CUAHSI's 25th Anniversary Reflections: A Challenge for Today’s Hydrologic Scientists, by Rick Hooper
Posted Jul 7, 2026
A Challenge for Today’s Hydrologic Scientists
By Rick Hooper
In 2001, the National Science Foundation posed the following question: How could an investment of $100 million dollars advance hydrologic science? That’s $180 million today. The answer was obvious. Increase the pool of money for competitive PI grants. But that wasn’t on offer. Rather, what infrastructure investments are necessary to transform hydrologic science? If the community could decide on that, new sources of funds could be made available. And NSF was willing to fund an entity to organize the community. Thus, CUAHSI was created.
It is an opportune time to revisit this question. How is that possible given the uncertainty surrounding NSF (and just about everything else)? Because after the shake-up that NSF is currently experiencing, there will come a time when NSF will have an opportunity to present a new approach to funding research and research infrastructure. It would be wise to have some ideas in hand of where new funds should be invested. In this article, I’d like to share the lessons I learned during the initial years of CUAHSI’s operation.
The community quickly coalesced around four areas for infrastructure investment:
- Hydrologic Observatories. These were envisioned to be much larger than traditional experimental watersheds to incorporate a wider range of landforms (e.g., valley bottoms and riparian zones as well as hillsides) and enable investigations of land surface/atmosphere interactions. Critically, major capital investment (order of tens of millions of dollars) would allow unprecedented instrumentation in both kinds and density.
- Hydrologic instrumentation Facility. A lending facility for high-end instrumentation that could be used on a campaign basis by university researchers.
- Hydrologic Synthesis Center. Modeled after a similar facility in ecology operated by UCSB, the center would have provided travel grants and support staff for interdisciplinary teams of scientists to hold intensive research meetings to produce papers.
- Hydrologic information Systems. An effort to adapt recent cyberinfrastructure advancements in areas like web services to hydrology for data distribution and discovery.
Of these, only Hydrologic Information Systems proceeded as planned, tapping into cyberinfrastructure funding. These efforts produced the data services that CUAHSI operates today. The other three failed for a variety of reasons, but I’d like to focus on Hydrologic Observatories because this was the largest effort involving the most people.
To land a major infrastructure project, there must be a compelling hypothesis that the infrastructure addresses that will be ‘transformative,’ to use the NSF buzz word. A good example is the Ocean Observing System that was recently in the news for defunding which was under development during this period. The idea was simple New technology allowed the deployment of cabled sensors to provide continuous data in a science that had relied on episodic data from research vessels. Anyone can see how this a different kind of data that could be beneficial. Of course, details of where to place these, how many, etc. are important and had to be worked out. But the idea was easy to grasp.
We repeatedly tried and failed to come up with hypotheses that the community could coalesce around. Essentially, we wanted to characterize a landscape with intensive instrumentation that would allow us to develop hypotheses, but that is a non-starter at NSF. Even if we could proceed on that basis, how to determine what should be done? With no organizing principles, it is impossible to determine.
Why couldn’t we develop the necessary hypotheses? Because the terrestrial hydrologic system is poorly observable. Contrast our study area with the oceans and atmosphere. These are continuous fluids where much of the physics of motion are understood, at least within certain scales. Enough is known to pose hypotheses at the boundary of knowledge than can develop broad community support.
The subsurface is central to understanding the dynamics of terrestrial hydrology but we struggle to observe its hydraulic properties at a scale that is relevant. Progress has been made in some areas of terrestrial hydrology. LIDAR enables precise mapping landforms at high resolution. Satellite data like GRACE may help with groundwater dynamics, but at coarse spatial and temporal scales. Similarly, geophysical data provides some characterization of the subsurface but it provides loose bounds of the properties that we must determine.
That’s the problem. What do we do? A few suggestions. First, think about examples where key observations transformed our process understanding. In my area, Jeff McDonnell and his colleagues did a series of trench studies around the world that highlighted the lack of connectedness between hill slope and valley that challenged the traditional view of the streamflow generation and explained the dynamics of stable isotope concentration during storms that had befuddled hydrologists for decades. The key point is that the trench enabled observation of a new type of water—mobile hillslope water—that had not been seen before. Its dynamics and chemistry could be linked to other properties such as landform and soil moisture to gain new insights. I’m sure there are other examples that will provide inspiration for dreaming up new ideas.
Second, review the results of other major infrastructure projects. NEON is the most relevant. Which of its data products have been most useful? Why? How have various design elements (e.g. siting, frequency, sensor selection) worked out? What has been successful and what can be improved?
In these uncertain times, I encourage you to take a step back and think about what hydrologic science needs to advance.