Spatial Parameters

Spatially varying model parameters are provided via a CSV file specified in config.yaml under the parameters.spatially_varying_file field. This file contains per-stream physical properties required by Model204 to compute infiltration, percolation, evapotranspiration, snowmelt, and runoff.

Each row represents a single stream link, and column names must match exactly as listed below. The model directly reads these columns, applies unit conversions internally, and uses them in the ODE system.

---

Required CSV Columns

• stream Unique identifier for each stream link.

• next_stream ID of the downstream link (optional to pass it to the runoff model).

• drainage_area_km2 Total drainage area for the link $km²$. (Loaded but not directly used for runoff calculations.)

• length_km Channel length $km$. Converted to meters internally.

• area_sqkm Total hillslope area draining into the link $km²$. Converted to m² internally.

• centroid_lon, centroid_lat Longitude and latitude of the hillslope centroid $degrees$. Used in potential evapotranspiration (HamonPET) calculations.

• hu Depth of the static soil storage tank (Hu) $mm$. Converted to meters internally.

• i2, i3 Infiltration (i2) and percolation (i3) rates $mm/hr$.

• sw, ss Relative soil moisture at wilting point (sw) and at stomatal closure (ss) $unitless$. Used to compute actual evapotranspiration (ETactual).

• n Manning’s roughness coefficient (n_mann) $unitless$, used to calculate surface runoff velocity.

• slope Average hillslope gradient $m/m$.

• res_ss, res_gw Residence time in the subsurface storage (res_ss) and groundwater storage (res_gw) $days$. Converted to minutes (alpha3, alpha4) for use in the ODE solver.

• melt Degree-day snowmelt factor $mm/day/°C$. Internally converted to $m/min/°C$.

• t_thres Temperature threshold for snow accumulation $°C$.

---

Insights from Model Code

• The parameter c1 is a fixed conversion factor (0.001 / 60) used to convert precipitation rates from mm/hr to m/min.

• infil and perco are computed from i2 and i3 respectively after applying the c1 conversion.

• Snow processes depend on melt (degree-day factor) and t_thres (accumulation threshold) parameters. Snowmelt is limited by available snowpack and temperature. When the temperature falls below t_thres, all precipitation is stored as snow. If the temperature exceeds the melting threshold (melt_thr = 0°C), snowmelt occurs at a rate proportional to the temperature (temperature * melt_f).

Importantly, the snowmelt rate is limited by the available snowpack (h_snow), ensuring that melting cannot exceed the existing snow storage.

• Hu defines the static tank’s maximum soil moisture storage. Excess water above this depth is routed to surface runoff unless the ground is frozen.

• Evapotranspiration is computed using HamonPET with lat (and implicitly doy) as inputs, while sw and ss define how soil moisture stress modifies the actual ET (ETactual).

• Residence times res_ss and res_gw control water release rates from gravitational and groundwater storages.

• The file must have all parameters with correct units* to avoid runtime errors.

---

Example Spatial Parameters File

This file is located at data/Stony_Brook/Stony_Brook_spatial_params.csv.

stream,next_stream,drainage_area_km2,length_km,area_sqkm,centroid_lon,centroid_lat,hu,i2,i3,sw,ss,n,slope,res_ss,res_gw,melt,t_thres
420558772,420558773,0.112,0.33,0.112,-74.79066176,40.31169117647059,178,4,1.6,0.11,0.33,0.1,0.02,2,55,3.7,0
420557886,420558773,0.086,0.21,0.086,-74.78842949,40.31451923076923,178,4,1.6,0.11,0.33,0.1,0.02,2,55,3.7,0
420553620,420553417,0.761,1.358,0.761,-74.79696121,40.32966235632185,178,4,1.6,0.11,0.33,0.1,0.02,2,55,3.7,0
420553824,420553417,0.053,0.117,0.053,-74.78989583,40.33020833333335,178,4,1.6,0.11,0.33,0.1,0.02,2,55,3.7,0