Hydrological modelling and pizza making: why doesn’t mine look like the one in the picture?

Is this a question that you have asked yourself after following a recipe, for instance, to make pizza?

You have used the same ingredients and followed all the steps and still the result doesn’t look like the one in the picture…

Don’t worry: you are not alone! This is a common issue, and not only in cooking, but also in hydrological sciences, and in particular in hydrological modelling.

Most hydrological modelling studies are difficult to reproduce, even if one has access to the code and the data (Hutton et al., 2016). But why is this?

In this blog post, we will try to answer this question by using an analogy with pizza making.

Let’s imagine that we have a recipe together with all the ingredients to make pizza. Our aim is to make a pizza that looks like the one in the picture of the recipe.

This is a bit like someone wanting to reproduce the results reported in a scientific paper about a hydrological “rainfall-runoff” model. There, one would need to download the historical data (rainfall, temperature and river flows) and the model code used by the authors of the study.

However, in the same way as the recipe and the ingredients are just the start of the pizza making process, having the input data and the model code is only the start of the modelling process.

To get the pizza shown in the picture of the recipe, we first need to work the ingredients, i.e. knead the dough, proof and bake. And to get the simulated river flows shown in the study, we need to ‘work’ the data and the model code, i.e. do the model calibration, evaluation and final simulation.

Using the pizza making analogy, these are the correspondences between pizza making and hydrological modelling:

Pizza making                         Hydrological modelling

kitchen and cooking tools computer and software

ingredients                         historical data and computer code for model simulation

recipe                                 modelling process as described in a scientific paper or in a computer                                                         script / workflow

Step 1: Putting the ingredients together

Dough kneading

So, let’s start making the pizza. According to the recipe, we need to mix well the ingredients to get a dough and then we need to knead it. Kneading basically consists of pushing and stretching the dough many times and it can be done either manually or automatically (using a stand mixer).

The purpose of kneading is to develop the gluten proteins that create the structure and strength in the dough, and that allow for the trapping of gases and the rising of the dough.The recipe recommends using a stand mixer for the kneading, however if we don’t have one, we can do it manually.

The recipe says to knead until the dough is elastic and looks silky and soft. We then knead the dough until it looks like the one in the photo shown in the recipe.

Model calibration

Now, let’s start the modelling process. If the paper does not report the values of the model parameters, we can determine them through model calibration. Model calibration is a mathematical process that aims to tailor a general hydrological model to a particular basin. It involves running the model many times under different combinations of the parameter values, until one is found that matches well the flow records available for that basin. Similarly to kneading, model calibration can be manual, i.e. the modeller changes manually the values of the model parameters trying to find a combination that captures the patterns in the observed flows (Figure 1), or it can be automatic, i.e. a computer algorithm is used to search for the best combination of parameter values more quickly and comprehensively.

Figure 1 Manual model calibration. The river flows predicted by the model are represented by the blue line and the observed river flows by the black line (source: iRONS toolbox)

According to the study, the authors used an algorithm implemented in an open source software for the calibration. We can download and use the same software. However, if any error occurs and we cannot install it, we could decide to calibrate the model manually. According to the study, the Nash-Sutcliffe efficiency (NSE) function was used as numerical criteria to evaluate the calibration obtaining a value of 0.82 out of 1. We then do the manual calibration until we obtain NSE = 0.82.

(source: iRONS toolbox)

Step 2: Checking our work

Dough proofing

In pizza making, this step is called proofing or fermentation. In this stage, we place the dough somewhere warm, for example close to a heater, and let it rise. According to the recipe, the proofing will end after 3 hours or when the dough has doubled its volume.

The volume is important because it gives us an idea of how strong the dough is and how active the yeast is, and hence if the dough is ready for baking. We let our dough rise for 3 hours and we check. We find out that actually it has almost tripled in size… “even better!” we think.

Model evaluation

In hydrological modelling, this stage consists of running the model using the parameter values obtained by the calibration but now under a different set of temperature and rainfall records. If the differences between estimated and observed flows are still low, then our calibrated model is able to predict river flows under meteorological conditions different from the one to which it was calibrated. This makes us more confident that it will work well also under future meteorological conditions. According to the study, the evaluation gave a NSE = 0.78. We then run our calibrated model fed by the evaluation data and we get a NSE = 0.80… “even better!” we think.

Step 3: Delivering the product!

Pizza baking

Finally, we are ready to shape the dough, add the toppings and bake our pizza. According to the recipe, we should shape the dough into a round and thin pie. This takes some time as our dough keeps breaking when stretched, but we finally manage to make it into a kind of rounded shape. We then add the toppings and bake our pizza.

Ten minutes later we take the pizza out of the oven and… it looks completely different from the one in the picture of the recipe! … but at least it looks like a pizza…

(Source: flickr.com)

River flow simulation

And finally, after calibrating and evaluating our model, we are ready to use it to simulate recreate the same river flow predictions as shown in the results of the paper. In that study, they forced the model with seasonal forecasts of rainfall and temperature that are available from the website of the European Centre for Medium-range Weather Forecasts (ECMWF).

Downloading the forecasts takes some time because we need to write two scripts, one to download the data and one to pre-process them to be suitable for our basin (so called “bias correction”). After a few hours we are ready to run the simulation and… it looks completely different from the hydrograph shown in the study! … but at least it looks like a hydrograph…

Why we never get the exact same result?

Here are some possible explanations for our inability to exactly reproduce pizzas or modelling results:

  • We may have not kneaded the dough enough or kneaded it too much; or we may have thought that the dough was ready when it wasn’t. Similarly, in modelling, we may have stopped the calibration process too early or too late (so called “over-fitting” of the data).
  • The recipe does not provide sufficient information on how to test the dough; for example, it does not say how wet or elastic the dough should be after kneading. Similarly, in modelling, a paper may not provide sufficient information about model testing as, for instance, the model performance for different variables and different metrics.
  • We don’t have the same cooking tools as those used by the recipe’s authors; for example, we don’t have the same brand of the stand mixer or the oven. Similarly, in modelling we may use a different hardware or operating system, which means calculations may differ due to different machine precision or slightly different versions of the same software tools/dependencies.
  • Small changes in the pizza making process, such as ingredients quantities, temperature and humidity, can lead to significant changes in the final result, particularly because some processes, such as kneading, are very sensitive to small changes in conditions. Similarly, small changes in the modelling process, such as in the model setup or pre-processing of the data, can lead to rather different results.

In conclusion…

Setting up a hydrological model involves the use of different software packages, which often exist in different versions, and requires many adjustments and choices to tailor the model to a specific place. So how do we achieve reproducibility in practice? Sharing code and data is essential, but often is not enough. Sufficient information should also be provided to understand what the model code does, and whether it does it correctly when used by others. This may sound like a big task, but the good news is that we have increasingly powerful tools to efficiently develop rich and interactive documentation. And some of these tools, such as R Markdown or Jupyter Notebooks, and the online platforms that support them such as Binder, enable us not only to share data and code but also the full computational environment in which results are produced – so that others have access not only to our recipes but can directly cook in our kitchen.


This blog has been reposted with kind permission from the authors, Cabot Institute for the Environment members Dr Andres Peñuela, Dr Valentina Noacco and Dr Francesca Pianosi. View the original post on the EGU blog site.

Andres Peñuela is a Research Associate in the Water and Environmental Engineering research group at the University of Bristol. His main research interest is the development and application of models and tools to improve our understanding on the hydrological and human-impacted processes affecting water resources and water systems and to support sustainable management and knowledge transfer




Valentina Noacco is a Senior Research Associate in the Water and Environmental Engineering research group at the University of Bristol. Her main research interest is the development of tools and workflows to transfer sensitivity analysis methods and knowledge to industrial practitioners. This knowledge transfer aims at improving the consideration of uncertainty in mathematical models used in industry




Francesca Pianosi is a Senior Lecturer in Water and Environmental Engineering at the University of Bristol. Her expertise is in the application of mathematical modelling to hydrology and water systems. Her current research mainly focuses on two areas: modelling and multi-objective optimisation of water resource systems, and uncertainty and sensitivity analysis of mathematical models.




Cooking with electricity in Nepal

PhD student Will Clements tells us how switching from cooking with biomass to cooking with electricity is saving time and saving lives in Nepal.

Sustainable Development Goal 7 calls for affordable reliable access to modern energy. However, around 3 billion people still use biomass for cooking. Smoky kitchens – indoor air pollution due to biomass cooking emissions – account for the premature deaths of around 4 million people every year. The burden of firewood collection almost always falls on women and girls, who must often travel long distances exposed to the risk of physical and sexual violence. The gravity of the problem is clear.

Wood stove in a household in Simli, a remote rural community in western Nepal. Credit: KAPEG/PEEDA

Electric cooking is a safe, clean alternative which reduces greenhouse gas emissions and frees up time so that women and girls can work, study and spend more time doing what they want.

In Nepal, many off-grid rural communities are powered by micro-hydropower (MHP) mini-grids, which are capable of providing electricity to hundreds or thousands of households, but often operate close to full capacity at peak times and are subject to brownouts and blackouts.

A project to investigate electric cooking in Nepali mini-grids was implemented in the summer of 2018 by a collaboration between Kathmandu Alternative Power and Energy Group (KAPEG), People Energy and Environment Development Association (PEEDA) and the University of Bristol in a rural village called Simli in Western Nepal. Data on what, when and how ten families cooked was recorded for a month, at first with their wood-burning stoves, and then with electric hobs after they had received training on how to use them.

A typical MHP plant in the remote village of Ektappa, Ilam in Nepal. Credit: Sam Williamson

When cooked with firewood, a typical meal of dal and rice required an average of 12 kWh of energy for five people, which is around the energy consumption of a typical kettle if used continuously for six hours! On the other hand, when cooked on the induction hobs this figure was just 0.5 kWh, around a third of the energy consumed when you have a hot shower for 10 minutes.

However, even at this high efficiency, there was insufficient spare power in the mini-grid for all the participants to cook at the same time, so they experienced power cuts which led to undercooked food and hungry families.

Many participants reverted to their wood stoves when the electricity supply failed them, and this with only ten of 450 households in the village trying to cook with electricity. The project highlighted the key challenge – how can hundreds of families cook with electricity on mini-grids with limited power?

In April 2019, the £39.8 million DFID funded Modern Energy Cooking Services (MECS) programme launched. The MECS Challenge Fund supported the Nepal and Bristol collaboration to investigate off-grid MHP cooking in Nepal further.

A study participant using a pressure cooker on an induction hob. Credit: KAPEG/PEEDA

A study participant using a pressure cooker on an induction hob. Credit: KAPEG/PEEDA
The project expands on the previous project by refining data collection methods to obtain high quality data on both Nepali cooking practices and MHP behaviour, understanding and assessing the potential and effect of electric cooking on Nepali MHP mini-grids, and using the collected data to investigate how batteries could be used to enable the cooking load to be averaged throughout the day so that many more families can cook with electricity on limited power grids.

MHP differs greatly from solar PV and wind power in that it produces constant power throughout the day and night, providing an unexplored prospect for electric cooking. Furthermore, this 24/7 nature of MHP means that there is a lot of unused energy generated during the night and off-peak periods which could be used for cooking, if it could be stored. Therefore, battery-powered cooking is at the forefront of this project.

Testing induction hobs in the MHP powerhouse. Credit: KAPEG/PEEDA

Collected data will be used to facilitate a design methodology for a battery electric cooking system for future projects, evaluating size, location and distribution of storage, as well as required changes to the mini-grid infrastructure.

Furthermore, a battery cooking laboratory is being set up in the PEEDA office in Kathmandu to investigate the technical challenges of cooking Nepali meals from batteries.

The baseline phase – where participants’ usual cooking is recorded for two weeks – is already complete and preparations for the transition phase are underway where electric stoves are given to participants and they are trained on how to cook with them.

We will be heading to Kathmandu to help with the preparations, and the team will shortly begin the next phase in Tari, Solukhumbu, Eastern Nepal.

The project will continue the journey towards enabling widespread adoption of electric cooking in Nepali MHP mini-grids, the wider Nepali national grid and grids of all sizes across the world.

This blog is written by Will Clements and has been republished from the Faculty of Engineering blog. View the original blog. Will studied Engineering Design at Bristol University and, after volunteering with Balloon Ventures as part of the International Citizen Service, returned for a PhD with the Electrical Energy Management Research Group supervised by Caboteer Dr Sam Williamson. Will is working to enable widespread adoption of electric cooking in developing communities, focusing on mini-grids in Nepal.

The opinions expressed in this blog are those of the author and do not necessarily reflect the official policy or position of UKAid.

Will Clements


Uncomfortable home truths: Why Britain urgently needs a low carbon heat strategy

A new report backed by MPs and launched by Minister for Climate Change Lord Duncan on 15 October 2019, calls for an urgent Green Heat Roadmap by 2020 to scale low carbon heating technologies and help Britain’s homeowners access the advice they need to take smarter greener choices on heating their homes.  The year-long study by UK think-tank Policy Connect warns that the UK will miss its 2050 net-zero climate target “unless radical changes in housing policy, energy policy and climate policy are prioritised”. Dr Colin Nolden was at the launch on behalf of the Cabot Institute for the Environment and blogs here on the most interesting highlights of the report and questions raised.


Policy Connect had invited a range of industry, policy, academic and civil society representatives to the launch of their Uncomfortable Home Truths report. The keynote, no less than Lord Duncan of Springbank, Minister for Climate Change, and the high-level panel consisting of Maxine Frerk, Grid Edge Policy (Chair), Alan Brown MP, House of Commons (SNP), Dr Alan Whitehead MP, House of Commons (Labour), Dhara Vyas, Citizens Advice, Adam Turk, BAXI Heating (sponsor) and Mike Foster, EUA (Energy & Utilities Alliance), (sponsor), had been briefed to answer tough questions from the crowd given the UK’s poor track record in the area of heat and home decarbonisation.

The event started with an introduction by Jonathan Shaw, Chief Executive of Policy Connect, who introduced the panel and officially launched the report. Uncomfortable Home Truths is the third report of the Future Gas Series, the first two of which focused on low-carbon gas options. This last report of the series shifts the focus from particular technologies and vectors towards heating, households and consumers. Jonathan subsequently introduced the keynote speaker Lord Duncan of Springbank, Minister for Climate Change.

Lord Duncan supported the publication of this report as timely and relevant especially in relation to the heat policy roadmap that government intends to publish in 2020. He stressed the importance of a cultural shift which needs to take place to start addressing the issue of heat at household and consumer level. He was adamant that the government was aligning its policies and strategies with its zero-carbon target according to the Committee on Climate Change and guided by science and policy. In this context he bemoaned the drive by some country representatives to put into question the targets of the Paris Agreement on Climate Change which he had witnessed as the UK’s key representative at the run-up to COP25 in Chile. The 2020 roadmap will report on the decisions which will need to be taken in homes and in technology networks, ranging from heat pumps to hydrogen and low-carbon electricity to support their decarbonisation. It requires cross-party support while depending on more research and learning from successful examples in other European countries.

Although Lord Duncan suggested that ‘it’s easier to decarbonise a power plant than a terraced house’, he told the audience to take encouragement from the fuel shift from coal towards gas starting half a century ago. But in this context he once again stressed the cultural shift which needs to go hand-in-hand with government commitment and technological progression, using the example of TV-chefs shunning electric hobs as an indication of our cultural affinity for gas. As long as heating and cooking are framed around fossil fuels, there is little space in the cultural imagination to encourage a shift towards more sustainable energy sources.

“The example of TV-chefs shunning electric hobs is an indication of our cultural affinity for gas”. Image source.

Among the questions following the keynote, one quizzed Lord Duncan about the process and politics of outsourcing carbon emissions. Lord Duncan stressed his support of Border Carbon Adjustments compliant with EU and global carbon policy ‘in lock-step with our partners’ to ensure that carbon emissions are not simply exported, which appears to support the carbon club concept. Another question targeted the UK’s favourable regulatory environment that has been created around gas, which has resulted in the EU’s lowest gas prices, while electricity prices are highest in Europe, due, among other things, to Climate Change Levies, which do not apply to gas, increasing by 46% on 1 April 2019. Lord Duncan pointed towards the ongoing review of policies ahead of the publication of the 2020 heat roadmap which will hopefully take a more vector- and technology-neutral approach. A subsequent rebuttal by a Committee on Climate Change (CCC) representative stressed the CCCs recommendation to balance policy cost between gas and electricity as on average only 20,000 heat pumps are sold in the UK every year (compared to 7 times as many in Sweden) yet the Renewable Heat Incentive is about to be terminated without an adequate replacement to support the diffusion of low-carbon electric heating technologies.

Lord Duncan stressed the need to create a simple ‘road’ which does not fall with changes in policy and once again emphasized the need for a cross-party road to support the creation of a low-carbon heating pathway. A UKERC representative asked about the government approach to real-world data as opposed to modelling exercises and their support for collaborative research projects as both modelling and competitive approaches have failed, especially in relation to Carbon Capture and Storage. Lord Duncan responded that the UK is already collaborating with Denmark and Norway on CCS and that more money is being invested into scalable and replicable demonstrators.

Following an admission wrapped in metaphors that a change in government might be around the corner and that roadmaps need to outlast such changes, Lord Duncan departed to make way for Joanna Furtado, lead author of the Policy Connect report. She gave a very concise overview of the main findings and recommendations in the report:

  • The 80% 2050 carbon emission reduction target relative to 1990 already required over 20,000 households to switch to low-carbon heating every week between 2025 and 2050. The zero-carbon target requires even more rapid decarbonisation yet the most successful policy constellations to date have only succeeded in encouraging 2,000 households to switch to low-carbon heating every week.
  • This emphasizes the importance of households and citizens but many barriers to their engagement persist such as privacy issues, disruption associated with implementation, uncertainly, low priority, lack of awareness and confusion around best approaches, opportunities, regulations and support.
  • Despite the focus on households, large-scale rollout also requires the development of supply chains so at-scale demonstrations need to go hand-in-hand with protection and engagement of households by increasing the visibility of successful approaches. Community-led and local approaches have an important role to play but better monitoring is required to differentiate between more and less successful approaches.
  • Protection needs to be changed to facilitate the inclusion of innovative technologies which are rarely covered while installers need to be trained to build confidence in their installations.
  • Regional intermediaries, such as those in Scotland and Wales, need to be established to coordinate these efforts locally while at national level a central delivery body such as the one established for the 2020 Olympics in London needs to coordinate the actions of the regional intermediaries.
  • Ultimately, social aspects are critical to the delivery of low-carbon heat, ranging from the central delivery body through regional intermediaries down to households and citizens.


Image source.

Chaired by Maxine Frerk of Grid Edge Policy, the panel discussion kicked off with Alan Brown who stressed the urgency of the heating decarbonisation issue as encapsulated by Greta Thunberg and Extinction Rebellion and the need to operationalize the climate emergency into actions. He called for innovation in the gas grid in line with cautions Health and Safety Regulation alterations. Costs also need to be socialised to ensure that the low-carbon transition does not increase fuel poverty. His final point stressed the need reorganize government to make climate change and decarbonisation a number 1 priority.

Dr Alan Whitehead, who has been involved with the APPCCG from the beginning, emphasized how discussions around heat decarbonisation have progressed significantly in recent years and especially since the publication of the first report of this series. He suggested that the newest report writes the government roadmap for them. In relation to the wider context of decarbonising heat, Alan Whitehead encouraged a mainstreaming of heating literacy similar to the growing awareness of plastic. He also stressed how far the UK is lagging behind compared to other countries and this will be reflected in upcoming policies and roadmaps. As his final point Alan Whitehead cautioned that the low-intrusion option of gas-boiler upgrades from biomethane to hydrogen ignores the fact that greater change is necessary for the achievement of the zero-carbon target although he conceded that customer acceptance of gas engineer intervention appears to be high.

Dhara Vyas presented Citizens Advice perspective by stressing the importance of the citizen-consumer focus. Their research has revealed a lack of understanding among landlords and tenants of the rules and regulations that govern heat. She suggested that engagement with the public from the outset is essential to protect consumers as people are not sufficiently engaged with heating and energy in general. Even for experts it is very difficult to navigate all aspects of energy due to the high transaction costs associated with engagement to enable a transition on the scale required by government targets.

Finally, representatives of the two sponsors BAXI and the Energy & Utility Alliance made a rallying call for the transition of the gas grid towards hydrogen. Adam Turk emphasized the need to legislate and innovate appropriately to ensure that the 84% of households that are connected to the gas grid can receive upgrades to their boilers to make them hydrogen ready. Similarly, Mike Foster suggested that such an upgrade now takes less than 1 hour and that the gas industry already engages around 2 million consumers a year. Both suggested that the gas industry is well placed to put consumers at the heart of action. They were supported by several members of the audience who pointed towards the 150,000 trained gas service engineers and the ongoing distribution infrastructure upgrades towards plastic piping which facilitate a transition towards hydrogen. Other members of the audience, on the other hand, placed more emphasis on energy efficiency and the question of trust.

Sponsorship of the Institution of Gas Engineers & Managers, EUC (Energy & Utility Alliance) and BAXI Heating was evident in the title Future Gas Series and support for hydrogen and ‘minimal homeowner disruption’ boiler conversion to support this vector shift among members of the audience was evident. Nevertheless, several panel members, members of the audience and, above all, Lord Duncan of Springbank, stressed the need to consider a wider range of options to achieve the zero-carbon target. Electrification and heat pumps in particular were the most prominent among these options. Energy efficiency and reductions in energy demand, as is usual at such events, barely received a mention. I guess it’s difficult to cut a ribbon when there’s less of something as opposed to something new and shiny?

This blog is written by Dr Colin Nolden, Vice-Chancellor’s Fellow, University of Bristol Law School and Cabot Institute for the Environment.

Colin Nolden

Indoor air pollution: The ‘killer in the kitchen’

Image credit Clean Cooking Alliance.

Approximately 3 billion people around the world rely on biomass fuels such as wood, charcoal and animal dung which they burn on open fires and using inefficient stoves to meet their daily cooking needs.

Relying on these types of fuels and cooking technologies is a major contributor to indoor air pollution and has serious negative health impacts, including acute respiratory illnesses, pneumonia, strokes, cataracts, heart disease and cancer.

The World Health Organization estimates that indoor air pollution causes nearly 4 million premature deaths annually worldwide – more than the deaths caused by malaria and tuberculosis combined. This led the World Health Organization to label household air pollution “The Killer in the Kitchen”.

As illustrated on the map below, most deaths from indoor air pollution occur in low- and middle-income countries across Africa and Asia. Women and children are disproportionately exposed to the risks of indoor air pollution as they typically spend the most time cooking.

Number of deaths attributable to indoor air pollution in 2017. Image credit Our World in Data.
Replacing open fires and inefficient stoves with modern, cleaner solutions is essential to reduce indoor air pollution and personal exposure to emissions. However, research suggests that only significant reductions in exposure can tangibly reduce negative health impacts.
The Clean Cooking Alliance, established in 2010, has focused mainly on the dissemination of improved cookstoves (ICS) – wood-burning or charcoal stoves designed to be much more efficient than more traditional models – with some success.
Randomised control trials of sole use of ICS have shown reductions in pneumonia and the duration of respiratory infections in children. However, other studies, including some funded by the Alliance, have shown that ICS have not performed well enough in the field to sufficiently reduce indoor air pollution to lessen health risks such as pneumonia and heart disease.
Alternative fuels such as liquid petroleum gas (LPG), biogas and ethanol present other options for cooking with LPG already prevalent in many countries across the world.
LPG is clean-burning and produces much less carbon dioxide than burning biomass but is still a fossil fuel.
Biogas is a clean, renewable fuel made from organic waste, and ethanol is a clean biofuel made from a variety of feedstocks.
Image credit PEEDA

Electric cooking, once seen as a pipe dream for developing countries, is becoming more feasible and affordable due to improvements and reductions in costs of technologies like solar panels and batteries.

Improved cookstoves, alternative fuels and electric cooking have been gaining traction but there is still a long way to go to solving the deadly problem of indoor air pollution.
This blog is written by Cabot Institute member Peter Thomas, Faculty of Engineering, University of Bristol. Peter’s research focusses on access to energy in humanitarian relief. This blog is co-written by Will Clements, Faculty of Engineering.