The United States is known for having a varied climate. This is largely due to changes in latitude and whether there are mountains, deserts, or other prominent landscape features.
In 2021, the average rainfall across the United States was 30.48 inches. However, due to the different climates across the States, the recorded rainfall across the country can vary dramatically.
Methods for measuring rainfall have evolved over time as systems and technology advance. Some methods record rain once it falls, whereas other systems measure precipitation from space.
In this guide, we'll look at how rainfall is measured, why it is important to record the changing precipitation levels, and the effects that rainfall can have on geographical areas.
There are different types of rain gauges, which are devices that can be used to measure how much rain has fallen in a period of time. Precipitation is usually measured by instruments such as the non-recording cylindrical container and the tipping bucket rain gauge.
Tipping bucket rain gauges can automatically collect rain through a funnel, which will then be directed into one of two buckets. Once the water hits the mechanism limit, the bucket will tip and hit the stop screw or calibration. This will activate a switch, which will electronically record the rate and frequency of the tipping.
After the first bucket tips, the rain will start filling the second bucket. The process of filling and tipping the buckets will continue until the rain stops. Ideally, the rain gauge information should be checked at the same time every day. It may be necessary to check and empty the tipping bucket rain gauge more frequently during heavy periods of rain to prevent the buckets from overflowing.
Rain gauges aren't necessarily the most accurate way of measuring rainfall. Depending on where they are positioned, there may be obstacles that prevent the correct level of rain from falling into the gauge. The wind could also redirect the rain and prevent it from fully falling into the gauge.
To improve the accuracy of precipitation measurements, there needs to be a dense network of measuring points to help record the true volume of rainfall in a given area. There are various techniques that are used by scientists to measure the average precipitation and convert them to areal estimates.
Rainfall can also be measured via radar, which can produce a detailed overview of precipitation over a large area. Radar systems can detect precipitation clouds and measure their structure and how they develop over time. The information gathered from radars is used to form weather forecasts for the coming days, weeks, and months.
A radar sends out electromagnetic pulses and records when it hits a target (such as a ship or a plane). To measure rainfall via radar, pulses are sent out and are used to reflect where it hits precipitation. A weather radar is the most accurate way to measure the intensity and location of rainfall.
Weather forecasters use weather radar to record precipitation data over large areas. The radars can also detect frozen precipitation (such as snow and hail), although they struggle to detect drizzle as the droplets are too small.
Rain is commonly measured in inches or millimeters, depending on whether a country uses the imperial or metric system of measurement. In the United States, rain is typically measured in inches.
Historically, the standard size for a rain gauge had a rim width of five inches, and the container was placed around 10 inches above ground level. After the container had been filled, the collected rainwater would be poured into a graduated glass rain measure. Some containers with a greater capacity were used at sites that had infrequent rainfall readings.
It's important to measure rainfall to monitor for potential droughts or floods. Both of these situations can cause devastating effects on the agricultural industry, as well as commercial sectors and domestic areas. By measuring rainfall, authorities can decide whether they need to adapt their use of reservoirs or advise citizens to cut back on their water use.
Understanding precipitation can also help weather forecasters prepare for natural disasters that are caused by extreme weather. Hurricanes, tornados, and other large storms can be predicted by studying rainfall patterns. The results can be used to help warn citizens about impending disasters and could potentially prevent casualties. Given enough time, authorities and citizens can also make the necessary travel arrangements or safety precautions to protect themselves, their homes, and their belongings.
Rainfall measurements can also be used to track weather changes, which can be used to measure global warming. On average, total precipitation has increased over land in the United States and the rest of the world at a rate of 0.04 inches each decade. In 48 states alone, precipitation has increased at a rate of 0.20 inches per decade. Without measuring the amount of rainfall each year, scientists wouldn't be able to track these changes.
Global Precipitation Measurement (GPM) is a project run by NASA that aims to observe the Earth's precipitation. The GPM department can measure raindrop sizes from space, which can help scientists to determine how big a storm may become, how much rain will be produced and how long a storm may last.
GPM can take three-dimensional snapshots of the distribution of raindrop size, which can help scientists understand the structure and behavior of storms. Scientists can accurately measure the precipitation from a storm cloud by observing the ratio of large raindrops to medium and small raindrops.
The size and distribution of raindrops in storm clouds can impact weather conditions. For example, smaller raindrops are more likely to evaporate, which will cool the air. This may produce strong winds as cool air is denser.
By knowing how large raindrops are, scientists can better predict wind strengths and patterns. Generally, larger drops tend to be positioned near the center of the storm, while smaller drops are located on the edge.
Understanding the size of raindrops can help to improve measuring techniques and accuracy. This, in turn, can help improve the prediction of weather patterns, floods, and storms.
The NOAA National Severe Storms Laboratory classes a thunderstorm as severe if it produces hail that is one inch or larger or if the wind gusts are greater than 50 knots (57.5 mph).
Around the world, there are an estimated 16 million thunderstorms every year. It's estimated that there are an average of 100,000 thunderstorms annually in the United States alone, 10% of which are considered 'severe'.
On average, the US sees 14 named storms between June and November, half of which are likely to become hurricanes. This type of storm is based solely on windspeed and does not take into consideration rainfall, storm surges, or tornados.
To be classed as a hurricane, a tropical tornado must have wind speeds of above 64 knots (74 mph) that are sustained at least 10 m above the surface.
If there is a lack of rainfall for a few weeks or months, it is considered a short-term drought. When the lack of precipitation lasts for over six months, it is considered a long-term drought.
The first sign that there may be a drought is based on recorded rainfall. It's difficult to measure the exact point that a drought begins, but a significant lack of rain can have an obvious and visual impact on agricultural areas.
Within a short while, the lack of rain will cause moisture levels in the soil to decrease. This can lead the surrounding vegetation to become dehydrated and potentially die. The lack of rainfall will also have an effect on streams and reservoirs in the area, although this may not be noticeable for a few weeks or months. Water levels in wells won't show a considerable shortage of rainwater for over a year after the drought first begins.
A single significant rainfall can provide immediate relief from previous drought conditions, although it will require multiple heavy periods of rain over the following months to fully break the drought.
Tropical storms can release enough rainwater to benefit dehydrated soils for several months. However, it's necessary that the rain patterns and levels return to normal in order to improve the conditions of nearby streams, reservoirs, and soils.
According to the NOAA-NCDC, Hawaii is the wettest state, with some areas recording over 300 inches of rainwater each year. This also makes the archipelago state one of the rainiest locations in the world.
However, despite the high levels of rainfall, NOAA has recorded decreasing precipitation in Hawaii over recent years. Since 2007, 10 of the 15 years had below-average wet season precipitation.
The changing levels of rainfall during Hawaii's annual wet seasons have contributed to a long-term drought on the island. The number of consecutive dry days in Hawaii has also increased since the 1950s.
More than 40% of Hawaiian islands experienced severe, extreme, or exceptional drought conditions in 2010, which led to a lack of usable water and increased fire risk. This increase in drought conditions is a continuing trend that has continued through the past 10 years.
In 2021, 66.84 inches of rainfall were recorded in Mississippi, the highest level of precipitation in the contiguous 48 states. Nevada was the driest contiguous state, with only 9.56 inches recorded in the same year.
Rainfall in the US varies depending on the season. The wettest months in most of the country are between October and April. Typically, November and December record the most rain, while July and August tend to be the dryest months in most states.
Scientists measure precipitation on a regular basis so that they can record rainfall patterns and levels. A standard rain gauge can be used to collect rainwater, which can help measure rainfalls in a given location. Weather radars can more accurately estimate rainfall based on storm clouds and the intensity of the predicted precipitation.
Measuring rainfall is a reliable way to record the average precipitation for various locations and seasons of the year. This data can be used to understand weather patterns and can help scientists to understand and prepare for periods of excess precipitation or drought.