[HubbardBrookCOS] Dear Colleagues Letter on Reducing Precipitation Gauges at HBEF

[Rustad, Lindsey -FS]

Dear Colleagues,
As promised at the September 28, 2016 COS meeting, we are following up on the presentations and discussions on changing the configuration of the HBEF precipitation gauges.

The Forest Service currently maintains 24 rain gauges within the experimental catchments and headquarters. Given budget and staff time constraints, the U.S. Forest Service team at HBEF has been considering scenarios that would reduce precipitation monitoring efforts while maintaining the best hydrologic data possible. This action has not been approached lightly.

In order to accomplish this balance, we conducted a full uncertainty analysis. This analysis calculated past precipitation inputs to the experimental watersheds using thousands of unique precipitation gauge reduction scenarios. This analysis allowed us to objectively assess the information loss due to reducing the number of precipitation gauges. We also used the expert opinions of our technical staff and Forest Service scientists to determine the optimal set of gauges to reduce the cost of precipitation monitoring and considering the other measurements that are made at a gauge sites (e.g., temperature, snow, etc.).

Using the uncertainty analysis and level-of-effort considerations, we have decided that we will reduce the number of rain gauges from 24 to 11 (including HQ).  Rain gauges 1, 2, 4, 6, 9, and 11 will be retained on the south-facing slope, and gauges 14, 17, 19, and 23 will be retained on the north-facing slope. This configuration would produce a total absolute uncertainty (between 1998 and 2014) of 1.1% and 0.86% for the south- and north-facing slopes, respectively. We have analyzed how annual precipitation trends, annual evapotranspiration trends, and bulk atmospheric deposition would have been seen under if HBEF had chosen to monitor only these sites starting at the origination of the experimental forest. The comparison of expert opinion scenario to business as usual scenario for total annual precipitation is given as an example in Figure 1 below.  The results from this analysis suggest that the same scientific conclusions would result. Thus, we are confident that this precipitation reduction will not alter our understanding of the forest ecosystem at HBEF.

We welcome any questions about the analyses and thought process used to come up with this scenario. There are many details that could be shared and we are happy to clarify how we made this decision.

Respectfully,

Lindsey Rustad (for the HBEF Team)



Lindsey Rustad, PhD
Research Ecologist and Team Leader Hubbard Brook Experimental Forest
271 Mast Rd
Durham, NH 03824

Cell 603 397 7406






Figure 1.  Comparison of expert opinion scenario to business as usual scenario.
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