Trends and Multi-decadal Variability in the Hydroclimate of Northern India and Tibet as Manifested in Paleoclimate, Precipitation and Reanalysis Data 1850-2010.

Abstract:

Beginning with the work of Blanford in 1884, the Tibetan Plateau has been recognized as having a profound impact on the intensity of the Indian Summer Monsoon. However our ability to fully characterize the changing nature of the plateau’s impact on the monsoon has been limited by the lack of observations of the hydroclimate of this remote and data sparse region. The recent availability of atmospheric reanalyses that assimilate only surface pressure data now allows the possibility to extend our knowledge of this relationship back in time. In this presentation, we will make use of the 20th Century Reanalysis from the ECMWF (ERA20C) along with the APHRODITE high-resolution gridded precipitation dataset and an ice core extracted from a high elevation site on the Dasuopu Glacier on Shishapangma, an 8000 meter high peak in Tibet situated just north of the Himalaya, to examine trends and multi-decadal variability in the hydroclimate of Northern India and Tibet since 1850.

In particular we show that over the 20th Century, the ERA20C indicates that there has been a statistically significant decrease in annual mean snowfall over the southern Tibetan Plateau and a concomitant increase in annual mean rainfall over Northern India that extends northwards into the Himalaya. Both of these changes are shown to be associated with the enhanced warming that has occurred over the plateau since the start of the 20th Century. These results are consistent with trends in rainfall and snowfall as recorded in the APHRODITE dataset over the last 50 years. They are also consistent with a long-term trend towards lower snow accumulation in the Dasuopu ice core that began in the middle of the 19th Century. We also use an EOF analysis as well as spatial correlation analysis to examine multi-decadal variability in rainfall and snowfall in the region of interest and the changing nature of the relationship between the two.