Question 129·Hard·Command of Evidence
River Basins Grouped by Change in Annual Maximum 1-Day Rainfall Under Two Ocean Temperature Conditions, by Percentage of Basins
Because warm ocean water can add moisture to the atmosphere, climate scientists often examine how ocean temperature affects the intensity of extreme precipitation. M. Patel and colleagues used a climate model to compare thousands of river basins under one scenario with present-day sea surface temperatures and another with sea surface temperatures uniformly warmer by 2°C. They then categorized each basin by how the basin’s annual maximum 1-day rainfall changed in the model.
The team concluded that under the warmer-ocean scenario, the percentage of basins experiencing an increase of more than 10% in annual maximum 1-day rainfall will be higher than under present-day conditions.
Which choice best describes data in the graph that support Patel and colleagues’ conclusion?
For command-of-evidence questions that refer to a graph, restate the conclusion in your own words and underline any threshold words (like “more than 10%”). Then look only at the graph elements that directly match those words and compare the relevant bars across conditions. Finally, choose the option that reports that specific comparison without switching categories, combining categories, or adding an extra claim the graph does not show.
Hints
Match the category to the conclusion
The conclusion is not about rainfall in general; it’s about more than a 10% increase. Focus only on that x-axis category first.
Compare the two scenarios within that category
Read the heights of the two bars in the “More than 10% increase” group and note which scenario has the larger percentage.
Prefer the choice that is most specific
If more than one option describes a true pattern, choose the one that most directly addresses the conclusion’s exact threshold (more than 10%).
Step-by-step Explanation
Identify what must be supported
The conclusion claims that the percentage of basins with more than a 10% increase in annual maximum 1-day rainfall is higher under the warmer-ocean scenario than under present-day conditions.
Find the relevant bars
In the graph, look at the “More than 10% increase” category and compare the two bars (present-day vs warmer ocean).
Compare the percentages and select the matching choice
The “More than 10% increase” bar is just under 20% for present-day conditions and about 70%+ for the warmer-ocean scenario, so the best supporting choice is:
Under present-day ocean temperatures, just under one-fifth of basins show more than a 10% increase in annual maximum 1-day rainfall, but under the warmer-ocean scenario, nearly three-quarters of basins do.