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Listen to part of a lecture in an environmental science class. The professor is discussing the role of wetlands in flood control. "Now, many people think of wetlands as just muddy, mosquito-infested areas that are good for wildlife, but they actually play a critical role in flood prevention. Wetlands act like natural sponges. When heavy rain falls, they absorb and slowly release water, reducing the peak flow that would otherwise rush into rivers and streams. In fact, a study in the United States found that wetlands can reduce flood heights by up to 60 percent in some areas. This is particularly important in regions where urbanization has increased impervious surfaces, like roads and rooftops, which prevent water from soaking into the ground. Instead, water runs off quickly, causing flash floods. By preserving and restoring wetlands, we can mitigate these risks. However, many wetlands have been drained for agriculture or development. In the past century, we've lost over half of our original wetlands. So, restoring them isn't just about biodiversity; it's a practical flood management strategy that saves money and lives." Now, the professor mentions a statistic about wetlands reducing flood heights. What does this statistic illustrate?