Estimated VWB refers to the projected volume that will be obtained as a benefit after the implementation of a project. The estimation could be calculated pre-project or during the project, as a forward projection. Monitored VWB refers to calculating the benefit of a specific project during its implementation. This measurement involves collecting actual data (e.g., precipitation) of the current year which is being monitored. It also involves gathering empirical data to assess the actual impact of the intervention on water resources.
Both estimated and monitored VWB take into consideration the same methodologies and variables as inputs for VWB calculations. The main difference is the time that is being considered to obtain the VWB and available data for that time period. For example, an estimate could involve 10 years of precipitation averaged over the 10 year period for an annual value, where the monitoring could be calculated from the actual precipitation for that year. Results may differ based on the input year and conditions included in the calculations.
