A COMPARISON OF MAPPED ESTIMATES OF LONG-TERM RUNOFF IN THE NORTHEASTUNITED-STATES

We evaluated the relative accuracy of four methods of producing maps o f long-term runoff for part of the northeast United States: MAN, a man ual procedure that incorporates expert opinion in contour placement; R PRIS, an automated procedure based on water balance considerations: Pn ET-II, a physiologically based model of carbon/water balance in forest s: and MAPSS (Mapped Atmosphere-Plant Soil System), a rule/process-bas ed vegetation distribution/water balance model. Our goal was to confir m the accuracy of the modeling and mapping procedures, and to see if a ny improvements to the models and methods might be suggested. In our a nalyses, we compared contour maps derived from the four methods both q ualitatively (visual inspection) and quantitatively (raster overlay an d uncertainty analysis). The manual and automated (RPRIS) methods gave the best results, our analyses suggest that methods directly integrat ing gaged runoff data (i.e. MAN and RPRIS) provide the best results un der current climatic conditions. For predicting runoff under altered c onditions. e.g. climate change, the existing models studied here (i.e, PnET-II and MAPSS) hold significant promise. (C) 1998 Elsevier Scienc e B.V. All rights reserved.