Identifying the relationship of a satellite derived surface wetness with precipitation and river discharge

There is clear need to observe the surface wetness throughout the globe, and in situ observations are too sparse to give the needed information. The primary goal of this study is to understand how a satellite derived surface wetness index corresponds to cumulated precipitation and melting snowcover. The observations for the wetness index are derived from the relationship between microwave channel measurements provided by the Special Sensor Microwave Imager (SSMI). We will identify the utility and limitation of the index over various areas of the world and under very different climates and vegetation and soil types. The areas analyzed correspond with important agricultural regions in central China, the southeastern U. S., the western Sahel, southeastern Australia, central France, and northern Argentina. Anomalies from the Global Precipitation Climate Program (GPCP) and the wetness index are derived from the 1992-1997 base period. These monthly anomalies are plotted as time series for each of the above study regions. The statistical relationship between the two data sets is also calculated. The wetness index anomalies are allowed to lag the precipitation anomalies, with the understanding that they may retain memory of the precipitation accumulated over the previous months. The statistical relationship between concurrent correlations and accumulative lagged correlation will answer this question. We also analyze the utility of the wetness index to monitor the rate and magnitude of snow melt. The flood over the Red River valley during the spring of 1997 will serve as a case study for this analysis. Ancillary surface data for precipitation, snow depth, maximum and minimum surface temperature and river stream flow levels will serve as validation for the study. Quantitative correspondence between this validation data and wetness values will determine the utility of the wetness index in forecasting the rate of melt water flows through the river channel.