Dear All

As you may be aware there is currently a discussion going on with the aim of identifying unsolved scientific problems in hydrology (UPH).

To make tangible progress, the UPH should:

(1) ideally relate to observed phenomena and why they happen;
(2) they should be universal (i.e. not only apply to one catchment or region); and
(3) they should be specific (so there is hope they can be solved).

One example of an UPH is: "Why is root zone storage related to dry spell duration?"

For details see the IAHS YouTube channel:

https://www.youtube.com/watch?v=jyObwmNr7Ko&feature=youtu.be

We welcome any ideas and invite you to contribute to the discussion on the UPH LinkedIn group:  https://www.linkedin.com/groups/13552921

Alternatively, if you prefer not to join LinkedIn, please email one UPH to Günter Blöschl with a brief justification. The UPH will then be included in the compilation to be discussed on 13 and 14 April in Vienna (Meeting Schedule).
 
Below the list of UPH that have been discussed so far on the group.

Best wishes and looking forward to receiving your UPH.

Günter Blöschl
IAHS President

FLOODS AND DROUGHTS

Do we understand scour and erosion processes occurring during extreme floods?
Can we improve the estimation of extreme flood peak discharges?
How can we evaluate the performance of Flood Early Warning Systems, in terms of losses avoided as a result of a warning?
How do we improve drought (or flood) risk assessments?
How to use nature-based solutions to reduce flood risk and drought risks and increase the resilience of water resources?
How do droughts and floods shape hydrological risk awareness?
How are changes in vulnerability influencing trends in flood risk?
How to assess water scarcity by considering both water quantity and quality Do flood rich-poor periods exist? If so why?
Where and when do flood wave superpositions occur and what are the atmospheric, catchment and river network controls on this process?
Water scarcity assessment

SNOW AND ICE

How can we ensure that improved snowmelt models translate into improved capabilities to simulate streamflow from snowy watersheds?
How can small-scale variability of snow distribution be better represented in larger scale models, and what level of detail is needed for snowmelt runoffmodelling?
Under what conditions is snow melt a more efficient generator of streamflow and groundwater recharge than rainfall?
What is the effect of preferential deposition and lateral redistribution of snow on runoff generation in alpineheadwatersheds?
How to determine the snow water equivalent in mountain regions?

WATER QUALITY

Can we devise a combined eco-hydrology index of river health to balance human and ecological needs?
What is the role of water quality in the water-energy-food nexus?
How to describe human-water interactions in water quality models?
How do we identify the dominant process controlling water quality over different spatial scales?
What controls long-term spatio-temporal evolution of catchment water quality?

EVAPORATION AND PRECIPITATION

Soil evaporation and soil evaporation/transpiration partition How plants and grass works and interact with soil and atmosphere to produce evaporation?

SCALE AND SCALING

Will we ever find the best approach to extrapolate point scale data to the catchment scale?
Combining understanding gained at different spatial scales, e.g. generalizing lessons learned from case studies to larger scales.
How dominant hydrological processes emerge and disappear across the scales.
Can we trade space for time in hydrology?

MODELLING (GENERAL)

Can hydrological processes of highly urbanized watershed be realistically simulated/predicted?
What future for process based modelling beyond persistent dilettantism ?
How to solve the energy budget, the carbon budget and the sediment budget together to constrain hydrologic models results?
Which new mathematics to choose for the hydrology of this century?
Does machine learning have a real role in hydrological modelling
How can we really cope hydrological modeling with remote sensing measures ?
When will hydrological models (HMs) be robust enough to anticipate accurately future water conditions?
Is it possible to remove the independence condition in the multivariate frequency analysis (e.g., when using Copulas)?
What is the value of soil moisture observations for hydrologic predictions?
How can we identify the independent factors determining a nonlinearly evolving hydrologic response?
How can one identify the optimal sample dimension to use in multivariate analysis with copula functions?
Assessing the impact of non-stationary (epistemic) precipitation errors on hydrological model predictions

LANDSCAPE PROCESSES AND STREAMFLOW

Why we can not predict river runoff?
Why are the distribution of distances from a point in the catchment to the nearest river reach exponentially distributed?
Why / How does hydro-geomorphology follow thermodynamic laws - Coevolution, structure-function, emergence, anisotropy, scaling...
How can we explain the ubiquitous existence of patterns in hydrology providing constraints on heterogeneity and preferential flow of water through media Natural heterogeneity, thermodynamics and (yet again) closing the waterbalance
What controls the long term water balance, apart from aridity?

MEASUREMENTS AND DATA

Is it possible to accurately measure flow discharge using gauge-cams (or UAV-mounted cameras)?
A large number of inaccurate observations vs a few accurate measurements: what is our best choice?
Working with different data sources (and there varying spatial and temporal resolution), for example impact & vulnerability information, citizen science data, satellite data.
How can we accurately measure water fluxes in the subsurface (soil and groundwater) at a range of scales?
How can we detect and measure spatial hydrological patterns?
How to cost- efficiently observe multiple tracers at a high temporal frequency at various locations?

GROUNDWATER AND SOILS

Can we better account for the complex water flow dynamics in the vadosezone?
What controls the distribution and depth of actively circulating water in the subsurface?
It is time to change our mind to augmenting groundwater recharge by focus on water-bearing formation in uplands watershed not just in flood plains or alluvial fans!
What controls the source of water to wells?
Where and why is the largest global store of freshwater (groundwater) connected to other parts of the hydrologic cycle?
Why transport modeling in the subsurface is often inaccurate and fraught of uncertainty?
What are the main processes controlling transport and transformation of contaminants across scales?
Why assessing groundwater resources and their variation is space and time is a daunting, though dramatically needed, endeavour?
Why removal of contaminant from groundwater by pump-and-treat does not work?
Closing the mass-age balance by measurement

HYDROLOGICAL CHANGE

Why are some catchments more sensitive to land-use/cover change than others?
Is the hydrological cycle regionally accelerating under global warming?
Influence of climate variability on large rivers runoff
Dealing with non-stationarities, e.g differences in timescales between analysis tools & methods, modeling of non-stationary processes
Quantifying the human influence on hydrology and hydrological extremes at the catchment scale What is the real impact of man on the water volumes transferred to the sea by rivers?
Why are springs in mountains drying up?
How can we detect and attribute change in flood characteristics?
Sudden and abrupt changes of water management conditions?
Why do we see long term cycles in temperature, rainfall and river flows?

ASSORTED

Elementary physics of hydrological cycle.
Impact of solar activity on hydrological cycle of the Himalayan and Indian Peninsula Rivers.
Does hydrology needs non-equilibrium thermodynamics or even a new type of thermodynamics ?
How we can do hydrology science more open and replicable?
How can we link our hydrological science with stakeholders?