Enhanced Model Better Assesses Impact Of Climate Variability

The natural unit for the representation of hydrologic processes is a river basin, Kumar said. "By using a large-area, basin-scale model, we can better characterize the variation of moisture distribution between land surface and atmosphere, so we can more effectively study key feedback mechanisms." For their study, Kumar and graduate student Ji Chen combined digital elevation data from the United States Geological Survey along with hydrologic characteristics such as river basin boundaries and drainage networks. Then they added topographic parameters – water table fluctuations and vertical and horizontal ground water transport – to the model. To compare results, they ran the model both with and without these topographic enhancements.

Simulations for the entire North American continent were performed using the International Satellite Land Surface Climatology Project datasets for the years 1987 and 1988. The researchers validated their model by comparing model predictions against streamflow data collected by the USGS on rivers such as the Mississippi, Missouri and Ohio.

"When run with the enhancements, the model captured both the seasonal and the inter-annual variability quite realistically," Kumar said. "For example, seasonal patterns of streamflow in the tributaries of the Mississippi River basin were consistent with the actual measurements. The model also correctly predicted the winter-spring runoff from the Appalachian mountain range."

Because a severe drought occurred in the Midwest during the summer of 1988, the two-year simulation also provided an opportunity to assess the model’s performance for a dry year as well as for a typical year. The model properly portrayed the impact of the drought through decreased streamflow and increased water table depths within the affected region.

"By incorporating topographic influences into the model, predictions of terrestrial water balance and streamflow were improved significantly," Kumar said. "This provides a much better mechanism for assessing the impact of climate fluctuations on terrestrial hydrology, and for studying the potential consequences of environmental problems."

The researchers described their model in the May 1 issue of the Journal of Climate. The National Aeronautics and Space Administration and the National Science Foundation supported this work.