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Changing Seasonality of Annual Maximum Floods over the Conterminous US
  • Bidroha Basu,
  • Rajarshi Das Bhowmik,
  • Sankarasubramanian Arumugam
Bidroha Basu
University College Dublin
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Rajarshi Das Bhowmik
Indian Institute of Science
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Sankarasubramanian Arumugam
North Carolina State University

Corresponding Author:sankar_arumugam@ncsu.edu

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Understanding the flood generating mechanisms that influence flood seasonality in a region provides information on setting up relevant contingency measures. While former studies had estimated flood seasonality at regional/continental scale, limited/no studies had investigated the climate/basin drivers that influence the changes in flood seasonality. Considering this, the current study performed two analysis i) estimated the changes in the seasonality of annual maximum floods (AMF) between pre- and post-1970 across Hydroclimate Data Network basins over the coterminous United States, and ii) identified the predictors that influence the change in the seasonality from a set of climate and geomorphic variables. Significant changes in the AMF seasonality were noted for approximately half of the basins in the eastern US while low to no change was found in a majority of the basins in the central/western US. We found that a decrease (increase) in the seasonality index, indicating floods arriving more uniformly (more concentrated in time), is typically associated with an increase in the precipitation (temperature) in basins where a strong change in flood seasonality occurs. Elevation has a more dominant role as compared to the drainage area in changing the flood seasonality as the former affects the form of precipitation in basins in higher elevations. This is particularly true for western US where floods arrive more distributed over the year (i.e., decrease in flood seasonality index), which potentially indicates increased warming resulting in early snowmelt.