Background on Evaporation and Precipitation on Reservoirs

Quantifying Evaporation and Precipitation flow

Evaporation losses and added storage via precipitation are major components of a reservoir's mass balance. Evaporation and precipitation rates are both generally measured in length/time. In metric units this is often mm/day.

To get volumetric daily flow rates which are required for Pywr, these rates are then multiplied by the Area of the reservoir. In the metric templates in WaterStrategy this Area is generally expressed in Km2.

For a template that uses flow in Mm3/day, a conversion of 0.001 is required to obtain Mm3/day.

Evaporation (mm/day) * Area (km) * 0.001 = Mm3/day

For a template that uses flow in Ml/day, no conversion is required to obtain Ml/day.

Evaporation (mm/day) * Area (km) * 1 = Ml/day