Imagine a tropical rainforest without any rain. It wouldn’t be much of a rainforest, right? All plants need water to grow, and without it, they would dry up and die. There’s an old Hawaiian saying, “Hahai no ka ua i ka ulula`au,” which means “the rain follows after the forest.” But how does that work?
All plants lose water when they open tiny pores on their leaves during photosynthesis, a process where they make food using sunlight. This loss of water pulls more water up through the plant’s stem. In rainforests, there’s so much rain that the soil is always wet, providing plenty of water for the trees. This means rainforest trees can afford to lose more water than other plants.
The water vapor that rises from the forest helps form clouds filled with moisture. This, along with the warm air rising, speeds up the formation of rain. The rain then falls back to the soil and is absorbed again, continuing the cycle. This cycle—absorption, evaporation, rain—happens wherever there are plants. However, in rainforests, the combination of wet soil, fast-growing trees, and the hot tropical sun makes this cycle happen much faster. Unlike other places where clouds might drift away, in rainforests, the water stays in the same area.
If the forest didn’t release so much water into the air, rainforests wouldn’t be as rainy. And without the rain, the forest couldn’t release as much water into the air. So, which came first, the rain or the rainforest?
Before rainforests existed, the land was covered by trees like cypress, pine, and spruce. These trees were careful with their water use, which meant the air was drier and there was less rain. But about 130 million years ago, a new type of plant evolved—flowering plants. These plants took the risk of losing more water to grow faster, which helped them outcompete the older trees and take over tropical regions.
Flowering plants, or angiosperms, lost so much water into the air that they brought their own rain with them as they spread. Today, tropical rainforests get more rain than if they were covered by pine forests—up to a meter more each year. This is like having an extra two and a half hours of heavy rain every week. This extra water also cools the forest, which is why the Amazon isn’t as hot as the Sahara Desert or even some forests in Texas during summer.
However, the hot, dry tropics of the past might become our future. In parts of the Amazon where large areas of rainforest have been cut down or cleared for farming, weather stations are already noticing less rain, and forest fires are happening more often. Scientists worry that these changes could lead to hotter, drier, and more flammable tropics in the coming decades, making it harder for both the remaining forest and the people living there.
So, when thinking about how to help during a drought, consider planting a tree. Seriously—Hahai no ka ua i ka ulula`au.
Conduct a simple experiment to understand the water cycle. Fill a clear container with water and cover it with plastic wrap. Place it in a sunny spot and observe how water evaporates, condenses, and eventually forms droplets. Record your observations and relate them to how rainforests maintain their own water cycle.
Create a diorama of a rainforest ecosystem. Include elements like trees, clouds, and rain to demonstrate the relationship between the forest and rainfall. Use materials like paper, clay, or recycled items. Present your diorama to the class, explaining how the rainforest contributes to its own climate.
Participate in a role-playing game where each student takes on the role of a component in the rainforest ecosystem, such as a tree, rain cloud, or animal. Act out the water cycle and discuss how each role contributes to the rainforest’s climate and health.
Research how flowering plants have influenced the climate over millions of years. Present your findings in a report or presentation, highlighting how these plants helped create rainforests and how they continue to impact the environment today.
Organize a tree-planting event at your school or in your community. Learn about the types of trees that are best suited for your local climate and how planting trees can help combat climate change. Reflect on the Hawaiian saying, “Hahai no ka ua i ka ulula`au,” and discuss its relevance today.
Here’s a sanitized version of the provided YouTube transcript:
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A tropical rainforest without rain wouldn’t be much of a rainforest. All plants need water to grow, and without it, they wither and die. This brings to mind the ancient Hawaiian proverb, “Hahai no ka ua i ka ulula`au,” which means “the rain follows after the forest.” How could that be?
All land plants lose water when the pores on their leaves open during photosynthesis, and this evaporation draws more water up through their stems. In rainforests, with so much rain soaking the soil, water is nearly unlimited. Consequently, rainforest trees can afford to lose more water than other plants.
The water vapor rising from the forest feeds moisture-laden clouds, and this process, along with convection, accelerates the formation of rain. This rain falls to the soil and is absorbed again. This cycle—absorption, evaporation, rain—occurs wherever there are plants. However, the combination of super-wet soil, fast-growing trees, and the hot tropical sun makes this cycle much faster in the rainforest. Unlike other biomes, where clouds might form in one area and rain in another, the water stays in the same region.
Without the forest pumping so much water into the air, rainforests wouldn’t be as rainy. And without that rain, the forest couldn’t pump as much water into the air. So, which came first, the rain or the rainforest?
Before rainforests, ancestors of trees like cypress, pine, and spruce dominated the land, but they were conservative with water use, leading to drier air and less rain. However, around 130 million years ago, a new type of plant evolved that took the risk of losing more water for enhanced photosynthesis—these were the flowering plants. Their faster growth allowed them to outcompete the ancestral pines and take over tropical regions.
Angiosperms lost so much water into the air that as they spread, they brought their own rain with them. Today, tropical rainforests receive more rain than if they were replaced by pine forests—by as much as a meter more each year, which is equivalent to an extra two and a half hours of heavy rain every week. This abundance of water also cools the forest, which is why the Amazon isn’t as hot as the Sahara or even an east Texas pine forest in summer.
However, the hot, dry tropics of the past may soon become our future. In parts of the Amazon where large areas of rainforest have been logged or cleared for agriculture, weather stations are already observing decreased rainfall, and forest fires have become more frequent. Scientists are concerned that these changes will lead to hotter, drier, and more flammable tropics in the coming decades, making it tougher for both the remaining forest and the people who live there. So, when facing drought, consider planting a tree. Seriously—Hahai no ka ua i ka ulula`au.
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This version maintains the essence of the original transcript while removing any informal language and ensuring clarity.
Rainforest – A dense forest rich in biodiversity, typically found in tropical areas with consistent heavy rainfall. – The Amazon rainforest is home to thousands of plant and animal species, making it one of the most diverse ecosystems on Earth.
Water – A vital resource for all living organisms, essential for processes like hydration, nutrient transport, and photosynthesis. – Plants absorb water through their roots to help them grow and perform photosynthesis.
Cycle – A series of events that are regularly repeated in the same order, such as the water cycle or the life cycle of a plant. – The water cycle includes processes like evaporation, condensation, and precipitation, which help distribute water across the planet.
Photosynthesis – The process by which green plants and some other organisms use sunlight to synthesize foods with the help of chlorophyll. – During photosynthesis, plants convert carbon dioxide and water into glucose and oxygen, providing energy for themselves and oxygen for other organisms.
Moisture – The presence of a liquid, especially water, often in trace amounts, which is essential for plant growth and survival. – The moisture in the soil helps seeds germinate and supports the growth of young plants.
Trees – Large perennial plants with a trunk, branches, and leaves, which play a crucial role in producing oxygen and providing habitats. – Trees in the forest absorb carbon dioxide and release oxygen, helping to maintain the balance of gases in the atmosphere.
Climate – The long-term pattern of weather conditions in a particular area, including temperature, precipitation, and wind. – The climate of a rainforest is typically warm and humid, with frequent rainfall throughout the year.
Angiosperms – Flowering plants that produce seeds enclosed within a fruit, making them the most diverse group of land plants. – Angiosperms include a wide variety of plants, from grasses to flowering trees, and are crucial for many ecosystems.
Drought – A prolonged period of abnormally low rainfall, leading to a shortage of water that affects plants and animals. – During a drought, plants may wilt and die due to the lack of sufficient water to sustain their growth.
Soil – The upper layer of earth in which plants grow, composed of organic matter, minerals, gases, liquids, and organisms. – Healthy soil is essential for agriculture, as it provides nutrients and support for crops to grow.
