses and end-use sectors.

A good structure:

• sources: coal, gas, oil, nuclear, renewables,
• conversion: electricity generation, transport fuel, direct heat,
• end uses: industry, residential, transport, services,
• loss branches: rejected heat, distribution losses.

Prompt for SciDraw AI:

Create a Sankey diagram for a national energy balance. Show coal, gas, oil, nuclear and renewables flowing into conversion, then into electricity, transport, industry and residential use. Add losses as separate branches. Use proportional band widths in TWh and clear labels.

Example 2: Research Grant Budget Sankey Diagram

A grant budget Sankey shows how the total funding is allocated without dragging the reader through a dense table.

Budget Sankey diagrams work well in grant proposals, annual reports and project summaries.

Useful categories:

• personnel,
• equipment,
• consumables,
• travel,
• data services,
• publication fees,
• overhead.

The trick is to keep the diagram honest. If overhead isn't part of the direct research budget, label it as overhead rather than burying it inside a vague "operations" category.

Example 3: Carbon Flow Sankey Diagram

Ecology, climate and environmental science papers often need to trace carbon as it moves through a system.

Carbon flow diagrams should keep fixation, transfer, respiration and decomposition distinct.

A possible flow:

Atmospheric CO2 -> producers -> herbivores -> carnivores
Producers -> respiration
Herbivores -> respiration
Dead biomass -> decomposers -> CO2

For publication, always state whether the values are annual flux, standing stock, model output or measurement.

Example 4: Water Budget Sankey Diagram

Hydrology diagrams typically need to split precipitation into evapotranspiration, runoff, infiltration and recharge.

Prompt:

Create a watershed water budget Sankey diagram. Start with annual precipitation, then split into evapotranspiration, surface runoff, infiltration and groundwater recharge. Use millimetres per year as units and make band widths proportional.

Example 5: Workflow or Cohort Movement

Sankey diagrams aren't limited to physical flows. For a clinical or educational cohort, one can trace how participants move from stage to stage.

Examples:

• enrolled -> screened -> randomized -> completed -> analyzed,
• admitted students -> year 1 -> year 2 -> graduated / transferred / dropped out,
• samples collected -> QC passed -> sequenced -> analyzed -> excluded.

For human-subject studies, don't let the Sankey diagram stand in for a required CONSORT or PRISMA diagram. It can supplement the paper, but formal reporting standards may call for a specific layout.

How to Make a Sankey Diagram with SciDraw AI

Open https://sci-draw.com/sankey-diagram-generator and describe the flow in plain language. You'll get the best results when you include:

• source and target names,
• numeric values,
• units,
• whether losses should be split out,
• the orientation you want,
• the color logic.

Poor prompt:

Make a Sankey diagram for energy.

Better prompt:

Create a left-to-right Sankey diagram showing 100 TWh primary energy. Split into 45 TWh electricity generation, 35 TWh transport fuel and 20 TWh direct heating. From electricity generation, show 28 TWh useful electricity and 17 TWh heat loss. Use proportional band widths and label every flow with TWh.

Research-Ready Checklist

Before the diagram goes into a paper or a talk, run through this:

• Are all the flow widths proportional?
• Are the units visible?
• Are small categories grouped sensibly?
• Is the direction clear?
• Does the caption explain the data source and time period?
• Do the colors carry meaning rather than just decorate?
• Does the figure still read once it's resized to journal column width?

FAQ

What is the difference between a Sankey diagram and a flowchart?

A flowchart shows the order of a process. A Sankey diagram shows quantitative flow between stages, and the width of each band carries the data.

Can I use a Sankey diagram in a research paper?

Yes, as long as the data are quantitative and the flows are meaningful. They're common in energy, environmental science, systems engineering, material flow analysis and cohort tracking.

What data do I need for a Sankey diagram?

At a minimum, source, target and value columns. Units and stage labels make the diagram far easier to interpret.

Get a first draft going with the SciDraw AI Sankey Diagram Generator.