I downloaded hundred years (1901-2002) of annual rainfall data from India Water Portal for north-west Bihar (covering districts of Paschim Champaran, Purbi Champaran, Gopalganj, Muzaffarpur, parts of Sitamarhi, Sheohar and Vaishali) and plotted it to discern trends. What I found was truly shocking. There has been a massive decline in annual rainfall in this part of Bihar in last fifteen years. For example, mean annual rainfall in Muzaffarpur and neighboring areas is 1131.67 mm with a standard deviation of 208.45 mm. Annual precipitation was higher than the one hundred year average in 50 out of 87 years between 1901 and 1987, but not once since then. Annual rainfall has been below the long term average every year since 1988. And the deficit is not small or negligible. In twelve out of these fifteen years, precipitation was more than one standard deviation below the hundred year average. For the hundred and one years for which we have rainfall data, there have been only 17 such years when deficit in rainfall was so high. Twelve of these seventeen deficit years have occurred after 1987. Patterns are similar for other districts I looked at.
The deficit is so severe—mean annual rainfall in 1988-2002 period (862 mm) was 26% (315.93 mm) below the mean annual rainfall in 1901-1987 period (1178 mm)—I am wondering if there is something wrong with the data. Else how can this go unnoticed and unreported? At least, I have not come across anything either from meteorologists or from farmers of Bihar who would have been most severely affected.