2002 Annual

Tuesday, 15 January 2002: 5:00 PM
Influence of hydrologic memory on terrestrial impacts of ENSO
Praveen Kumar, Univ. of Illinois, Urbana, IL; and J. Chen
Poster PDF (2.3 MB)
Relationships among the terrestrial hydrologic processes over the North American continent associated with the El Niņo/Southern Oscillation (ENSO) are investigated using a large area basin-scale land surface model driven by European Centre for Medium-Range Weather Forecasts Re-Analyses 15-year (1979-1993) dataset. The cross-correlation coefficients between terrestrial variables and the ENSO index are computed.

We find that the runoff from northern part of North America is most often negatively correlated with ENSO, and there are four distinct significant regions over the continent where the runoff anomalies are positively-correlated. The terrestrial systems have a delayed response to the ENSO signals, as compared to the precipitation, where the delay may range from a month to a season or longer. The shorter and longer delays are typically associated with rainfall runoff, and snow accumulation and melt processes, respectively. The soil moisture storage plays a very vital role in delaying the effects of the climate variability on the terrestrial hydrologic processes and in extending the influences of the El Niņo or La Niņa events on the terrestrial climate.

It is also found that the fluctuations of the soil temperature anomalies at different soil depths, in certain geographic regions, are correlated with the ENSO signal, and the strength and the associated time lag of this correlation increase with increasing soil depth. This reflects that the signature of the ENSO signal on soil temperature propagates down into deep soil due to the low frequency variation of ENSO. We found that the anomaly of the terrestrial heat storage, consisting of heat stored in the soil moisture and soil particles, above the water table is controlled by the fluctuations of the heat stored in the soil moisture. The anomaly below the water table is primarily controlled by the fluctuations of the soil temperature. The ENSO correlation pattern with the anomaly of the terrestrial heat storage over North America is similar to that of soil moisture storage.

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