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Showing posts from March, 2017

### Ecosystem modeling: a review on spatial resolution and lateral flow

We all agree that lateral flow is important in hydrology, but why most ecosystem models do not consider lateral flow?

The answer is usually related to spatial resolution. In a large scale or global scale GCM model simulation, the spatial resolution is usually $0.5^{\circ} \times 0.5^{\circ}$. At this resolution, lateral flow is usually negligible compared with vertical fluxes.

However, this procedure usually causes problems in mass balance. First, without lateral flow, freshwater into the ocean cannot be estimated accurately. Second, dissolved nutrients into the oceanic systems cannot be estimated.

So the question is at what resolution do we actually MUST consider lateral flow?

The answer depends on the fluxes you are looking into. For example, if you are looking into water flow, it it more than likely you have to always consider it, especially at regional scale. If you are looking into carbon/nitrogen fluxes, the problem will become slightly complicated.

First, we will need to evalua…

### Surface water hydrology: a reach based approach

In surface watershed hydrology, stream network is usually represented by a number of connected stream segments. Outflow from a upstream is then routed to its downstream as inflow at certain time step.

One of the important parameters to determine how long the outflow will arrive the next segment is defined using the travel time. The manning equation is usually used to calculate the open channel flow velocity and rate.

In a typical surface hydrology model such as SWAT or PRMS, these parameters are either prepared or calculated for the model. However, there may be great uncertainty for high-spatial resolution simulations.

For example, a segment travel time may be far less than one hour and a daily time step simulation cannot accurately capture the peak flow at all.

In some scenarios, we are interested in the spatial distribution of flow rate, flow velocity, and other dissolved components (DOC/DIC) in the stream, therefore, a segment based approach is inappropriate.

An alternative way to …