Delayed monsoon onset in Central India: early warning forecast
13 May 2020 | Source: Potsdam-Institut für Klimafolgenforschung
Summer Monsoon in Central India will likely begin between 18th and 26 of June, according to the new early forecast developed at the Potsdam Institute for Climate Impact Research (PIK). Led by PIK expert Elena Surovyatkina, the Monsoon forecast method showed to be successful already four years in a row. With global warming the monsoon is changing, breaking well-established “rules” of the phenomenon and thus becoming more unpredictable. A raising demand for a new understanding of the Indian Monsoon in order to be better prepared makes long-term forecasting even more important.
“2020 is an unusual year, due to pre-monsoonal showers in many places. Specifically, the rainfall in North-Eastern India and Eastern part of Central India impacts on upcoming monsoon. While it is good to have rain in sweltering spring, unfortunately, the pre-monsoon rainfalls usually disturb the formation of impending well-organized monsoon, delaying and weakening the monsoon", Elena Surovyatkina explains. “Moreover, there is an essential condition for monsoon onset: Before monsoon onset, the daily temperature in the Eastern Ghats is decreasing, while in North Pakistan it is increasing - at monsoon onset, the temperatures will match. Compared to the average of the last five years, the daily average temperature in the Eastern Ghats in April is about 1° lower, but in North Pakistan it is about 4°C lower than the 5-year average. Hence, it takes several days for the temperature in the Eastern Ghats to drop-down to meet the North Pakistan level, this notably delays the time of monsoon onset".
New method forecasting regional monsoon rainfall amount
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 the Bay of Bengal. "When both branches are strong, the whole Indian subcontinent receives a good amount of rainfall", Surovyatkina highlights. "However, in the last years the branch from the Arabian Sea has become stronger. This tendency remains for Monsoon 2020 and could mean a One-Handed Monsoon again: The western coast of India could receive a lot of rainfall from the Arabian Sea branch, while the eastern coast might face a deficit of rain”. And that, of course, raises the question of how much of a rainfall deficit.
That’s why Surovyatkina’s Monsoon Research Group extended the scope of expertise this year by developing a new methodology for forecasting the regional amount of monsoon rainfall. "Here, we present our first test for the upcoming monsoon and the period from June to September,” explains PIK researcher Jingfang Fan: "According to our estimations, the forecast for the monsoon 2020 is the following: for All India 842.85 mm (-5% below average), for Central India - 854.07 mm (-12%), for East & Northeast India - 1245.54 mm (-13%).” Compared to the usual rate, these results indicate an overall deficit of the monsoon rainfall. This might be explained by the conditions of the oncoming El Nino, which PIK scientist Josef Ludescher expects with 80 percent likelihood by the end of 2020.
While the western coast of India might face heavy rainfall and floods, the eastern coast might have to save water. Thus, sharing water is a challenge of upcoming Monsoon 2020, the scientists conclude.