Monday, May 18, 2015

Bimodal pore size distribution and hillslope stability

This post is to highlight the work of Fabio Ciervo, a Ph.D. student of Mariolina Papa that I co-advised with Vincente Medina. His thesis had the merit to put together two nice aspects of the recent research on soils. The first came from the work of Nunzio Romano [1] and co-workers, who show consistently that many soils present a bi-modal distribution in porosity, with effects in the form of the soil-water-retention curves (SWRC), and hydraulic conductivity, once Burdine or Mualem's [2] theory is applied. The other is the novel theory of hillslope stability coming out from the joint work of Lu, Likos, and Godt (e.g. [3]).

Who wants to enjoy his thesis can find it here: Fabio Ciervo, Modeling hydrologic response of structured soil, University of Salerno, 2015.
The code, developed in Java, that solves Richards 1D equation using these bimodal SWRC can instead be found on Github.
The Thesis produced a first paper which is under review in Vadose Zone Hydrology Journal.

Some References (others in the Dissertation)

[1] -Romano, N., Nasta, P., Severino, P., and Hopmans, J.W., Using bimodal lognormal function to descrivbe soil hydraulic properties, Soil. Sci. Soc. Am. J.,  75(2), 468-480, 2011

[2] - Roth, K., Soil PhysicsInstitute of Environmental Physics, Heidelberg University,
D-69120 Heidelberg, Germany, 2012

[2] - Lu, N., and Godt, J., Hillslope hydrology and stability, Cambridge University Press, 2013

Friday, May 15, 2015

La teoria dell'idrogramma Istantaneo Unitario

L'idrogramma instantaneo unitario è una teoria semplificata dell'aggregazione e propagazione dei deflussi. Ecco nel seguito, le mie lezioni (per il corso di Costruzioni Idrauliche per Ingegneri Civili a Trento).

 Tuttel le slides insieme: La teoria dell'idrogramma istantaneo unitario e dell'idrogramma istantaneo unitario 

Slides e Audio:

1 - Introduzione allo IUH. Audio 2014 (31.1 MB);  Audio 2015 (19.5 Mb);
2 - Alcune distribuzioni dei tempi di residenza (5.8 Mb); Audio 2015: Alcune distribuzione per tempi di residenza (7.2 Mb).
3 - Idrogramma Istantaneo unitario GeomorfologicoAudio 2014  (16.8 Mb). Audio 2015 (20.3 Mb)
4 - Portate massimeAudio 2014 (17.4 Mb).
5 - L'idrogramma istantaneo unitario basato sulla funzione di ampiezza.

Generazione del deflusso (Runoff Generation)

Questa parte include l'analisi della formazione dei deflussi superficiali e, sebbene da me non amati, vari metodi più o meno empirici per calcolare l'infiltrazione.

1 - La generazione del deflussoAudio 2014 (27.9 Mb). Audio 2015 (36.5 Mb)
2 - Il Topmodel. Audio 2015 (14.8 Mb)
3 - La generazione del deflusso nel modello ARNO/XINJANG
4 - Il modello del Soil Conservation Service

Ecco alcuni modelli semplificati di infiltrazione. Ma perchè usarli, quando si possono usare semplificazioni dell'equazione di Richards (see point 10) ?

5 - The good-old- Horton model of Infiltration
6 -  The Green-Ampt model of infiltration

Altri Vecchi Audio (2014)
 2b-5b - Audio metodi semplificati per il calcolo del deflusso superficiale o dell'infiltrazione (escluso SCS - 23.4 Mb)

Monday, May 11, 2015

Use and Perception of Science's Results

I asked to Bilal Adem Esmail, one of our Ph.D. students, working on the relation existing between ecosystem services and the water cycle to comment my previous post on ecosystems and hydrology from his point of view. Here below, please find his answer related to the use of models.

He says (my comments in italics):

“If I understood well your thesis, you support the idea that a good understanding and capacity of modelling biophysical phenomena are fundamental for making decisions, for instance about soil (my note: here used with the planners meaning), that are based on solid foundations. Specifically, it is needed to a correct quantification of the various phenomena, avoiding to use approaches too poorly approximate.
I agree with this thesis, which must be pursued with conviction by all, scientists and anyone. However, we do not have to go beyond a reasonable complexity, and fall in the Borges paradox to reproduce the Empire with a map the coincides identically with the Empire itself (see also here).
We can try to set these limits by considering two crucial elements: the use that will be done of the scientific knowledge (to disseminate, decide or, for instance, negotiate), and (not disjoint by the first), the perception of the same knowledge according to the users of the knowledge (see the scheme below). If perception is wrong nothing can be done.
Cash et al. (2013) and Clark et al (2011) suggest to consider the following three fundamental criteria referring to the perception of users of scientific knowledge: the perception of credibility (the scientific rigor perceived), relevance (of the specific problem), legitimacy (i.e. the capacity of inclusion of more points of view) of the sources.

We can take as an example of the Stanford's Natural Capital Project (NCP ( in the Water Fund in Latin America. These support governance mechanism and financial investments that guarantee clean water to downhill communities involving uphill communities. This works, more in general, by favouring collaboration among the stakeholder. NCP started to support scientifically the Water Funds, only after that first phase, by using a series of physical models of increasing complexity, called Tier1, Tier2, and Tier 3.

NCP approach is also transdisciplinary (Jahn et al., 2012, see also below^1) and includes at any stage of the process the stake holder. which is, actually considered the qualifying aspect of the process. In the experience of Water Funds, stakeholders were unable to understand the more complex biophysical models, and NCP had to implement simpler models called Tier0, ceasing the using of the complex models^2^3

This shows that in practice accepted scientific theories can find unespected difficulties, in relation to cognitive perceptions. "


  • Cash, D. W., W. C. Clark, F. Alcock, N. M. Dickson, N. Eckley, D. H. Guston, J. Jäger, and R. B. Mitchell. 2003. Knowledge systems for sustainable development. Proceedings of the National Academy of Sciences of the United States of America 100:8086–8091. 
  • Clark, W.C. et al., 2011. Inaugural Article: Knowledge Systems for Sustainable Development Special Feature Sackler Colloquium: Boundary work for sustainable development: Natural resource management at the Consultative Group on International Agricultural Research (CGIAR). Proceedings of the National Academy of Sciences.
  • Jahn, T., M. Bergmann, and F. Keil. 2012. Transdisciplinarity: Between mainstreaming and marginalization. Ecological Economics 79:1–10.


^1 Transdisciplinarity is a critical and self-reflexive research approach that relates societal with scientific problems; it produces new knowledge by integrating different scientific and extra scientific insights; its aim is to contribute to both societal and scientific progress; integration is the cognitive operation of establishing a novel, hitherto non-existent connection between the distinct epistemic, social–organizational, and communicative entities that make up the given problem context. (Jahn et al 2012)

^2 - This use of the simplest models is also diffuse in science, even if not always justified. Because some aspects of science are very specialistic, even specialists are not able to understand the reasons of complexity which goes beyond their strict domain of expertise, even they tend to favour the use of the simplest model, even when they are too simple (see Einstein citation).  Everyone of us should remember that if what s/he does not understand an explanation of a phenomenon in a snap, not necessarily the explanation is to throw away, but possibly require more application to be understood. Obviously sometimes model complexity was produced just because the Occam’s razor was not applied: this is the case when complexity is not welcomed. 

^3 - In my opinion, there is a basic cognitive limitation. To understand complexity (of even new paradigms) time and domestication is necessary. Aristotelians who looked inside Galileo’s telescope were not really able to see what Galileo saw. Their cognitive attitudes (their brains) were simply not prepared to, and they could not. Even scientists, supposed to be rational,  in face of unwanted results simply refuse to see them, and it is not uncommon the very famous colleagues died without accepting scientific statements against their own views, even if supported by overwhelming facts.

Wednesday, April 29, 2015

Earth Science Lectures at ICTP

ICTP stands for International Center for Theoretical Physics. The school is warranty of extremely high quality both in teaching and research. Looking at their product Eya for my using it in my classes, I saw their courses Tv. Among the many interesting things, to watch, there is a complete course on the Earth System that could be of interest also for hydrologist.  They derive from the


They say: "Disclaimer: ICTP publishes these lectures on the web and distribute them in digital form only for educational purposes. It will not endorse or sponsor any commercial product, service or activity, and does not permit the recorded material to be used for commercial purposes.
For more information about the courses, including the schedule of lessons, please visit the website of the ICTP Postgraduate Diploma Programme. "

Here they are the available topics for the Academic year 2014/2015

Mathematical Methods
(recorded hours: 12)
Mathematical Methods II
(recorded hours: 10)
Earth System Dynamics and Modelling I-II
(recorded hours: 48)
Wave Physics
(recorded hours: 24)
Earth System Thermodynamics
(recorded hours: 24)
Fluid Mechanics
(recorded hours: 24)
Physics of the Atmosphere
(recorded hours: 24)
Atmospheric Dynamics
(recorded hours: 24)
Physics of the Solid Earth
(recorded hours: 24)
Physics of the Oceans
(recorded hours: 20)
Space Geodesy and InSAR
(recorded hours: 24)
Theoretical Seismology
(recorded hours: 24)
Biogeochemical Cycles
(recorded hours: 28)
Observational and Computational Seismology
(recorded hours: 24)
Physics of Volcanoes
(recorded hours: 24)
Mechanics of Earthquakes and Tectonophysics
(recorded hours: 16)

(16 topics found, for a total of 374 hours)

Friday, April 17, 2015

The man who planted trees -part I

It was a few years ago that I came across the beautiful and inspiring movie  “The man who planted trees”  (in italian here)[1] . 
Read it or watch to it, it is a pleasure of a eco-novel which I find particularly adapt to Spring time. 
The novel raises several eco-hydrological issues, and in particular it poses a question to me: does planting trees change so greatly the hydrological cycle (and the ecosystem) ?  

Ecosystem Services (from the hydrological point of view)

From another point of view, a modern way to ask the same  question would be: which kind of ecosystem services can be obtained with a careful management of the environment, and  when the hydrological cycle is positively managed ? And, what kind of ecosystems services are activated or dumped as a consequence of soil cover change ?

Ecosystem services cover a broad range of agents, but in this case, I would restrict the focus to  understand the interactions between waters and vegetation (and, possibly opened to consider the carbon fluxes). 

It is believed that vegetation can serve for natural hazard and water cycle regulation. There is a generic consensus that forest ecosystems play a significant role in the prevention of soil erosion.  Specifically by cutting surface run-off and storing water they decrease the effects of extreme weather events and natural hazards like floods, storms, avalanches and landslides. Also they are believed to have an action of filtering waters producing cleaner waters and providing  groundwater recharge.  But how much of these beliefs can be quantitatively assessed ? 

The questions can be moved from forests to agricultural landscapes, a provisioning service themselves, without changing much of the hydrological aspects. The spatial unit, in this case is the cadastral unit, or something similar to it. As well as forests, agricultural fields can contribute to the carbon budget, to water quality, especially when they are riparian. 

Again the question is: how can we quantify it, in order to guide landscape management, precision agricolture, and doing forecasts on the effects of changes of soil use (and BTW the impacts of climate change) ?

So, why do not ask to  hydrologists [2] ;-) what they can say about the effects of vegetation on the hydrological cycle ? 

To any hydrologist it is clear that the key hydrological effects are related to evapotranspiration, of which I discussed in several posts. Dealing with it  there are several aspects to account for, among which I name three:

- Canopy transpiration (which can be differentiated in several layers: for instance, grass and plants are different for the way they uptake water). Usually it depends on the height of canopy, leaf area index (LAI), root depth, phenology  and plant's functional  specific parameters. Now there is quite an amount of literature on those parameters, but its real robustness and applicability is unknown.
Plants are different, but  plant types are really so different or it does exists an underlying optimization principle which ever optimize the use of water resources and therefore evapotranspiration for an ecosystem ? Some experimental evidence is going in this direction: but it is clearly a matter of equilibrium and time scales. Among plants there are differences, but it is not certainly possible to say that, for example, pine woods transpire more than larches: too many factors are playing a role. Dimension, characteristic and locations of the trees play possibly a major role than tree species and, this case may be it is the tree specific phenology the major source of difference among trees that share the same landscape.

- Soil evaporation (from bare soil and from below the canopy). It could appear pretty simple with respect to the thermodynamics of plants. Somehow pretty simple. However, whilst it affects only the surface layer, it is controlled by the water potential gradient of the soil column if atmospheric demand is sufficient. As recent papers by Dani Or and coworkers showed.   So very it is very coupled with bottom conditions. Evaporation from soils,  with their own biology,  is not always less than transpiration. In many conditions could be more, and separating it from canopy behaviour is not as simple. 
However, also the interactions,  with the overlaying atmosphere cannot be given for easily estimated. Either for soils and plants.

- Therefore, it is necessary to considering  a better description of the Boundary layer turbulence (which can be treated at different levels of approximations, also depending on the considered time and spatial scales).
 Per se, ET is a flux, a molecular diffusion driven flux, that we have at the surface of soil, of leaves, of water, or when it comes from sublimation, of snow or ice. The flux obeys to the laws of irreversibile thermodynamics processes, and is commanded by gradients of chemical potential. However, ET, as treated in hydrology, is  lumped together with transport, and theoretically derived from conceptualisations of the fluxes conceived a few decades ago. So, even if not simple, better quantitative estimates could derive by addressing fluxes and transport separately and numerically, which could actually benefit both the description of  stomatal and soil resistances, and of aerodynamics.

[1] - Giono, J. - The man who planted trees - L’uomo che piantava gli alberi, 1953
[2] - And I asked in particular to Giacomo Bertoldi

Wednesday, April 15, 2015

Best practices for Scientific Computing

I was actually looking for other stuff, but I across this paper on Plosone entitled:

Best practices for Scientific Computing, by Wilson et al., 2014

Enjoy it ! One of the Authors, Titus Brown has a blog that we follow (see the Related blog)