فارسي | English
  About Us | About Iran | Contact Us | Staff Info[Geoportal Info] [Maps] [Mining Info] [Other Activities]  
 
  News | Events | Photo Gallery | Downloads | Links | Kids  Search    Region    Scale    Subject   :Access to information by   Home | Newest   
 

New titles:
 Is the next gold mine in Bulgaria
 A Closer Look at an Undersea Source of Alaskan Earthquakes
 More than 210 killed by earthquake in Iran-Iraq border region
 Four systems out there and hurricane season hasn't even hit its peak yet
 NASA Flights Gauge Summer Sea Ice Melt in the Arctic
 Indonesian Cave Reveals Nearly 5,000 Years of Tsunamis
 Down to Earth With: Cave microbiologist Hazel Barton
 When a big earthquake hits, your first instinct can mean life or death
 What Caused the Ongoing Flooding on Lake Ontario?
 Short Rains and Long Rains
News Report
 
Short Rains and Long Rains
1396/07/24
NGDIR News Section-- A recent paper in Reviews of Geophysics examined the drivers of interannual and regional rainfall variability in eastern Africa.
  
   We tend to hear about the climate of eastern Africa when it makes the news headlines, either for a severe drought or floods, both of which can be devastating for local populations, their crops and wildlife. A recent review article published in Reviews of Geophysics gave an overview of the current state of knowledge on the region's rainfall regime, and its temporal and spatial variability. The editors asked the author to explain the main characteristics of the climate of eastern Africa and describe where further research efforts are still needed.
  
   Does the annual migration of the Intertropical Convergence Zone (ITCZ) affect rainfall over eastern Africa?
   No, it does not. The ITCZ is best developed over the ocean. Such a convergence zone is evident over northern Africa, but it lies well north of eastern Africa throughout the year. Over the equatorial regions of Africa, a seasonal migration of the tropical rainfall zone is evident, producing the seasonal cycle in eastern Africa. However, it is not manifested as a low-level zone of wind convergence. The factors enhancing rainfall during the two main rainy seasons, and producing aridity during the other seasons, are much more complex and not yet completely understood.
  
   What kind of extreme climate events does the region experience?
   Eastern Africa faces some of the most extreme climatic events in the world. This includes not only devastating droughts, but also extreme flood conditions, sometimes within the same year. The most extreme flood occurred in 1961; Lake Victoria rose several meters and November rainfall in northern Kenya was several times the annual mean. In contrast, during the 2010/11 drought rainfall was at least 50 to 75 percent below the long-term mean in Kenya, southern Somalia, and southern Ethiopia. Yet, high rainfall in November of 2009, January of 2010, and November of 2011 produced flood situations.
  
   Has the occurrence of extreme climate events changed over recent years?
   Extreme climatic events in eastern Africa have increased in both frequency and severity in recent years. Droughts have become longer and more intense, and they now tend to continue across rainy seasons. They also appear to be affecting both the northern areas, where rainfall occurs primarily in the boreal (Northern Hemisphere's) summer, and the equatorial regions, with two rainy seasons during the boreal spring and autumn. At the same time, interannual variability has increased, producing unusually strong floods in the region. Overall, however, there is a general increasing tendency in the rains of the boreal autumn (the "short rains"), but a decline in the rains of the boreal spring (the main, "long rains" season).
  
   What are the main drivers of year to year rainfall variability and extreme events.
  
   The main drivers are distinct for the three rainy seasons (summer, "long rains", "short rains"). In the summer rainfall region (northeastern area), El Nino plays a major role in the summer rainfall region, but low- and mid-level westerly flow, a strong Somali Jet, and a strong Tropical Easterly Jet also enhance rainfall.
  
   The main factor in the "short rains" is the intensity of the Walker cell in the central equatorial Indian Ocean, an atmospheric circulation system which in turn has some association to both the El Nino Southern Oscillation and the Indian Ocean Zonal Mode. The drivers of the "long rains" have been less definitely established, but the Madden-Julian Oscillation and the relative temperature of the tropical Pacific and Indian Oceans appear to be very important.
  
   How can prediction of climate variability be improved?
   Predictability is already high for the "short rains". For the long rains it could be improved by considering each month of the season separately and by producing individual forecasts for smaller sectors within eastern Africa. Further improvement can also be achieved by taking atmospheric variables (as opposed to sea surface temperature and other surface variables) into consideration in forecast models.
  
   Where is additional research needed to improve understanding in this field?
   A major unresolved question is the factors producing drought during the "short rains" season. Four factors have been shown to act jointly to produce the major flood events. However, droughts are usually associated with a single factor. In roughly half of the drought years, none of the four factors played a role. Overall the primary drivers change over time, so that another unresolved question is what produces these shifts in control. A related question is why the coupling of the "short rains" to large-scale factors marked decreased after 1982. Further research is also needed to better understand the processes that produce the seasonal cycle of rainfall in eastern Africa.
  
   By EOS

 
 
Publications  Library
Glossary  Papers
 
 
 
 
FAQ  Members
Job Offer  Training
 
 
 
 
• NanoBioEarth Database 
• Medical Geology Database 
• Geological Atlas of Roads 
• 4th National Development Plan 
• Marine Geology 
• Geography information 
• Mines and Deposits of Iran 
• Landslide Database of Iran 
• Exploration Area DB 
• Copper Database 
• Gold Database  
• Geoscience Laboratories 
• Mineral Information 
• Bibliographic Database 
• Geochemistry Database 
• Earthquake database 
• Abandoned mines DB of Iran 
• Mineral processing database 
• Minerals database 
 
 
 
 
Login Name:
Password:
Sign Up for membership ]
 
 
 
   Others Activities:• Geo Hazard Of South Caspian • Geoscience database of ALBA • Geoscience Database of ECO 
• GEOLOGICAL SURVEY OF IRAN • Tajikistan Geoscience Database • Geo Database of Venezuela • 4th National Development Plan 
• Export & Import Regulation Act     
 
 
Maps:• Map of Iran's Last Earthquake • Distribution Map of mineral Processing Plants 
• Mineral Distribution Map of Iran • Geosciences laboratories distribution map of Iran • Orohydrographic Map of Iran 
• Select state on iran map • Geological Map of Iran(1:1000, 000 Scale) • 2500 K Magnetic Lineament Map of Iran 
• Map of Iran's Earthquake    
 
Best viewed:1024*768
National Geoscience Database Of IRAN
URL:www.ngdir.ir
Contact Mail:Info@ngdir.ir
 
 
 Search with:           
Designed by Payvand Software Group  Privacy | Copyright | Disclaimer