This PEST TestCase uses 2 observations from a summary file, which differs from others that use observations from a time series.

The TestCase weather and DEM data are for Washington, DC. 

The TestCase goal is to find values for Discharge_Subsurface_Initial_mph, VadoseZone_Transmissivity_Max_m2ph, StorageDeficit_VadoseZone_m that give the same value for StorageDeficit_VadoseZone that maintain a water balance. 

These parameter values may need to be found just one time for a city when it uses a single dem.asc. But they may need to be found twice if the city is simulated at two different resolutions. This was done in Karlsruhe, Germany to ensure the water balance was the same for the 30m and 300m resolution dem.asc inputs. The changing of DEM resolution occurs for a variety of modeling reasons, including to speed up i-Tree Cool Air simulations when coarsening from 30 to 300 m, and this should be done while maintaining the water table depths so the hydrology remains constant despite changing resolution. The i-Tree Hydro model is used to rapidly find parameter values for the i-Tree Cool Air model.

The saved TestCase replaces a 2 year simulation with a 1 day simulation to shorten run times. The 1 day simulation does not achieve the water balance. The 1 month simulation: StartDate_YYYYMMDD = 20181001 and StopDate_YYYYMMDD = 20181101, and again, it is not a water balance. However, the file HydroPlus_PEST_Commands.csv contains the water balance values for the variables being calibrated, set as the initial value. It is not necessary to set those values so specifically to achieve a calibration; it is just a method to save their records. 

The information below is for the 2 year simulation, including the parameter values. 

Resulting values for the 2 water year simulation:
<Discharge_Subsurface_Initial_mph> 3.4328359E-05</Discharge_Subsurface_Initial_mph><!-- Options: > 0; initial stream discharge and soil moisture deficit; units m/h-->
<VadoseZone_Transmissivity_Max_m2ph> 7.3320160E+01</VadoseZone_Transmissivity_Max_m2ph><!-- Defines soil transmissivity when entire soil depth is saturated; units m^2/h-->
<Parameter_m_KsatExpDecay> 3.6145290E-01</Parameter_m_KsatExpDecay><!--Options: >0; Scale parameter for decay of hydraulic conductivity with depth; unitless-->

The observed values were set for TS_first_StorageDeficit_VadoseZone.csv = TS_Last_StorageDeficit_VadoseZone.csv = 2000 mm.
These values were based on what seemed a good balance after running StartDate_YYYYMMDD = 20181001 and StopDate_YYYYMMDD = 20200930, two water years, and observing the StorageDeficit_VadoseZone_m time series in the output file TimeSeries_PerviousVariables_Catchment_m.csv. 
Then a PEST calibration was run with the same StartDate_YYYYMMDD and StopDate_YYYYMMDD, the same water years, to find the values of Discharge_Subsurface_Initial_mph, VadoseZone_Transmissivity_Max_m2ph, and Parameter_m_KsatExpDecay. 


This process could then be repeated for the dem.asc = dem.300m.asc using the previously determined TS_first_StorageDeficit_VadoseZone.csv and TS_Last_StorageDeficit_VadoseZone.csv, and finding the new values of Discharge_Subsurface_Initial_mph, VadoseZone_Transmissivity_Max_m2ph, and Parameter_m_KsatExpDecay.