Using previous tea backyard data, scientists are piecing collectively the image of local weather change


Famed for its tea, Assam’s tea backyard data are giving scientists a glimpse into previous rainfall modifications in northeast India, affected by scattered and spotty historic rainfall information.

For 12 years, the scientists and college students at Cotton University in Guwahati, Assam, combed by means of handwritten tea backyard data spanning 1920 to 2009, to reconstruct a 90-year day by day rainfall dataset.

The reconstructed dataset goals to fill within the gaps in historic rainfall remark community by the India Meteorological Department and generate a new baseline for rainfall within the northeast. This will assist analyse and handle the impacts and dangers as a result of excessive rainfall, in improved methods.

Using the info mined, they had been capable of establish and spotlight the rising frequency and depth of utmost rainfall in northeast India by means of the previous century, whereas the typical rainfall has decreased.

“The rain comes in short spells; the spells are no longer well distributed in space and time like they used to be 30-40 years ago,” Rahul Mahanta, who led the reconstruction, informed Mongabay-India throughout a go to to the college simply days earlier than the Assam floods disrupted life, in June 2022.

Surrounded by registers from tea gardens with yellowing pages, sprinkled generously with dates and numbers in spindly handwriting, Mahanta narrates the story behind the reconstruction.

Historical rainfall information

“While investigating extremes of rainfall [flood and drought] in northeast India, we observed that continuous rainfall data by the India Meteorological Department was only available for 15 stations for 32 years, starting from 1975. But before 1975, the number of stations with rainfall measurement data in a given year decreased, and stations with continuous measurements are even fewer,” Mahanta mentioned.

“To get a true picture of extremes, we need long-term datasets. So, we set about to reconstruct the historical rainfall database using tea garden records. We collected records from private tea gardens and sourced British-administered IMD data collected from British-owned tea gardens in Assam. By the time we collected the data and digitised them, it was 12 years. We had accessed about 547 stations across tea gardens and other documentary sources such as records kept by Jesuit missionaries, by the time we got done,” added Mahanta, who labored with his college students to maintain the info mining effort going with none funding.

The reconstruction builds on steady rainfall information obtained from 24 India Meteorological Department stations from 1920 to 2010 together with stations in Assam, Manipur, Tripura, Meghalaya, Nagaland, and Arunachal Pradesh at elevations starting from 16 metres to greater than 2,000 metres above sea degree.

The group needed to put up with yellowing, disintegrating pages and deciphered unhealthy handwriting; however that was the least of their worries. “We had to also standardise the data and correct errors which was a time-consuming exercise,” added Mahanta.

Handwritten tea backyard data. Credit: Sahana Ghosh/Mongabay.

“Organised meteorological records were facilitated by the British with the establishment of the IMD in 1875. Institutions such as tea gardens retain archives with handwritten records going back to the late 1870s. Because tea and timber production were the main drivers of the colonial economy, and because most of the cultivable land was allocated for them, tea plantation records make up a significant part of northeast India’s documented heritage. Of almost 750 tea estates in Assam, more than 100 have been in existence for over a century and have daily temperature and rainfall records,” in response to a paper by Rahul Mahanta.

Private diaries, periodicals, and journals, and logbooks of medical and scientific analysis present in missionary hospitals within the area, Jesuit libraries, newspapers, and private diaries are additionally wealthy repositories of temperature and rainfall information.

Analysing the 90-year-long information additionally reveals that the variability in rainfall noticed is a part of some global-scale pure forcings, not anthropogenic. “If there are some [anthropogenic forcings] we need more sophisticated methods to decipher them,” he added.

Currently, Mahanta and his crew are trying on the moist and dry spells utilizing the reconstructed dataset (paper beneath assessment) and have discovered altering patterns within the monsoon season since 1970: the depth of extraordinarily moist spells and the variety of extraordinarily dry spells throughout the monsoon season have each been rising in current a long time, which in flip enhance the chance of each drought and flood within the area.

“Rainfall extremes during the months of the monsoon season can be as important as how much total water is received,” says Mahanta. For instance, this yr throughout crucial crop progress levels, too many days with out rain decreased yields in some districts and led to crop failure in some others, which impacts the area’s agriculture-dependent financial system. “At the same time, short periods of very heavy rainfall like the ones we witnessed in April, May, and June this year, created humanitarian disasters, when massive flooding killed hundreds of people in the state,” he mentioned.

Spotty data

Water sources knowledgeable Manabendra Saharia, who was not related with the info mining effort says that an instantaneous software that might work is making ready new precipitation merchandise that can leverage this hitherto unused supply of historic precipitation information.

“Rainfall varies from one place to another substantially. So, the denser the network of stations, the better your understanding of rainfall patterns over an area. A precipitation product essentially is a collection of data from various gauge stations in a single interoperable format. Since IMD has had limited locations for collecting data in northeast India historically, these tea garden stations act as valuable resources for reconstructing climate history,” Saharia at IIT-Delhi added.

Indian meteorologist BN Goswami, who was additionally main the reconstruction analysis, means that the India Meteorological Department ought to add the 90-year-data day by day information to their repository.

“We need long-term data to understand the rainfall variability. In recent years, the data gathering has improved but long-term data for 100 years in northeast is only available for 12 stations in the region. This is not sufficient because the region has a lot of variabilities. IMD needs to try and improve this availability of long-term data for northeast India across all its observatories and stations,” mentioned Goswami, a former director of the Indian Institute of Tropical Meteorology.



Cherapunji in Meghalaya. Credit: Nazmul Ahmed, CC BY-SA 4.0, through Wikimedia Commons.

“Before the 1950s, IMD had more than 100 rain-gauge sites across northeast India. They were very efficient. Even in Cherrapunji, Meghalaya, they had five rain gauges before 1940. But after 1950 there is a drop in the records,” says Mahanta.

The drop in rainfall data corresponds to conflict, social actions, and disasters such because the Great Assam Earthquake in 1950, the 1962 India-China War, the language motion and Bangladesh Liberation War within the Nineteen Seventies, the Nineteen Eighties Assam foreigner’s motion adopted by different ethnic tensions.

“Cherrapunji has a lot of data gaps which is why it is an outlier. If you miss one year that will completely mess up your understanding of the inter-annual variability of rainfall and extreme events. We should not use Cherrapunji in long-term variability studies because there are large data gaps. Then only we can understand the climatic drivers,” mentioned Goswami in a webinar organised final yr by the India Meteorological Department. He additionally emphasised redefining the wet season in northeast India.

Augmenting climate providers

“Climatological rain is more in April in the northeast than June in central India. So, the rainy season starts in April. Even if we leave out April, we get substantial rain in May compared to June in central India. We have to include May in the rainy season for northeast India. We have to define the rainy season from May to September,” he reiterated to Mongabay-India in an interview. Goswami says bettering modeling abilities can also be essential to augmenting climate forecast providers.

Arup Kumar Sarma who works on water sources within the Brahmaputra river basin utilized a rainwater harvesting system (Sustainable Approach of Rainwater Management and Application) to preserve water in tea gardens primarily based on data collected from tea backyard house owners.

“Waterlogging due to short-duration, high-intensity rainfall is affecting tea gardens in the monsoon. We found that there was no way to let the water pass because there were other cultivation areas or roads. So, we designed a water harvesting system in a way to let the water go into the ground so it addresses the drainage issue and also the drought during the winter season,” Sarma on the Indian Institute of Technology, Guwahati, mentioned.

A tea backyard employee on the Aideobarie Tea Estate in Jorhat in Assam. Credit: Reuters.

“We have a two-chamber system where a part of the water goes underground to recharge the aquifer. The water that remains in the upper chamber [the pond portion] can be supplied for the lean season. We used historical rainfall data from the tea garden to get an idea of the maximum precipitation. We used this data to feed into the hydrological model to understand how much water may accumulate and the rate of flow. This helped us design the chambers of the water harvesting system,” he added.

The India Meteorological Department has a community of 18 local weather reference stations or handbook observatories, 156 day by day handbook rainfall stations, 82 automated climate stations, 146 automated rain stations, and 5 automated agro stations (soil parameters, rain and ambiance) in northeast India. It additionally has higher air observatories with refined instrumentation.

The India Meteorological Department is extending the automated agro stations by one other 18 to get a whole image of the soil moisture at varied depths throughout the area; additionally it is putting in 40 automated climate stations alongside the India border in Arunachal Pradesh, including extra doppler climate radars and getting a knowledge processing server for the reception of meteorological information from IMD’s community and different information from the area.

This article was first revealed on Mongabay.



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