Unsolved problems are a good way to define research programmes in science. One of the most famous set of unsolved problems was the 23 problems the mathematician David Hilbert posed in 1900, that had a big influence on the direction of mathematics in the 20th century.
Hydrologists, noting what had happened in mathematics, decided to try the same thing for their field. In 2017 a call was made out - “To all hydrologists of the world: A Call to Arms! What are the 23 Unsolved Problems in Hydrology that would revolutionise research in the 21st century?”.
As a result, 230 hydrologists came together to put together a list of 23 unsolved problems. (Here’s my previous article on this effort).
However one of the reactions to this list, was that the problems, while important, were not exactly bold and daring. One paper, reflecting on these unsolved problems and their related hypothesis, wrote “While the notion of hypotheses in hydrology has received renewed interests in recent years, most of them are not outrageous. One of the few examples is the idea of an ‘active biotic pump transporting atmospheric moisture inland from the ocean’”
That being said, I think we can come up with a more interesting set of hydrology problems. There are actually a lot of exciting problems related to water that the mainstream hydrologists missed. One has to think a little outside the box a bit, and see how water connects to other aspects of the earth system. I actually think hydrology is one of the most exhilirating fields in science right now. It has the potential to see an explosive growth just like neural science or microbiome biology has seen in recent decades. Hydrology has the potential to rewrite the way we understand climate science, global warming, ecology and evolution. It plays a key role in understanding earth as Gaia.
Here’s a proposal for a list of more important and exciting unsolved problems of hydrology:
How much does groundwater levels reduce wildfire risk? (Tree roots bring up groundwater in dry season, which can hydrate landscape and also create rain)
How much does groundwater levels affect rainfall? Especially in dry season when tree roots bring up a lot more groundwater.
Is the drought-fire-flood feedback loop real? Is it leading the world to desertification? How will restoring the water cycle get us out of the drought-fire-flood feedback loop
Is there a phase transition in climate behavior due to water cycle shifts, as we switch from industrial farming to regenerative agriculture practices? If there is can we get a ball park percentage number for the shift
Are microbes and fungi regulating the global temperature via the water cycle? via regulating transpiration and cloud formation, meriodonal transport, greenhouse gas
Are microbes and fungi regulating droughts and storms via the water cycle? If so how much, and what is the mechanisms?
How much is the pharmaceutical system with its products that disrupt the microbiome, disrupting the global functioning of the water system, and its connected climate impacts?
Were ice ages caused by a disruption of the water cycle and its connection with the ecosystem?
If water cycle and ecology co-evolve, how much does this rewrite the theory of natural selection? Is the co-evolution of the water cycle and ecology based on a mix of natural selection and nonequilibrium thermodynamics (using theorems like the Maximum Power Production)?
Is there an optimal speed of cycling for the water cycle?
How much has the speeding of water off the land led to increased fire?
Can the earth’s water system continuing functioning in a healthy manner with the future exponential growth of AI?
How much do we need to slow water (i.e. slowing the runoff of water into the ocean after rains)? What percentage of water needs to be slowed? Is there a tipping point of slowing down where the carbon and water cycles sync up better?
What is the optimal vegetation coverage of the earth, for best functioning of the water cycle?
How much is land-use change causing climate whiplash via its affect on the water cycle?
Does an ecosystem evolve the small and large water cycles for its own needs? Does an ecosystem’s niche construction involve changing the large scale transport of water around the globe?
How much is the damming of our rivers with large reservoirs hindering the global water circulatory system and how it supports earth system functioning?
Is there a global hormonal-like system, and a global brain-like functioning system, involving trophic levels and the earth microbiome, that forms an iterative, networked, self-organizing structure that is self-regulating the earth’s water circulatory system?
There have been interesting microscopic water discoveries like the EZ water (of Gerald Pollack), vortex structures (of Victor Schaumberger), and the stable water clusters (of Shui-Yin Lo). How do these microscopic water structures influence the nucleating of rain? Are these structures carrying information that gets distributed around the global water cycle?
Some these questions have a relation to the Water Ecology Principles I discussed a couple of articles ago. I’ve also previously made a list of key papers in the water & climate field .
Do you have interesting problems to add to the list?
Heres the original 23 unsolved problems the hydrologists came up with in 2017
Time variability and change
1. Is the hydrological cycle regionally accelerating/decelerating under climate and environmental change, and are there tipping points (irreversible changes)?
2. How will cold region runoff and groundwater change in a warmer climate (e.g. with glacier melt and permafrost thaw)?
3. What are the mechanisms by which climate change and water use alter ephemeral rivers and groundwater in (semi-) arid regions?
4. What are the impacts of land cover change and soil disturbances on water and energy fluxes at the land surface, and on the resulting groundwater recharge?
Space variability and scaling
5. What causes spatial heterogeneity and homogeneity in runoff, evaporation, subsurface water and material fluxes (carbon and other nutrients, sediments), and in their sensitivity to their controls (e.g. snow fall regime, aridity, reaction coefficients)?
6. What are the hydrologic laws at the catchment scale and how do they change with scale?
7. Why is most flow preferential across multiple scales and how does such behaviour co-evolve with the critical zone?
8. Why do streams respond so quickly to precipitation inputs when storm flow is so old, and what is the transit time distribution of water in the terrestrial water cycle?
Variability of extremes
9. How do flood-rich and drought-rich periods arise, are they changing, and if so why?
10. Why are runoff extremes in some catchments more sensitive to land-use/cover and geomorphic change than in others?
11. Why, how and when do rain-on-snow events produce exceptional runoff?
Interfaces in hydrology
12. What are the processes that control hillslope–riparian–stream–groundwater interactions and when do the compartments connect?
13. What are the processes controlling the fluxes of groundwater across boundaries (e.g. groundwater recharge, inter-catchment fluxes and discharge to oceans)?
14. What factors contribute to the long-term persistence of sources responsible for the degradation of water quality?
15. What are the extent, fate and impact of contaminants of emerging concern and how are microbial pathogens removed or inactivated in the subsurface?
Measurements and data
16. How can we use innovative technologies to measure surface and subsurface properties, states and fluxes at a range of spatial and temporal scales?
17. What is the relative value of traditional hydrological observations vs soft data (qualitative observations from lay persons, data mining etc.), and under what conditions can we substitute space for time?
18. How can we extract information from available data on human and water systems in order to inform the building process of socio-hydrological models and conceptualisations?
Modelling methods
19. How can hydrological models be adapted to be able to extrapolate to changing conditions, including changing vegetation dynamics?
20. How can we disentangle and reduce model structural/parameter/input uncertainty in hydrological prediction?
Interfaces with society
21. How can the (un)certainty in hydrological predictions be communicated to decision makers and the general public?
22. What are the synergies and tradeoffs between societal goals related to water management (e.g. water–environment–energy–food–health)?
23. What is the role of water in migration, urbanisation and the dynamics of human civilisations, and what are the implications for contemporary water management?
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What a trove of a list, thanks for putting it together - I find something completely mind-blowing about water about once every three months, and I see at least two more here.
I think learning how to apply the Two water worlds paradox (Brookes et al 2010 Two water worlds paradox trees and streams return different water pools to the hydrosphere, paper also findable as Ecohydrologic separation of water between trees and streams in a Mediterranean climate DOI: 10.1038/NGEO722). About different water isotopes forming semi-distinct volumes in soil I think as discrete micro pockets. Several mind blowing possibilities, and truly a strange feeling to read the paper and then go for a walk in a flooding rainstorm and just ponder.
Something I've been trying to find out is - do freshwater mussels fractionate water? as if they do some really interesting things are possible with pollution control and also working with water fractions in general.
These are awesome! As someone lacking experience and knowledge in the area, it’s easy enough for me to understand and still be really meaningful.