If Rain Falls in India and No One Reports It, Are Historical Trends in Monsoon Extremes Biased?

Abstract

With two thirds of the total Indian population employed by the agriculture sector, changes in Indian monsoon precipitation have widespread implications for human welfare. Increased extreme precipitation since 1950 has been widely reported for central India. Major studies have relied upon the gridded daily precipitation observations provided by the India Meteorological Department (IMD), which assimilate observations from a variable network of weather stations. Replicating the IMD's interpolation method on satellite-based precipitation observations, however, indicates that temporal changes in the observing weather station network introduce a jump in the record toward more extreme rainfall after 1975. Trends evaluated across this jump are suspect, and trends evaluated subsequent to it are insignificant (p > 0.1). This positive bias may also mask declines in average monsoon rainfall. Greater accuracy in these trends may resolve distinctions between climate model simulations of future changes. Access to the underlying data from IMD rain-gauges would facilitate improved rainfall reconstruction.