5-May-2019: Rapid drying of Northeast India
Northeast India, one of the wettest places on the Earth has been experiencing rapid drying, especially in the last 30 years. Some places which used to get as high as 3,000 mm of rain during the monsoon season have seen a drop of about 25-30%.
A team of researchers from the Indian Institute of Tropical Meteorology, Pune, and Assam University set out to understand whether this decline is caused by anthropogenic activity or is it part of natural changes. The results published recently in JGR-Atmospheres show that the decreasing monsoon rainfall is associated with natural changes in the subtropical Pacific Ocean.
Pattern of fluctuations: Changes in the Pacific decadal oscillation (PDO) — a pattern of fluctuations in the ocean, particularly over the north Pacific basin — are mainly associated with this declined rainfall. Like El Nino/La Nina in the tropical Pacific, PDO has a signature for a longer time (on the decadal scale) in the sea surface temperatures and its interaction with the atmosphere, which in turn affects the northeast Indian summer monsoon.
Natural and manmade: The team used observed rainfall and sea surface temperature data for the period 1901-2014 for the study. The results show out that the reduction in rainfall during a major part of the last 114 years may be associated with global man-made factors, while the trend during the last 36 years is associated with natural phenomena.
Only about 7% of the rainfall in this region is associated with local moisture recycling, which means that anthropogenic activities can affect only this small percentage. So we concluded that the recent rapid drying is a part of interdecadal variability of monsoonal rainfall which is strongly associated with the PDO.
The researchers note that this study can be used to predict the monsoon rainfall over the northeast region on a decadal time scale using Pacific Ocean region data.
Previous studies have found that a dry spell may be preceded by a wet spell, so the researchers warn that “change in land cover and deforestation could potentially result in more natural disasters, for example, flash flood, landslides from torrential rains, and damage to crops and biodiversity”.
Policymakers should take these long-term predictions into account while planning construction of dams, power plants, etc. to prevent loss of property.
Mango showers is a colloquial term to describe the occurrence of pre-monsoon rainfall. They are notable across much of South and Southeast Asia, including India, and Cambodia.
These rains normally occur from March to April, although their arrival is often difficult to predict. Their intensity can range from light showers to heavy and persistent thunderstorms.
In India, the mango showers occurs as the result of thunderstorm development over the Bay of Bengal. They are also known as ‘Kaal Baishali’ in Bengal, as Bordoisila in Assam and as Cherry Blossom shower or Coffee Shower in Kerala.
Towards the close of the summer season, pre-monsoon showers are common, especially in Kerala, Karnataka and parts of Tamil Nadu in India. They help in the early ripening of mangoes, hence the name.
28-Mar-2019: World’s longest salt cave discovered in Israel
An international expedition has successfully mapped the Malham salt cave in the Dead Sea’s Mount Sedom which, at 10 kilometers long, now bears the title of world’s longest salt cave.
Following the biblical recounting of Lot’s Wife who was turned into a pillar of salt, Israel’s Dead Sea region is now famous for a second salt phenomenon: Malham Cave, the world’s longest salt cave.
For thirteen years, this title was held by Iran's Cave of the Three Nudes (3N) on Qeshm Island. Now, an international expedition led by the Hebrew University of Jerusalem (HU)’s Cave Research Center (CRC), Israel Cave Explorers Club, and Bulgaria’s Sofia Speleo Club, along with 80 cavers from nine countries, has successfully mapped the Malham salt cave in the Dead Sea’s Mount Sedom which, at 10 kilometers long, now bears the title of world’s longest salt cave.
Salt caves are living things, geologically speaking. They form mostly in desert regions with salt outcrops, such as Chile’s Atacama Desert, Iran’s Qeshm Island and Israel’s Dead Sea. What helps them form is water—even arid climates see the occasional rainstorm. When it does rain, water rushes down cracks in the surface, dissolving salt and creating semi-horizontal channels along the way. After all the rainwater drains out, these dried out “river beds” remain and salt caves are formed.
Fitting this description is Israel’s Mount Sedom, an 11km long mountain that sits 170 meters below sea level at the southwestern tip of the Dead Sea. Underneath a thin layer of cap rock, this mountain is made entirely of salt. Two factors protect this mountain from dissolving away: the sturdy cap rock that covers its salt, and the arid climate of the Negev Desert. Mount Sedom gets roughly 50mm of rain a year, mostly in short but dramatic rain bursts. The Malham Salt Cave is a river cave. Water from a surface stream flowed underground and dissolved the salt, creating caves – a process that is still going on when there is strong rain over Mount Sedom about once a year. In this way, the Malham Salt Cave is “alive” and continues to grow.
By comparison, Iran’s Qeshm Island salt cave, now the world’s second largest salt cave, measures only 6,580 meters. In addition to its length, the Malham Cave contains a stunning array of salt stalactites and salt crystals within its chambers. These salt icicles hang from the cave’s ceiling and grow longer and fatter as each drop of water rolls down before evaporating into the salty air.
Currently, the survey team is processing final data from the new Malham Cave surveys to create an electronic map of the cave and to publish its findings.