National Drought Mitigation Center

What is Drought?

During a drought, ponds, lakes and rivers may begin to dry up.

What do you think of when you hear the word drought? Do you think “dry,” “hot,” “dusty,”  “cracked earth,” or even “no water”? If so, you’re on the right track! 

When some places are in a drought, they may be dry, hot and dusty; cracks may appear in the soil, and rivers, lakes, streams, and other sources of water may go dry. Other places in drought get some rain, but not as much as they usually receive during that season. A drought means that a place has less precipitation (rain or snow) than normal over a few months or even longer.

What causes a drought?

In order to answer to that question, let's explore the connections between weather, climate, the water cycle and drought. 

Weather and Climate

If you look outside right now, do you see sunshine, or mostly clouds? Is it windy? Is it hot or cold? Whatever your answers to those questions are, that is your weather for today. Weather can be defined as the conditions experienced in a place over a brief period of time, like day-to-day or even over a week.

When you hear or read a weather forecast, you may hear the word normal. The weather forecaster may say, “today will be warmer than normal” or “we are having below normal precipitation.” Weather that we expect or know to be “normal” for a place is one way to define climate. 

So, in other words, climate is a place’s weather over a longer period of time, like months, seasons, and years. What is normal for a place depends on its elevation (how high above sea level it is), how close it is to the oceans or other large bodies of water, and its latitude (how close or far it is from the equator). 

A place’s climate can change slightly from year to year or decade to decade. This is what we call natural climate variability. Because these changes or variations can occur, we consider drought to be a normal part of climate just like floods, hurricanes, blizzards, and tornadoes. 

Water Cycle

Water covers more than 80 percent of the earth’s surface. It is found in oceans, lakes, rivers, and even ice caps and glaciers. Water is also found underground in aquifers. The water that exists today is the same water that existed billions of years ago. This is because water is what we call a limited renewable resource

Water is a renewable resource because it travels through the oceans, rivers, ground, and atmosphere; it is always moving! It falls from the sky as rain or snow into our oceans, lakes, and rivers and onto land. Precipitation that falls on the land enters the groundwater through percolation or travels to streams, rivers, and lakes as runoff. Water in streams and rivers is carried to the oceans, where it evaporates and forms clouds—where the cycle starts all over again!

Water is also a limited resource. We will always have the same amount of water on the earth, but we can't always use as much as we need. One reason is that 97 percent of the earth's water is saltwater, and saltwater is not good for people and wildlife and many plants. Of the remaining 3 percent, which is freshwater, nearly 75 percent is frozen in glaciers, making it unavailable to us. Another reason that water is a limited resource is that pollution, increased human demand for water, and changes in precipitation patterns can decrease both the quality and amount of water available to people, plants, and wildlife.

Water and Weather on the Move

Water evaporating from the oceans, lakes, rivers, and streams moves to the atmosphere. Air carries the moisture up, and if conditions are right, it forms clouds. Wind moves these clouds around the globe. The wind that carries the clouds that bring rain is called the jet stream. The jet stream changes its pattern with each season. In other words, the jet stream will carry weather patterns, such as precipitation and temperature, in different directions or over different routes during each season. Think about four different routes you could take to a friend’s house, and during each season you would take a different route—that's what the jet stream does.

If the jet stream changes its pattern or is blocked by “ridges” or “troughs” of air in the atmosphere, the normal weather for a place can be much different for a period of time. It’s almost as if the jet stream has hit a road block or taken a detour!

When the jet stream hits a road block or takes a certain detour and is not bringing the clouds that produce rain, a drought can occur. These patterns in the jet stream could change for many reasons. Scientists are still uncovering the answers, but many think that influences such as differences in the amount of snow and ice cover, the amount of vegetation (trees or grasses) covering the land, the moisture in the soil, and ocean surface temperature and currents can cause these patterns to change.

Causes of Drought

Drought has many causes. It can be caused by not receiving rain or snow over a period of time. We learned in the discussions about the water cycle and weather that changes in the wind patterns that move clouds and moisture through the atmosphere can cause a place to not receive its normal amount of rain or snow over a long period of time.

If you live in a place where most of the water you use comes from a river, a drought in your area can be caused by places upstream from you not receiving enough moisture. There would be less water in the river for you and other people who live along the river to use. 

People can also play a big role in drought. If we use too much water during times of normal rainfall, we might not have enough water when a drought happens.

Drought and Floods

Earlier we learned that droughts are normal parts of climate just like floods, hurricanes, and tornadoes. That might sound strange to you if you have seen pictures of what floods, tornadoes, and hurricanes can do to houses, trees, and the land. Droughts, floods, hurricanes, and tornadoes are what we call natural hazards

We usually can't see drought coming. We can see water rising in a river, watch the wind pick up as a hurricane approaches, or see thunderclouds approaching. We also can turn on the television, radio, or internet to see storms on radar and find out what we should do to protect ourselves from storms. We don’t have watches or warnings for drought like we do for other natural hazards such as tornadoes, floods, or hurricanes. 

Drought doesn’t have a clear beginning and end like tornadoes or hurricanes or floods. It starts and ends slowly and often we don’t see the effects of drought for weeks, months, or even years. This is why we often say that drought is a creeping natural hazard.

Drought can sneak up on us because we might enjoy being outside in the sunshine and not having rain interrupt our plans. We can have several weeks of enjoying the sunny weather before we notice that our lawns or plants start to look brown. We can even go for months before we notice that there isn’t as much water in a nearby lake. It doesn’t take weeks or months to notice the effects of floods, tornadoes, or hurricanes, does it?