The project has advanced understanding and modeling of hydroclimate variability over the Great Plains of the United States during the agriculturally important summer season. Societal interest in regional hydroclimate (rainfall, soil moisture, surface temperature, streamflow, drought indices) is intense and growing for it impacts personal well-being as well as the agriculture and food security of the nation.

The seasonal rhythms forced by the annual march of the Sun are predictable but hydroclimate evolution seldom follows the climatological track: Departures from the seasonal-cycle, or anomalies, are of key interest from the societal impact and climate prediction perspectives. The project thus focused on the structure and causes of summer hydroclimate anomalies over the US Great Plains – a major granary of our planet. This region is however prone to both long-term and short-term droughts, e.g., the decade-long Dust Bowl drought of the 1930s and the short drought of 1988; a severe drought is developing this summer as well.

Prior to the initiation of project research, summer rainfall anomalies over the Great Plains were thought to result more from the local moisture sources than the remote ones; this assessment had been reached from modeling studies of land-atmosphere interaction. Observationally-rooted project analysis however showed these rainfall anomalies to be generated in good measure by moisture transports from the Gulf of Mexico through anomalous strengthening/weakening of the Great Plains Low Level Jet (concentrated northward flow from the Gulf of Mexico towards the continental interior at a height of approximately 1Km carrying copious amounts of moisture). The jet fluctuations were moreover shown to be connected to sea surface temperature (SST) variations in the Pacific and Atlantic basins, especially the latter; laying the foundation for the observation-based reconstruction of the notable droughts of the 20^th century.

The project analysis showed the Atlantic SSTs to be especially influential in forcing multi-year droughts; often, more than the Pacific ones. Atlantic Multidecadal Variability, in particular, contributed substantially to two of the four reconstructed episodes. More importantly, the SST influence on droughts was shown to be more extensive and significant in nature than in current climate models; the Atlantic’s influence, in particular, was found significantly underrepresented in the present-day models. 

The project findings are encouraging for the initiation of experimental prediction of multi-year droughts (and wet-spells) over the Great Plains from observationally-rooted statistical models. They also indicate that the widely referenced La Nina–US Drought paradigm is of limited relevance for the multi-year warm-season droughts over North America.

Last Modified: 08/12/2012
Modified by: Sumant Nigam