59 The Water Cycle-High

The Water Cycle Written by Robert N. Knight

《水循环》罗伯特·N。 骑士

Introduction People call Earth the "water planet" because water covers three-fourths of its surface. We have lots of water, but most of it we can't use. The world population is growing, and as it grows, more people compete for this supply of water. Also, as we pollute more of our water supply, the water we need is getting scarcer. This book explores how Earth's water moves from place to place. It describes the changes water undergoes as it moves. It also describes how we use water and what we can do to conserve and protect it.

人们称地球为“水行星”，因为水覆盖了地球表面的四分之三。 我们有很多水，但大部分都不能用。 世界人口在增长，随着人口的增长，越来越多的人争夺这种水的供应。 此外，随着我们对水源的污染越来越严重，我们所需的水也越来越少。 这本书探讨了地球上的水是如何从一个地方移动到另一个地方的。 它描述了水在流动时所经历的变化。 它还描述了我们如何使用水，以及我们可以做些什么来节约和保护它。

About 95 percent of Earth's water is contained in the oceans that cover most of the planet's surface. Ocean water contains many kinds of minerals. These minerals give ocean water its salty taste, which is why it is called salt water. Drinking salt water just makes you thirstier. People and many other animals can get sick or die if they drink too much salt water. About 3 percent of Earth's water is fresh water. Lakes, rivers, and streams all contain fresh water that comes from rain and melted snow. Fresh water also exists underground. But most of Earth's fresh water is contained in glaciers found in mountains as well as icebergs and ice sheets found around the North and South Poles.

地球上大约95%的水存在海洋中，海洋覆盖了地球的大部分表面。 海水含有多种矿物质。 这些矿物质使海水具有咸味，这就是为什么它被称为盐水。 喝盐水只会让你更渴。 人和许多其他动物如果喝了太多的盐水就会生病或死亡。 地球上大约3%的水是淡水。 湖泊、河流和小溪都含有来自雨水和融雪的淡水。 地下也有淡水。 但地球上的大部分淡水都包含在山区的冰川中，以及北极和南极周围的冰山和冰原中。

The Movement of Water Matter is found in three states: liquid, solid, and gas. We are used to seeing Earth's water in its liquid state. Water also exists in its solid state as ice and in its gas state as invisible water vapor. Earth's water often changes from one state of matter to another as it moves from place to place. The changes and movement of Earth's water are all parts of the water cycle. The water cycle has been going on for billions of years, moving Earth's water from the oceans to land and back to the oceans.

水物质的运动有三种状态:液体、固体和气体。 我们习惯于看到地球上的水处于液态。 水也以冰的固态存在，也以看不见的水蒸气的气态存在。 地球上的水在从一个地方移动到另一个地方时，经常从一种物质状态转变为另一种物质状态。 地球上水的变化和运动都是水循环的组成部分。 水循环已经持续了数十亿年，将地球上的水从海洋转移到陆地，再转移到海洋。

Energy from the Sun powers the water cycle. This energy helps water change from one state to another. The water cycle begins with evaporation. During evaporation, liquid water changes into invisible water vapor. Heat and light from the Sun hit Earth's water in oceans, rivers, lakes, and even the smallest puddles. The tiny particles that make up water, called water molecules, absorb this energy. As they gain more and more energy, the molecules move faster and faster and begin to spread apart. Soon they absorb enough energy to escape Earth's surface water and enter the air as water vapor.

来自太阳的能量为水循环提供动力。 这种能量帮助水从一种状态转变为另一种状态。 水循环从蒸发开始。 在蒸发过程中，液态水变成看不见的水蒸气。 来自太阳的光和热撞击着地球上的海洋、河流、湖泊，甚至是最小的水坑中的水。 构成水的微小粒子，即水分子，会吸收这种能量。 当它们获得越来越多的能量时，分子移动得越来越快，并开始散开。 很快，它们就吸收了足够的能量，以水蒸气的形式脱离地球表面的水进入空气。

When water vapor in the air rises into the atmosphere, it begins to cool. Water molecules begin to collect on dust particles floating in the air. They gather to form tiny water droplets. This process, called condensation, happens whenever water changes from a gas back to a liquid. This is the next step in the water cycle. As more and more water vapor condenses, the droplets start to form clouds. As more droplets form, the clouds get thicker and darker. You can tell a lot about what weather might be coming by looking at clouds. High, wispy clouds mean there is ice and moisture above, and the weather may be changing. Fluffy, spread-out clouds may mean there is a little water above, but not enough for rain. Very tall clouds with dark bottoms usually mean that a thunderstorm with heavy rain is coming.

当空气中的水蒸气上升到大气中时，它开始冷却。 水分子开始聚集在空气中漂浮的尘埃颗粒上。 它们聚集在一起形成微小的水滴。 这个过程被称为冷凝，每当水从气体变回液体时就会发生。 这是水循环的下一步。 随着越来越多的水蒸气凝结，水滴开始形成云。 水滴越多，云层就越厚越黑。 你可以通过观察云层来预测天气。 高而稀疏的云意味着上面有冰和水分，天气可能会发生变化。 蓬松、散开的云层可能意味着上面有一些水，但不足以下雨。 非常高的云层和黑暗的底部通常意味着雷暴和大雨即将来临。