Friday, June 10, 2011

Niwot SIPNET soil moisture issues

For awhile we've been noticing that SIPNET, optimized on NEE and ET at Niwot, has been running with very high soil moisture levels. They were so high that we weren't seeing some of the water limitations on GPP that we should expect, given field observations. The slide show below shows how we went about trying to address this issue.

The gist is that by optimizing while holding RdConst and WaterRemovalFrac fixed, SIPNET is able to tightly replicate a decade of Niwot NEE data, while keeping leaf and wood carbon pools fairly stable, other parameters well-behaved, and soilWetness in a realistic range.

During optimizations where they are allowed to vary, SIPNET usually estimated RdConst ~1400 and WaterRemovalFrac ~0.001. Sensitivity testing and empirical studies suggest these two values should be fixed closer to RdConst ~25 and WaterRemovalFrac ~0.15.

Hope this is helpful and let me know if you have comments!