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    West coast of India may get heavy rainfall; forecasts PIK

    Synopsis

    Indian meteorologists say that the Indian and other global forecast models, which take more factors into consideration, unlike PIK team, which uses a single predictor.

    Koll said that the positive forecast from the global agencies is largely based on the favorable conditions in the Pacific as there is no coherent sign of an El Niño developing during the early stage of the monsoon.
    Dr Elena Survyatkina, a meteorologist working at the Postdam Institute for Climate Impact Research (PIK) has forecast that the 2020 monsoon is likely to be One Handed Monsoon, pouring heavy rains over the west coast while keeping the east coast deficit.

    However, India Meteorological Department (IMD) has forecast a normal monsoon with 100% rainfall and will speak about monsoon's regional distribution in its second forecast to be issued in June.

    PIKs' forecast says: "India is surrounded by the Bay of Bengal on the east and the Arabian Sea on the west. Summer monsoon arrives in two branches: from the Arabian Sea and from the Bay of Bengal. When both branches are strong, the whole Indian subcontinent receives a good amount of rainfall. However, it is a trend in the last years when the Arabian Sea branch is becoming stronger. In Monsoon 2020 this tendency remains, and the One-Handed Monsoon expected to be again. That means that the western coast of India could receive a lot of rainfall from the Arabian Sea branch, but on the eastern coast might be a deficit of rain. And that, of course, raises the question of how much of a rainfall deficit. "

    Indian meteorologists say that the Indian and other global forecast models, which take more factors into consideration, unlike PIK team, which uses a single predictor.

    "As of now, IMD and global agencies unanimously indicate normal monsoon rains for June–September, which is a good news. Unlike the statistical forecast from PIK (which is based on a single predictor), these models are dynamic and takes into consideration other factors that interacts with the monsoon— for example the conditions in the Pacific and the Indian Ocean and so on. The PIK team uses a statistical method for their monsoon predictions. It is based on the temperature difference between central India and north Pakistan, which they use as an indicator of the strength of monsoon. ," said Roxy Mathew Koll.

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    Koll said that the Arabian Sea has been warming rapidly in the recent decades. "As a result, the monsoon branch is exhibiting more fluctuations. So occasionally there are episodes where huge amount of moisture is dumped along the Western Ghats in a few days' time," he said.

    In a 2015 paper published in Nature Communications, Koll and other scientists had observed 'a significant weakening trend in summer rainfall during 1901–2012 over the central-east and northern regions of India, along the Ganges-Brahmaputra-Meghna basins and the Himalayan foothills, where agriculture is still largely rain-fed'.

    Koll said that the positive forecast from the global agencies is largely based on the favorable conditions in the Pacific as there is no coherent sign of an El Niño developing during the early stage of the monsoon. El Niño, if present, can weaken the moisture carrying monsoon winds and reduce the rainfall received.

    However, Koll highlighted that in the absence of the El Nino, Indian ocean is likely to play a dominant role during the monsoon season of 2020, which can yield adverse results over central India. "There is however another signal that we should pay attention to. The ocean temperatures in the equatorial Indian Ocean are forecasted to be warmer than usual during the monsoon time. Our analysis has shown that such conditions can have an adverse impact on monsoon rains over central-north India. The significance of Indian Ocean is increasing year by year as it is warming rapidly due to increasing carbon emissions. Forecast models do not generally pick this link between a warm Indian Ocean and the monsoon rains. Hence in the absence of the El Niño, there is a chance that the Indian Ocean play a dominant role in controlling the monsoon rains."

    He added: "Also, a warm Indian Ocean can spurn off cyclones during the monsoon onset time. This can interfere with the normal progression of the monsoon, and we have seen this happening in the past several years. So we need to keep a watch on the Indian Ocean on how this year's monsoon is going to be."
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