How to Access and Manipulate the Source Code of the SWAT+ Model? Any Tutorials or Guidelines?

Hi all,

I have a question regarding the relationship between evaporation and groundwater fluctuations. Does evaporation cause groundwater to fall, or does rising groundwater lead to increased evaporation?

By "evaporation," I mean actual evapotranspiration from the land surface, as defined by most evapotranspiration models (e.g., GLEAM, MERRA).

I believe this process can be described using a conceptual model:

Imagine a cup of water with green beans soaking in it, covered by a lid. When the lid is opened, water evaporates, and as the water level decreases, does the evaporation (per unit of time) also decrease? The answer is yes, indicating that groundwater (represented by the cup of water) influences evaporation.

Now, imagine the cup is topped by a sponge (representing the unsaturated zone). If we measure evaporation from the top of the sponge (which should represent actual evapotranspiration at the land surface), the evaporation will still decrease as the water in the cup (groundwater) decreases. However, there should be a time lag because groundwater evaporation reaches the sponge first.

This concept is especially relevant for soils, where soil evaporation is derived from both past groundwater evaporation and past precipitation infiltration. Similarly, for vegetation transpiration, a rising water table would lead to increased water uptake by vegetation, thereby increasing transpiration. Again, a time lag would be expected in this process.

In other words, according to this conceptual model, actual evapotranspiration at the land surface tends to lag behind groundwater evaporation.

With this in mind, is it correct that groundwater recharge analysis should subtract evapotranspiration from precipitation and then calculate recharge per unit of time? In particular, in some common response analyses, recharge is considered as the net of precipitation minus evaporation, and then the groundwater time series is fitted with a gamma function or other response functions. However, doesn't this treatment implicitly assume that higher evaporation leads to lower groundwater levels in the future?

However, shouldn't evaporation be a “sink” rather than a “source” of groundwater? Shouldn't the only components of evapotranspiration that affect recharge be vegetation indicating interception losses and soil interception?

Please let me know your answer.

My research is on the impact of climate change on soil moisture dynamics in forest and grassland areas using the SWAT model. I need someone grounded in this area to mentor me. I am also open to collaborations and coauthoring. I tried using Hydrus-1D but it was a bit complicated and so I want to explore the SWAT model.

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1. length of the river

2.Volume of the water in river channel

3. Historical context

4. Catchment area

5. Direction of flow

6. other characteristics (like perennial or seasonal, depth of the channel etc,)

which is the major criterion?

it is found that there is not universal rule to decide which is main river and which is tributary.

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systematic approach on modelling rainfall and flood frequenc

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