This year, due to huge temperature anomalies seen during the pre-monsoon season, there is a serious threat to the Indian monsoon unless the present weather trends restores to the normal.
During the current year April and May, which are the typical Pre-monsoon months in Northwest India and adjoining Pakistan, 5-7 western disturbances have affected the region, disturbing the normal temperature pattern considerably. Actually for the monsoon to arrive in time and give normal rainfall, the preceding months should be dry and very hot. Whereas both these months have recorded more than double the relative humidity usually observed, double the rainfall and 5-10 C below normal temperatures for weeks together.
For instance, we take the example of Lahore that rarely receives any rainfall in May and the dust storm / month average is highest in May. Lahore has a long time average of 5-6 dust storms each May. Thunderstorms with rain, however, are few and far between. Whereas the actual status is that up till now ie, last decade of May, only one dust storm and 3-4 major thunderstorm accompanied with light to moderate rainfall have been observed which is quite contrary to the normal pattern.
This weather pattern has continued into North-West India starting from Amritsar and has affected places like Allahabad -deep into North Central India.
It is to be noted that when very high temperatures are cutoff for a significant period of time, the required low pressure to steer the monsoon winds towards India from the Bay of Bengal and the Indian ocean is not achieved; consequently affecting the onset and rainfall of monsoon.
This is what precisely happened thirty years back in 1987. The pre monsoon months in that year were much cooler than normal and the resultant monsoon rainfall failed miserably. It is important to note that a huge population of 1.5 Billion that includes countries like India, Pakistan and Bangladesh depends on the optimum level of monsoon rainfall. Rice, especially in Bangladesh, where it is the staple food, is seriously affected by failure of monsoon rains and famine usually follows.
So, in short, if the normal temperature pattern is not set in the Indo Gangtic plains and the upper and lower Indus plains of Pakistan in time to produce sufficient low pressure than there are high chances of lower than normal rainfall during the current monsoon season which may affect the lives of billions.