Meet the people trying to help. Animals Whales eat three times more than previously thought. Environment Planet Possible India bets its energy future on solar—in ways both small and big. Environment As the EU targets emissions cuts, this country has a coal problem. Paid Content How Hong Kong protects its sea sanctuaries. History Magazine These 3,year-old giants watched over the cemeteries of Sardinia. Magazine How one image captures 21 hours of a volcanic eruption.
Science Why it's so hard to treat pain in infants. Science The controversial sale of 'Big John,' the world's largest Triceratops. Science Coronavirus Coverage How antivirals may change the course of the pandemic. Science Coronavirus Coverage U. Travel A road trip in Burgundy reveals far more than fine wine. Travel My Hometown In L. Travel The last artists crafting a Thai royal treasure. Subscriber Exclusive Content.
Why are people so dang obsessed with Mars? How viruses shape our world. The era of greyhound racing in the U. See how people have imagined life on Mars through history. See More. United States Change. In this situation the SOI is strongly positive, and the trade winds blow strongly across the warm Pacific, picking up plenty of moisture Figure 4a.
On the other hand, when the ocean surface off the coast of South America is abnormally warm, the air pressure between the eastern and western Pacific equalises or becomes a negative value, weakening or reversing the trade winds. In Australia this usually results in below average rainfall, and if this trend persists we can slip into drought. For example, when the SOI is consistently strongly positive i. When the SOI is consistently strongly negative we risk entering into periods of drought Figure 4c.
In Queensland, average annual rainfall ranges from very low values in the southwest, to very high values exceeding mm per year along the coast Figure 5. However, even in those areas with generally low rainfall, relatively heavy rainfall will occur in some years, causing flooding Figure 6.
Long-term climate change and variability may also be having an influence on rainfall a matter addressed in Question 8. When rain falls on a catchment, the amount of rainwater that is converted into flow down rivers and other waterways depends on the characteristics of the catchment.
Some rainfall is captured : A portion of the rain that falls on a catchment is captured by soil and vegetation. Generally, the more rain that falls in a particular area in a given period of time, the lower the proportion that can seep into the ground or be stored on the surface. The greater the rainfall intensity, the greater the potential for runoff. How long it rains, and the area covered by the rain, are also important. The more vegetation there is in an area, the greater the amount of rainfall that is captured and the less water there is available to flow over the surface.
Natural and artificial storages like farm dams and rainwater tanks have a similar effect in reducing runoff. The soil types in a catchment, land use and weather conditions prior to a rainfall event are also important as they control the amount of rainfall that can infiltrate into the soil, and hence the amount of rainfall which becomes flow.
If a large storm is preceded by a period of wet weather, then the ground has little capacity to absorb further rainfall, and a higher proportion of the rainfall will flow across the land surface and into waterways.
The construction of areas that cannot absorb water, such as roofs and roads, will also result in reduced infiltration and more rainfall being turned into runoff. Rainfall that is not captured enters the waterways: Once water begins flowing in a catchment, various factors determine how much flows downhill into successively larger waterways, and how quickly it moves.
Typically,larger catchments result in greater streamflow if widespread rainfall occurs for a long time. The steeper the catchment area, the faster the runoff will flow. Floods are also affected by the roughness of the terrain being passed over. Dense vegetation and artificial obstacles such as fences and houses will slow down water flow, often leading to lower flood levels downstream.
Swamps and natural ponds or lakes have the capacity to store floodwater and release it slowly. Artificial structures such as dams or detention basins small reservoirs can also store water for a period of time, and reduce the peak of downstream flows while extending the duration of an event. All such structures have a finite capacity and there is a limit to the volume of catchment flow that can be stored. They can also send a rush of water from the ocean onto coastlines in an event called a storm surge, which floods low-lying areas.
Learn more about how hurricanes form. Florence dropped nearly 36 inches of rain in Elizabethtown, North Carolina, and led to widespread flooding throughout the Carolinas. Credit: NOAA. Another phenomenon that can cause extreme rainfall is called an atmospheric river. Atmospheric rivers are long, narrow conveyor belts of moisture that move through the atmosphere.
Strong atmospheric rivers can deliver enormous amounts of rain and snow in California, the Pacific Northwest and Alaska, especially during the winter months. This can lead to serious flooding and mudslides. The ABI can also determine the amount of total moisture in the atmosphere from the ground all the way to the top of the atmosphere.
This provides useful information for weather forecasters to improve predictions for heavy rains and flash flooding and help people stay safe.
After flooding occurs, weather satellites can also be used to spot heavily flooded regions from space. This flood map shows the impact of Hurricane Irma in Florida on Sept.
0コメント