Tuesday, September 28, 2021

Modelling the River Po (Poster @SII Hydrology days 2021)

 Wow, this will be the first meeting I will attend in more than two years. The are the Italian Hydrological Society (SII) days 2021 and will be held in Naples. We will be presenting a couple of interesting thing. This is the first poster on the modelling of the largest river basin in Italy, which is the topic of the poster here below. The poster should be self-explaining. 

Clicking on the above figure, you can download the high resolution pdf. 

Monday, September 20, 2021

Notes for an incoming hydrology book, Contemporary Hydrology - a Preface

 What’s on Earth is hydrology ? It is the science that studies the movements of water, from the atmosphere to the ground and into the ground and then back to the atmosphere again. This book does not aim to cover all the variety of issues and topics the movement of water causes but is mainly concerned with keeping the material simple and possibly concise. Insights are left to notes and to appropriate literature.

Everyone sees water moving on the Earth surface, maybe excluding those who lives in deserts, and it looks like the it should be easy to get a quantitative mathematical description of water movements: but this is not the case! Even the channelized flow, the simplest of the water flows, shows a great complexity, due to the turbulent nature of the flow and the variety of boundaries in which the water is “constrained”. I have put constrained among quotes “” because water is never really constrained. It goes everywhere, sometimes very slowly, compared to the subjective time of our human actions. Other  flows needs to cope with the medium where water flows, for instance the porous soils, the underground, the plants vessels.
More than that, water on Earth is usually liquid, solid, in form of ice or snow, vapor and each of the phase of water  interacts with and transform into the others. The complexity of phases is just one side of the multifaceted dynamics of water because the elementary physics or thermodynamics of water movements at the centimeter or smaller spatial scale (but how the small is small if, for instances, pores in soil can be micrometers and intercellular space in leaves nanometers ? ) dynamically organizes when we look at the movements at the meter scale and reorganizes at the decameters scale and reorganizes again at the hectare, and, again and again, at kilometers, up to the dimensions of continents. In this reorganization some feature of the elementary motion is loosed while some other feature emerges as fundamental. We could say that the core of contemporary hydrology is in getting a reason of these scales behavior in heterogeneous, i.e. affected by  a great variety of small causes, environment. Galilean science is the light to move among the variety. However hydrologists, the scientists who study and evolve Hydrology’s understanding, rarely can setup experiments (they do, obviously, in the labs) which are really answering the questions, because simplifications and distortion, implicit in other physical sciences branches do not work when you have to deal with a transpiring plant or when the inanimate (?) but complex channel networks forms. Hydrology is mostly observed and recorded, in a sequence of single cases, each one at best slightly different from the others and often very different from the others. Therefore from where we start ? A few certainties we have: mass conservation is the first. We give it for granted but it was recognized more than two centuries ago and its status was even more uncertain in hydrology up to Dalton’s research. The second is the energy conservation, which is in fact more elusive, since the difficulty to estimate some of its parts is bigger than the one to measure mass flow. Those two statements seem so obvious when  enunciated but when we come to measure the mass budget and the energy budget closure troubles begin. Historically, actually, their were not the center of scientists’ research, because this was concentrated merely on fluxes determination, like the river discharge, the evaporative transport, or groundwater flow, at most. However, let’s say, that this book is very much concerned with the closure of these budgets, than concentrating on any of the fluxes, on which actually various sub-disciplines flourished in the past.
Newtonian physics rules, when messing with hydrology, but also the explication of the second law of the dynamics is largely simplified, even in the recent treatments, because of the pitfalls it hides when dealing with simple mechanical systems but that reveals in their whole complexity when the case of water fluxes is the topic.
The nature of the measured hydrological quantities is usually presenting a  degree of randomness, even if their physics is known to be deterministic. This apparent randomness is certainly due to the high number of degree of freedom that the fluid nature of the water, either liquid or gaseous, brings, but also of the uncountable histories that water encounters in its travel. Probably it is not true randomness, is maybe random-mess, because of the structure of the medium water crosses.
If then it is true that determinism is at the core of the hydrological thermodynamics (or maybe saying “thermodynamics” we are contradicting ourselves?) the analysis of the matter lives at the faint light of statistics for almost every phenomenon.  Therefore, almost always hydrologists have hard times to deduce  patterns from very uncertain information. All of these issues in fact are those that makes this science one of the most fascinating of the contemporary science.

Sunday, September 19, 2021

What I did in research the last five years, 2016-2021

 In the last ten years I focused on building a reliable system for doing hydrology by computer. This systems learns from the implementation of the process-based GEOtop and is based on the framework developed by ARS/USDA called OMS3. The new system is called GEOframe

I have been concerned with the fact that many results claimed on the basis of computer simulations were, in fact, not properly reliable and verifiable, do to lack of software engineering, description of the internals of the tools and availability to researchers. Moreover, also the goodness experimental science is quite dependent on the capability and reliability of models.  In my experience with the model GEOtop so far, when there have been discrepancies between data and the model, most of the time the model was right and the experiment imprecise. Sometimes though was the model GEOtop (or other that we used) wrong and we worked to improve it. Models have to be robust, reliable, realistic and their results reproducible (R4). The new system GEOframe, which is built on these premises, is not a model though. It can fit several modelling solutions and it is actually is agnostic with respect to the methods. It is designed to offer a platform to compare different modelling strategies, lumped modelling, process-grid-based modelling and whatever but avoiding to redo any time the unnecessary.
We used some ML technique in the process of calibration and we implemented also a ANN framework (in OMS3) but that part is underdeveloped at that moment. (If we expand to much, we bleed).  

The older part of the GEOframe system contains lumped based types of models. However, we have recently implemented a solver of Richards 1D [0] and 2D (paper in writing) and 3D (software in deployment). The latter implement a new algorithm for integration of non linear PDE systems which always converges and can naturally switch between groundwater, vadose zone and surface water. Soil can be hot, warm and frozen  without problems (the latter is in deployment). Besides this I worked underground in having a better estimation of evaporation and transpiration. I published very little with respect the amount of work I did on these subjects, but disentangling the theory, the misconceptions, the scale issue was (is) not very easy, and took its time. I have a first (not completely satisfactory paper, from my point of view,  on this topic, just published on Water [1] , but better ones are going to be written in the Fall 2021 and in the 2022. Finally I worked on disentagling the theory of travel time residence time. We have some paper on it, since 2016 [2,3,4,5] which are also connected to a new way to categorize and, before of it, representing  lumped-semi-distributed  models [6] in order to be able to produce some quantitative reasoning about models structure. I did not pursued very much applied work but with GEOframe growing we were able to produce some nice applications on the Posina catchment [6] (~110 km2), Blue Nile (~175000 km2) [7]. These applications, could be the basis for a comparison of traditional and ML methods. We have also ongoing  the modelling of the largest river basin in Italy, the Po river (~75000km2) and the Nera catchment (closed at some hundreds of square kilometers),  being  very interesting because affected by karst.  Those  latter two catchments could be possible candidates for applying ML techniques and doing performance comparisons, once we have collected the appropriate data. Notably in the last work (actually since the implementation of GEOtop) working on the catchment meant for me working on the water budget of which the discharge is just one element completed by evaporation, transpiration and heat turbulent transfer. I viewed the use of the energy budget necessary to describe irrigation needs by crops and vegetation in this changing climate era, and in general as a tool to support a more complete view of the hydrological cycle.