Global Climate Change

For more information on changes in global precipitation, visit: EPA Global Warming Site: Trends

Remote Sensing: Precipitation

Precipitation is a very important part of climate. Precipitation is the solid, liquid, or gaseous water that falls from the atmosphere to Earth's surface. This includes snow, sleet, hail, rain, and even mist. Changes in the amount of precipitation falling to Earth affect our lives in many ways. Daily human activities, business and industry, agriculture, and the environment all require water. Much of Earth's water ultimately
comes from precipitation. Too little precipitation can result in dry soil, shallow streams, and shortages of municipal water supplies.

However, too much precipitation can also have a negative impact on human activities, business and industry, agriculture, and the environment. For example, too much rain or snowmelt (water from melted snow) at one time can lead to flooding. Living organisms, including crops, can drown in floodwaters.
Homes, businesses, even land can be washed away.

Image of a map that displays precipitation trends from 1900 to the present. Please have someone assist you with this. For these reasons, many scientists have been monitoring precipitation trends. That is to say, they have been watching changes in the amount of precipitation falling to Earth. In the last 100 years, precipitation has increased by an average of about 1% over all the land surfaces on Earth. Across the United States, alone, precipitation has increased by an average of about 5% in the last 100 years. Note that this is an average. Some areas of the United States have experienced as much as a 20% increase in precipitation over the last 100 years (see figure above). While other areas have experienced a 20% decrease in precipitation. Map courtesy of the United States Environmental Protection Agency.

There are many reasons for changes in precipitation. The leading cause is a change in temperature. Many scientists believe an increase in temperature could lead to a more intense water cycle. The rates of evaporation from soils and water, as well as transpiration from plants, could increase. The amount of precipitation could also increase.

Predicted changes in the water cycle differ according to the region of the planet being examined. Many scientists believe rates of evaporation will be greater than precipitation in the middle latitudes such as the United States. This could result in drier summers in these regions.

Of course predicted changes in the water cycle also differ according to the climate model used. The "business as usual" climate model (described in Remote Sensing: Carbon Dioxide" assumes climate changes based solely on the effects of greenhouse gases. Predictions of changes in precipitation based on this model show an increase in the amount of precipitation falling in the next 100 years (see figure below). Another model includes in its assumptions the effects of sulfates. Sulfates cause a cooling of the atmosphere. Therefore, sulfates can decrease the effects of greenhouse gases on temperature. Models of future precipitation that include the effects of sulfates also show an increase in the amount of rain and snow. However, the increase in precipitation predicted in these models is not as great as the increase predicted in the "business as usual" models.

Graph courtesy of the International Panel of Climate Change.

Image of a graph that displays the annual global precipitation. Please have someone assist you with this.

Whether or not the amount of precipitation changes, many climate models show that the timing of precipitation will change. Scientists predict that most precipitation in the future will fall during a smaller number of storms that are heavier in intensity. This is because the elevated temperatures will provide more energy in the atmosphere for storm production.

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