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Showing posts from May, 2020

Why we need a unified mesh for Earth system model

In many of my early posts, I shared some aspects that why I decided to develop the hexagon based watershed model, HexWatershed. But the real motivation lies beyond watershed and I'd like to share some personal motivation why I started this project.
For decades, since human invented computers and hydrologists invented hydrologic models, we rely on computational techniques to simulate hydrologic processes. And these techniques mostly use the structured mesh/matrix to describe the real world. Nearly all of us are familiar with the so-called X-Y-Z 3D domain.
We stand on the shoulder of giants but we seldom question them.  It is true in earlier days that most of our research activities focus on a catchment scale or plot scale. We have to admit this is important because we need to understand the fine-scale process before we can extrapolate to a larger domain.
We never look at hydrology on a global scale using a global method. Most of us are simply trying to copy the watershed scale method t…

Hybrid modeling for Earth system model

Recently I have been thinking about some philosophy in how model the real world.
For many of us working on the Earth system model, we spent great efforts trying to understand the physical world. For example, we now have a reasonably good idea about how water flows within the system.  
Based on our understanding of the physical laws, we built quite a few of process-based models to model and predict different types of systems.
On the other hand, there are also processes that are not "simply" governed by physics. For example, human activities, or some stochastic processes like wildfire. 
For some processes, it would be more beneficial to use agent-based modeling (ABM) approach. For example, how an individual tree interacts with its surrounding environment, fighting for water and nutrients, should be possible to be implemented using the ABM.
Other processes, such as animal behavior models, are also similar to ABM.
The new question is: how can we merge the process-based model, or equat…