Wednesday, 28 January 2015

Modelling Rain to River over Africa - A Paper Review

By Chris Skinner @cloudskinner

I recently had my first research article published - "Hydrological modelling using satellite rainfall estimates in a sparsely gauged river basin: The need for whole-ensemble calibration". It has been accepted by the Journal of Hydrology, with which I am very pleased, and it is available to view for free until the 27th February 2015 here. If you are reading this after that date, I'm afraid you will need a subscription to the Journal to view it.

The problem the project was hoping to address is the issue of a lack of equipment available in many parts of the world which records rainfall. There are several methods of doing this, which I explain in an older post, but the most common ways are to use a network of rain-gauges or radar, both of which are expensive to install and maintain. For many nations, the measurement of rainfall is not a priority enough to invest in these networks but they would benefit greatly from having reasonable estimations of how much rain has fallen - it allows them to monitor water resources, forecast floods and droughts, and even predict how many crops will grow.

A Map of the Senegal River Basin. The rain-gauge network used for the study covered this wide area, yet the hydrological modelling focused on the Bakoye catchment (area in the south-east, containing both the Bakoye and Baoule rivers). (Image by Kmusser) 

"Senegalrivermap" by Kmusser - Own work, Elevation data from SRTM, drainage basin from GTOPO [1], all other features from Vector Map.. Licensed under CC BY-SA 3.0 via Wikimedia Commons -

My research focused on a section of the Senegal River Basin, a large area with only 81 rain-gauges across the wider region with which to estimate rainfall, a density of 1 gauge per 7,000km2. The density of the network is the equivalent of covering the UK with only 27 rain-gauges. There would be no way we could capture the complexity of our rainfall with so few gauges, and in reality the UK maintain a network of over 4,000 gauges with a density of 1 gauge per 76km2. In addition to this, the UK also maintain 15 rain recording radar stations, yet none are available to the Senegal Basin region.

Currently, the best way around this and to fill in the gap is to use information from satellites. For continuous observation of the same area it is not yet possible to directly observe rainfall, but it is possible to monitor other factors that indicate rainfall, particularly the temperature of clouds. Unlike the UK, this area of Africa generally only receives one type of rainfall, so there is a strong relationship between the temperature of the tops of clouds and whether they are raining - if the cloud is below a specified temperature it is assumed to be raining - the longer it remains below that threshold, the more intense the rain is thought to be. This is all calibrated against the very little rain gauge data that is available.

Example of a processed satellite image showing the number of hours each pixel of the image is below the specified rainfall (here it is -20c). The number of hours is known as the Cold Cloud Duration (CCD) and this is related to rainfall. The rain gauges used for the project are represented by the white circles.

Unfortunately, as this is not directly observing rainfall it can be wrong on occasion, and especially so when a user tries to make use of it at a smaller scale than the density of the rain gauge network. When the estimates are used as information for models, such as a hydrological model to estimate river flows, the errors in the rainfall estimates are passed on to that model. What we do know, however, is just how wrong the rainfall estimate could possibly be and this allows us to try and represent this.

The increasingly common way of representing this, what scientists call uncertainty, in the rainfall estimate is to take the value of how wrong it might be and to randomly produce several hundred different versions of the possible rainfall - each different but equally possible based on the information available to us. The users takes this ensemble rainfall estimate and feeds each member individually into the hydrological model and produces an ensemble of river flow estimates. Statistics can be used to suggest the probability of river flows for each step in the record.

View of the across the River Senegal in the Kayes region, downriver and north of the study site. (Image by Bourrichon)

This is where my research came into the process. Hydrological models need setting up before they are used and this is done via a process called calibration. You need a period of the record with rainfall data and recorded river flow data, and you vary adjustable values within the model (these are called parameters) until you get the closest match between the recorded river flows and what the model estimates. You then test this against another period of recorded river flow that was not used in the calibration to test its performance (known as validation or verification).

It is good practice to calibrate a model using the same data you intend to drive the model with. For example, the model will not perform as well if you calibrate it using rainfall data as estimated by rain gauges, but subsequently run the model using satellite rainfall estimates. This poses a particular problem for when you intend to run a hydrological model using ensemble rainfall estimates. This has previously been performed using either using the original satellite estimate (disregarding its uncertainty), or an average derived from the ensemble members. However, I tried the calibration using all the ensemble members individually, but assessing the model performance with them as a whole - this is called whole-ensemble calibration and named EnsAll in the paper.

Graph showing the mean error from the Pitman model, run separately with each ensemble member using data for the period 1997-2005. The model was calibrated using data for 1986-1996 using the whole-ensemble method (EnsAll), the daily mean rainfall estimate from all the ensemble members (EnsMean), and the theoretical mean of the ensembles (EnsExp). EnsAll clearly produces less error than the other two calibration methods on this measure.

The parameter values produced using the whole-ensemble calibration produced more accurate river flow estimates from the ensemble rainfall estimates than those produced by the other methods. In fact, the whole-ensemble calibration was the only method to produce 'reliable' estimates during validation, with the other methods proving no better than making an educated guess based on the rainfall record for the period.

I do hope that this provides you with a better understanding of the paper. If you want to know more of the technical details it is all in there, along with some nice statistics and some graphs to make Dave Gorman weep with joy. The research represents only a very small facet of the problem, which will require many more small facets to solve rather than one big one. I hope to produce a few more.

The paper can be viewed for free until 27/02/2015 using this link. The reference for the paper is - 

Skinner, C. J., Bellerby, T. J., Greatrex, H., and Grimes, D. I. F., 2015. Hydrological modelling using satellite rainfall estimates in a sparsely gauged river basin: The need for whole-ensemble calibration. Journal of Hydrology, 522, 110-122

Wednesday, 21 January 2015

Transition to sustainable building - does government policy help or hinder?

Following up on our previous blog posts (here) about green and sustainable building, this post describes a paper we’ve recently had published in Geoforum and which can be downloaded for *free* until the end of February 2015 (here).

Our paper explores recent changes which the UK government has made to how new buildings are encouraged to be ‘green’ or not.  Previously, the Code for Sustainable Homes was a voluntary set of guidelines which ‘measured’ how sustainable new homes were, based on whether they included solar panels, water recycling, bicycle storage and so on.  Now, the government has decided to abolish the Code for Sustainable Homes, and replace it with revised Building Regulations which means that instead of Code Level 6 (the highest and most sustainable) being the standard for new homes, it will now be Code Level 4, representing a significant change in how ‘green’ new homes should be.

The building sector is interesting due to its high contribution to greenhouse gas (GHG) emissions and associated concerns over enhanced global warming and climate change – as a result it has been the focus of governments who want to engender a shift towards greener ways of working and building.  Building homes and buildings differently could reduce our dependence on unsustainable products and materials.  Based on our research with green building companies, materials suppliers and architects, we argue that despite attempts by government to engender a full-scale shift in mainstream building methods, the relevant legislation is framed in ways that will not engender any substantial changes.

Photo courtesy of Pure Renewables.
Policies such as the Code for Sustainable Homes and the new revised (2013) building regulations encourage a particular approach to sustainable building which relies on technologies such as ground source heat pumps and solar panels rather than trying to change how people live in their homes (for example, how many televisions people have, whether they use a tumble drier and so on).  This sort of approach fails to address the kinds of lifestyle changes advocated by early green building pioneers, leading householders to rely on ‘smart house’ solutions without necessarily having to engage in behavioural change[i].  In addition the Code for Sustainable Homes only provides an assessment at one point in time and fails to address post-occupancy behaviour[ii], which may actually increase energy use as energy savings and lower bills encourage people to purchase new appliances which they can now ‘afford’ to run.

Despite general agreement on the shortcomings of policy, respondents had conflicting views on how green buildings should be defined, and on the best ways to implement such green buildings.  Respondents were critical of current UK legislation, and argue that its narrow conceptualisation fails to adequately encourage, or recognise, what they would consider to be green building forms that will contribute to substantial reductions in carbon emissions, nor does it respect locally appropriate building methods.

For our respondents, technologies such as solar panels were seen as very low on the list of priorities for green building and were seen as the ‘‘very icing on the cake once you’ve done everything else’’ (Interview, Material supplier).  By contrast, the aim of our respondents was to minimise energy demand at the outset and then look at how to further reduce that demand. The consequence was that they saw certain technologies as undesirable – ‘‘there’s certain things that we probably wouldn’t consider, which again are a bit greenwashy, like heat pumps particularly, air-source heat pumps particularly, they’re evil!’’ (Interview, Green builder).  For example, the respondent argued that air-source heat pumps could use more electricity than they saved at times of the year where there was a substantial difference between internal and external air temperatures (such as in the UK) meaning more energy was required to heat the air.

Solar panels on balconies, Vauban, Freiburg (Photo: Lara Güth)
In our paper we attempt to show that the process of changing current established practices towards more sustainable forms is a difficult process, even where there have been attempts by government to encourage such transformations through legislative action.  At one level, it can be argued that, as with other areas of green practice, such as organic food or renewable energy, there has been a shift towards greater environmental consciousness in the building sector. Thus, as one of our respondents noted:

‘‘I think that’s what the green movement, in a wider sense, has done; it’s kind of made things that were seen as a bit fringe and not quite acceptable, they’ve made them more acceptable.  They’ve made them more ‘every day’. . .you know, it’s not a strange thing anymore to talk about heating your house via the sun’’.  [Interview, Materials grower/supplier]

Brian Waite's straw bale house taking advantage
of warming winter sun (photo courtesy of Brian Waite)
However, the shift has so far been fairly minimal and taken on specific (technology-based) forms.  Far from inducing a ‘paradigm shift’ the regulatory framework in the UK for green building has effectively encouraged the adoption of an ‘eco-technic’ approach with an emphasis on technological, rather than holistic, solutions.  This tends to result in a rather business-as-usual approach rather than radically changing how we think about our homes and buildings.  We have also seen how, despite continued interest in encouraging green building, policy has not created the kind of regulatory certainty anticipated by the previous Labour government to drive change. Instead, UK zero carbon housing policy has been plagued by disagreement and inconsistency[iii].

Given the level of expertise that exists in niche organisations such as the AECB, as well as the demonstration effects of large scale building developments to zero carbon and Passivhaus standards in countries such as Germany, Austria, Sweden and Switzerland, there is scope for a major government-funded demonstration programme and/or to mandate higher standards for carbon reduction, such as the Passivhaus standard, in order to encourage greater levels of sustainability in the mainstream building companies. 

Low energy housing, Darmstadt, Germany (Photo: Kirstie O'Neill)
We conclude that, in policy terms, we should perhaps not be thinking of trying to create one single scenario for transitioning towards more sustainable homes, but to open up ‘possibility spaces’ for experimentation with new ideas and practices of green building. It is likely that there will be no ‘one best way’ to a green building sector, but a range of scenarios, which may cohere to incorporate different ways of achieving green building (as argued by our research respondents) and which would better respond to different geographical places.  Rather than rigid legislation, the role of policy should be to create the space for experimentation through collective means involving lots of different people as well as encouraging engagement with the people who actually live in the buildings.  This would recognise that processes of transitioning involve real world contestation, complexity and chaos rather than the more linear progression envisaged in UK Government policies for the building sector[iv].

[i] Reid, L.A., Houston, D., 2013. Low carbon housing: a ‘green’ wolf in sheep’s clothing? Housing Stud. 28(1), 1–9.
[ii] Greenwood, D., 2012. The challenge of policy coordination for sustainable sociotechnical transitions: the case of the zero-carbon homes agenda in
England. Environ. Plann. C 30, 162–179.
[iii], Accessed 13.03.14.
[iv] Raven, R.P.J.M., Verbong, G.P.J., Schilpzand, W.F., Witkamp, M.J., 2011. Translation mechanisms in socio-technical niches: a case study of Dutch river management. Technol. Anal. Strategic Manage. 23 (10), 1063–1078.

Wednesday, 14 January 2015

How do plants cope with changing temperature?

By Dr Lindsey Atkinson (@LJA_1)

Plants have evolved many specialised adaptations to enable them to live in a wide range of conditions but what happens when their environment changes?

Plants are sessile organisms, literally rooted to the spot, so if the conditions where they live become unfavourable they cannot move to a more favourable area.  For instance, they may be subject to changes in water or nutrients supply, light or temperature:  here I want to focus on temperature in particular. Plants experience climate with some seasonal variation but they may also be exposed to short-term fluctuations in temperature due to local weather conditions. These changes in temperature impact on the plant’s growth, function and development (phenology). In the long term adaptation may occur, or there may be a change in the range in which the species can live. However, in the short term, plants need to adjust to the local conditions to ensure survival, growth and ultimately reproduction.

It is important to understand how plants will respond to climate change as this will have impacts on biodiversity and also on crop productivity and quality, and hence food security.   In addition plants are major determinants of CO2 turnover in the atmosphere (Schimel et al. 2001) through the processes of photosynthesis and respiration.  Both of these processes are sensitive to temperature, with rates increasing with increased temperature. However, there may be an adjustment in the rate of the process to compensate for the initial change in temperature; this is known as acclimation and may moderate the response.

We can use our knowledge of how changing temperatures will affect photosynthesis and respiration at the leaf level of individual leaves to scale these processes up to predict the responses of ecosystems to global change.  For example, we incorporated thermal acclimation of respiration into a coupled-global climate vegetation model. The results indicated that while incorporating acclimation of respiration had little effect on predicted global atmospheric CO2 levels, the response varied between biomes which could have land use management implications (Atkin et al. 2008).

Arabidopsis thaliana  grown at 23oC in
controlled environment conditions
Even in a warmer world plants may experience a sudden drop in temperature: this could occur in the autumn at the onset of winter, or due to a late cold-spell in spring.  We wanted to know whether plants could continue to grow in these conditions so we grew Arabidopsis thaliana plants at 23oC and then shifted them to 5oC (Atkinson et al., 2014):  following the shift the growth rate was initially reduced to less than one third of that of warm grown plants.  However, growth subsequently recovered with the development of new leaves in the new conditions after about 14 days.  These new leaves had a cold phenotype which was important in the recovery in carbon metabolism in the cold.  The development of the new tissues was supported initially by use of stored nitrogen and relocation from pre-existing tissues but later by nitrogen obtained from the growth medium. This indicates that both the nitrogen status of the plant and the external nitrogen supply may be important in the acclimation of photosynthesis and respiration in the cold. 

The paper is available online at

Atkin OK, Atkinson LJ, Fisher RA, Campbell CD, Zaragoza-Castells J, Pitchford JW, Woodward FI, and Hurry VM (2008) Using temperature-dependent changes in leaf scaling relationships to quantitatively account for thermal acclimation of respiration in a coupled global climate-vegetation model.   Global Change Biology 14: 1-18 
Atkinson LJ, Sherlock DJ and Atkin OK (2014) Source of nitrogen associated with recovery of relative growth rate in Arabidopsis thaliana acclimated to sustained cold treatment. Plant, Cell and Environment Article first published online: 7 Dec 2014 | DOI: 10.1111/pce.12460
Schimel DS, House JI, Hibbard KA et al. (2001) Recent patterns and mechanisms of carbon exchange by terrestrial ecosystems.  Nature, 414, 169–172.

Wednesday, 7 January 2015

International Student Mobility: The Role of Social Networks

By Suzanne Beech (@suzanneebeech)

I have a new paper online early with Social and Cultural Geography, it is the second to come out of my PhD thesis on international higher education and the factors which influence students in their decision to study abroad. This paper focuses on one of the biggest factors effecting student mobility (and many other forms of mobility as well) - the role of social networks of friendship and kinship. It looks at the experience of 38 international students studying at three UK universities who were either interviewed or took part in a small focus group between March 2011 and February 2012. Each of the students that took part was enrolled on a diploma seeking programme of study (i.e. their period of time overseas was for the duration of their degree, rather than related to a temporary exchange or sojourn abroad). They came from 23 different countries and were studying both at undergraduate and postgraduate level. While I did not explicitly ask them about their socio-economic background it is likely that, given higher education mobility is often a very expensive pursuit, they came from relatively well-off backgrounds.  What was common to every one of the students that took part was the centrality of their friends and family in making their decision, their social networks were key to their mobility.

1.        What is a social network?

Social networks in this context are not limited to online social networks like Facebook and Twitter. The social networks in which my research is interested are much broader than this. At the most basic level they represent the multiple people (or actors) that a person communicates and interacts with in their day-to-day lives sharing resources and information in the process. Your social network is therefore anyone who you know well enough to engage in conversation, even if that conversation takes place along very limited lines. Any one person can, therefore, have hundreds of people in their social networks and can be part of numerous (sometimes overlapping) social networks e.g. your family could be one social network, your work colleagues another, the people in your tutorial group another and so on. International students, like everyone else, are part of complex networks of individuals all sharing information with one another. John Urry (2007; 2003) has written about how these networks shape mobility by creating connections between people through which they are able to share their experiences of being mobile. Members of a network are therefore able to tell others of the benefits of engaging in mobility and how to become more mobile themselves. It is therefore through networks that mobility often takes place.

2.       How do social networks influence mobility amongst international students?

My research shows that social networks operate in two ways in relation to international students. First, they can offer explicit advice and encouragement. This is perhaps less common than you may think, certainly most students did not admit to seeking out advice and encouragement – perhaps because international student mobility is often considered (at least socially) an individual activity where you go out and forge your own lifecourse – but there was evidence of some students actively turning to others for advice. Aimee from Canada for example spoke to people in her field about the value of an overseas degree, Subash and Sachin (from India) both turned to Facebook to find people who had also studied their course in the UK and Lily (from Malaysia) talked about the importance of being able to discuss her course with current students when on an open day.
More common, however, was the concept that social networks were about sharing the lived experiences of overseas mobility. In this context their social networks did not so much offer them advice and encouragement instead they began to normalise the process of going overseas. Asan (from Nepal) discussed how in his school it was normal for almost everyone to study abroad, suggesting a huge “95 per cent” went overseas (this is possibly an exaggeration, but whether literal or not it is clear that lots of people chose to do so). Marianna (from Greece) wanted to have the same experiences that a friend had when she studied in the UK. Hazel (from the USA) watched friends go backpacking in Europe and wanted to have a similar experience. As Urry (2007) suggests, they had built a greater awareness of travel which had normalised engaging in long term mobility, leading to point 3…

3.     Social networks establish cultures of mobility.

What is interesting is that these networks become self-perpetuating to an extent. More people study overseas and share their experience (either explicitly or implicitly) with their social networks. This then introduces more people to the idea of studying abroad, some of whom will explore the option and choose to study outside of their home country, who will then share their experience with their social networks and so on, and so on, and so on, and so on, and so on, and so on. It effectively establishes a culture of mobility amongst international students which normalises the process of studying overseas.

There was evidence of the importance of social networks amongst every student who took part in the interviews and focus groups for my research. This suggests that these relationships are critical to mobility. It did not seem to matter where the students came from, or their level of study, social networks were somehow active in all of their decisions’ to study overseas. They had created cultures of mobility for these students which had normalised the process of studying overseas.

My paper on International Student Mobility: The Role of Social Networks is currently online early with Social and Cultural Geography and is available for download here.


Urry, J. (2003). Social networks, travel and talk. British Journal of Sociology, 54, 155–175.

Urry, J. (2007). Mobilities. Polity Press: Cambridge.