We are thankful to H. Van den Dool, A. Barnston, and J. Hoopingarner (CPC, NCEP) for having provided us with the North America surface air temperature data. This work was initiated in 1994 during the visit at LMD of M. Jianwen Liu, who is now at the Beijing Institute of Applied Meteorology. The preparation of this work was performed on daily temperatures and runoff over the United States, a dataset which has been kindly provided to us by D. Lettenmaier.
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