🌿 Wetlands estimated with irrigated paddy experiment

[mikhailsmilovic]

Hydrological models, CWatM included, often over-estimate discharge at the outlet of basins with significant wetlands.
Eventually, Wetlands will probably be a separate land class or category of land class in CWatM.
Until then, it may be interesting to experiment using the irrigated land paddy class.
This would allow both for evaporation from "flooded fields" as well as transpiration from plants.

This could be done in two steps:

1. Update the paddy fraction land cover to include wetland areas

To simplify the experiment, do not add extra paddy on cells that already have paddy irrigation.
It is possible to specify static paddy and non-paddy irrigation land covers,
In the settings file, in the [LANDCOVER] section:

• paddyfraction = path to map
• nonpaddyfraction = path to map

In this case, forest, water, and sealed (grasslands are determined as the remaining, non-specified land) continue to be determined from:

• fractionLandcover = path to map with all land cover fractions

If all the land covers are static, then the irrigated paddy land class is pointed to at in the normal way as follows:

• dynamicLandcover = False
• forest_fracVegCover = path to map
• irrPaddy_fracVegCover = path to map
• irrNonPaddy_fracVegCover = path to map
• sealed_fracVegCover = path to map
• water_fracVegCover = path to map

2. Create gwAbstractionFraction_Irrigation map to supress groundwater pumping over paddy "wetlands"

CWatM will think the newly added wetland/paddy is irrigated land and then attempt to irrigate it. This is fine with surface water, as the fields should stay flooded. However, for this experiment stage, let us suppress groundwater irrigation. Let us assume for this experiment that limitAbstraction = True.

Assuming sectorSourceAbstractionFractions = True (standard), CWatM will attempt to satisfy demands up to the fraction of demand indicated in the various AbstractionFraction variables. For example, gwAbstractionFraction_Irrigation = 0.5 implies that 50% of the total water demand would be attempted to be satisfied from groundwater, assuming the demand had not yet been satisfied by channels, lift areas, lakes, or reservoirs. gwAbstractionFraction_Irrigation can point to a number or a map.

We are to create a map that has the standard gwAbstractionFraction_Irrigation value everywhere (for example, 1) except in the areas where we've added wetlands -- on all cells with wetlands, we set the value to 0.

• gwAbstractionFraction_Irrigation = path to map with 0s over wetlands and 1s (or recommended value) elsewhere

This will generally confuse the outputs for abstraction, withdrawal, and consumption related to paddy, as it will mix the water use over irrigated paddy land and wetlands. However, if this experiment proves useful, we can create partitioned outputs and eventually the wetland land class.