HEC-MetVue supports editing of data across Zones. This is performed with the Overview of Zonal Adjustment Editor. This editor allows for vertically scaling or setting the values of TIN/Grid points within that zone. The goal may be to correct values within a given region or analyze scenarios with different spatial distribution of values. For example, if a precipitation grid is assumed to poorly estimate data in higher elevations, a high elevation zone may be used to increase those precipitation values.
Adjustments can take the form of Uniform or Normalized adjustments. For Uniform adjustments, the user is setting all cells within that zone to the same value. Alternatively, Normalized adjustments identify the multiplication factor required to increase or decrease the zonal average to the target value. In short, Normalized adjustments maintain the spatial distribution of the gridded values. Additionally, Zonal Adjustments may be performed on temporally averaged (PER-AVER or INST-VAL) or aggregated (PER-CUM) values. For example, if hourly precipitation data is being viewed, the one-day total may be adjusted, and that adjustment will automatically be disaggregated to the individual hours, based on the Uniform vs Normalized settings. When using Uniform adjustments, the one-day total would be disaggregated by dividing by 24 hours, then applying that value to each day. Alternatively, when using Normalized disaggregation, the computed scaling factor is applied to each individual hour, maintaining the temporal precipitation pattern.