Tuesday, 24 February 2015

CEH lakes research presented at 2015 Aquatic Sciences Meeting

A number of CEH's lake researchers are in attendance at the 2015 Aquatic Sciences Meeting taking place this week in Granada, Spain (22-27 February). See below for details of oral and poster presentations. You can follow updates from the meeting on Twitter with #ASLO2015.

Photo: CEH scientists carrying out restoration research at a lake in Scotland


Related links

2015 ASLO Aquatic Sciences Meeting

UK Lake Restoration research at CEH

Lake Ecosystems research at CEH

Wednesday, 18 February 2015

New dataset released: Integrated Hydrological Units of the United Kingdom

Our colleagues in the National River Flow Archive (NRFA) have released a new, freely available dataset of spatial reference units for hydrological purposes, called "Integrated Hydrological Units of the United Kingdom". Filip Kral explains more:

"This dataset will aid hydrological analysis and water management in the UK by providing a consistent, nationwide framework for segregating river catchments into component parts. It also serves as a reference list of major river names and, by indicating which units are connected, it can be used to trace the flow of rivers across the country.

The Integrated Hydrological Units (IHU) of the United Kingdom (UK) define spatial geographical reference units for hydrological purposes

Researchers and organisations working to improve catchment management have already expressed interest in the dataset which we believe will become popular in the water industry and wider hydrological science community, thanks also to its open data license.

Integrated Hydrological Units (IHU) of the United Kingdom (UK) consists of four polygon layers: Hydrometric Areas, Groups, Sections, and Catchments. Each layer represents a different level of spatial detail.

  • The coarsest level, Hydrometric Areas, consists of more than 100 polygons corresponding to the spatial units used to organise river flow measurement and hydrometric data collection in the UK (for example, HA023 represents the Tyne in Northumberland). 
  • Each Hydrometric Area consists of one or more Groups (405 in total), which carry names derived from the major rivers flowing through, in, and out of each group, for example HA023G03 is Tyne (North Tyne to tidal limits) Northumberland. 
  • Each Group consists of even smaller units – Sections (more than 500,000 in total). A Section is the drainage area of a watercourse between two confluences, for example HA023G03S0024 is Tyne (Devil’s Water to March Burn). 
  • Each Section is associated with one Catchment representing the compound catchment upstream of the Section outflow point.
Tyne Bridge, Newcastle

Historically, Hydrometric Areas were the primary reference units used by the NRFA to manage hydrometric data in the UK. IHU is a new release of the Hydrometric Area definition supplemented with finer scale units, all derived using the CEH Integrated Hydrological Terrain Model. Plans are being developed to utilise the IHU to help users explore other datasets produced by the NRFA and CEH’s Environmental Information Data Centre."

The dataset is available on the EIDC Hub.

Filip Kral

Related links

National River Flow Archive


Wednesday, 4 February 2015

Plant hormone signals and climate models, plus a mathematical surprise

A new study examining the links between soil moisture and leaf stomata should be of interest to both plant physiologists and climate modellers. It was published in the journal Ecological Modelling (27 January 2015, Ecological Modelling 300 (2015) 81–88), and is open access, so freely accessible. Below the lead author, Dr Chris Huntingford of the Centre for Ecology & Hydrology (CEH), explains what they did and how the analysis reveals an unexpected mathematical twist:

“A small team of us have just published a paper on assessing how the equations link together that describe ABA (abscisic acid) messaging in plant systems. Possibly more than most pieces of mathematical analysis, our study turned into a bit of an adventure, including an unexpected outcome.

ABA is a hormone which passes through vegetation, and provides a signal to leaf stomata regarding the amount of soil moisture available. Stomata control both evaporation and photosynthesis and, if soil moisture is depleted, then generally plants close such pores as a protection mechanism during periods of drought.

Climate models are designed to estimate adjustments in near-surface temperature and humidity (amongst many other quantities) in response to raised atmospheric greenhouse gas concentrations. However the land surface is a fully coupled part of the climate system, not simply responding to any imposed adjustment to weather conditions, but also affecting them. This can be through multiple feedbacks, one of which is how rain water is returned to the atmosphere via evaporation. In addition, any better understanding of transpiration losses by vegetation can aid impacts planning of viable crops for future perturbations to the climate system.

Despite this need, many land surface descriptions within climate models contain only an empirical semi-linear response to soil stress. This varies from no effect at a critical moisture level, down to complete shut-down at a prescribed soil moisture wilting point.

Detailed laboratory and field measurements of ABA concentration at the leaf level reveal a strong dependence on both soil moisture and the actual transpiration rate. Concentration levels then influence the amount to which stomata open. This allows the opportunity of building more accurate, chemically-based descriptions into the functioning of the terrestrial part of climate models, with performance verifiable against ecological data. Hence the first role of the paper is to describe the equations in full, and in that context.

Figure 2 of the paper, providing a schematic of the main equations analysed
At the same time, where climate models frequently do excel is in non-water stressed representation of photosynthetic response, including the impact of temperature and light effects. But these descriptions are not included in models of ABA control on stomata, giving the opportunity to merge both. We are not the first to suggest this (see earlier paper, Dewar, 2002) but here, as we unite equation sets, we fully analyse their projections of such a common model to soil moisture, light, temperature, CO2 concentration and surface humidity – our Figure 1 within the paper. This can be important to check as such linking can create odd cross-effects between model components. Fortunately we find this more ABA-based combined model does reproduce the salient features of expected stomata response across a range of imposed environmental conditions. We offer this as a possible future candidate for inclusion in climate models.

There is, however, also a mathematical surprise!

Despite our linking together in a common framework, which generally makes models more complex, we find that equation re-arrangement may actually simplify things. Stomatal response can be re-written as a function of soil moisture, evaporative flux, atmospheric CO2 concentration and photosynthetic flux only. We are not suggesting that this is necessarily what the stomata “see” to guide their responses (eg with drivers such as temperature occurring instead of via influence on photosynthesis). But the ability to write the equations in this form links to a long-term “store” of the hydrological cycle, ie soil moisture, and to a more instantaneous flux, ie transpiration, the latter fluctuating more with weather conditions.  And, in a symmetry for the carbon cycle, links to the “store” of atmospheric CO2 concentration, and again to more immediate fluctuations of photosynthetic uptake.

Could plants therefore respond to the more slowly changing stores in the carbon and water cycles, but using fluxes to provide time-evolving corrections dependent on the precise passing meteorological conditions?

Although our priority is to try and contribute towards improving process representation in land surface models, we really hope that other authors might investigate further the “stores-fluxes” concept that the equations of this model hint at.”

Dr Chris Huntingford

Additional links

Chris Huntingford, D Mark Smith, William J Davies, Richard Falk, Stephen Sitch, Lina M Mercado. Combining the [ABA] and net photosynthesis-based model equations of stomatal conductance. 2015. Ecological Modelling. doi: 10.1016/j.ecolmodel.2015.01.005

The full paper is open access and can be read by anyone. The work was carried out by scientists from CEH, Exeter University, Lancaster University and the IUCN.

Staff page of Dr Chris Huntingford

CEH Climate science referenced in US Senate

Earlier this year a climate modelling paper published in Nature in 2013 which was led by CEH scientist Dr Chris Huntingford was mentioned in a US Senate debate.

Senator James M Inhofe made reference to the research during a debate on the KXL oil pipeline. He was reported as claiming that the Huntingford Nature paper casts doubt on the reality of anthropogenic climate change.

His exact words were "Nature journal, which is a well-respected journal, in their 2013 paper said that 'there is considerable uncertainty as to whether [increases in extreme climate variability] is occurring."

Subsequent to the debate Dr Huntingford was contacted by a US journalist and asked if his research did show there is "considerable uncertainty as to whether [increases in extreme climate variability] is occurring."

Chris replied, "Our Nature paper strictly analyses only year-to-year variability (fluctuations) in temperature, and demonstrates that in some parts of the world, this is actually going down. Elsewhere it is going up. This may be seen in both direct measurements and in supporting climate model simulations. This goes against the view that maybe, as general global warming occurs, everywhere will additionally see larger year-to-year swings in temperature."

"However, we do not at any point offer evidence against a general on-going background and upwards warming trend. Detection and attribution statistical studies show that the observed average increasing temperatures are almost certainly a consequence of the burning of fossil fuels."

This quote was used verbatim here and has also been subsequently referred to in the Congressional Record (Proceedings and debates of the US Congress).

You can read more about the original paper on the CEH website here.

One year on: reviewing the floods of 2013/2014

This month’s issue of Weather, the journal of the Royal Meteorological Society, takes a look back at last winter, asking “How unusual were the storms and floods experienced by many areas of the UK during late 2013 and early 2014?”

As well as papers on the weather systems (Kendon and McCarthy) and coastal flooding (Sibley et al), Katie Muchan from CEH together with colleagues Jamie Hannaford and Simon Parry, and Melinda Lewis of the British Geological Survey, review the inland flooding, which included prolonged river flooding in many areas – notably on the Somerset Levels and in the Thames Valley – and the opening of a large number of sinkholes, bringing damage to property and affecting livelihoods.

Walking through flood water. Photo: Julia Lawrence

In the paper, Katie and her colleagues outline several key aspects of the events of last winter, concluding:
“A defining aspect of the winter was the occurrence of multiple types of flooding. The combination of coastal, pluvial, fluvial and groundwater flooding in winter is not unusual, but its extent, frequency and severity through the winter of 2013/2014 was extraordinary.” 

They add, “The simultaneous occurrence of multiple types of flooding and other weather hazards presented a major challenge for the emergency services.”

Data from the National Hydrological Monitoring Programme (NHMP) forms the source of much of the material discussed in the Muchan et al paper.

Average winter outflows (m3s-1) for Great Britain 1961-2013

The NHMP, mentioned on many previous occasions in this blog, collates data for 104 index river flow gauging stations and 37 index groundwater boreholes in the UK, and produces monthly Hydrological Summaries.

Related links

Full citation for the paper: Muchan K, Lewis M, Hannaford J & Parry S (2015) The winter storms of 2013/2014 in the UK: hydrological responses and impacts, Weather, 70(2), 55-61. It is open access.

Weather, Special Issue: The storms of winter 2013/2014 in the UK 

Monthly Hydrological Summaries for the UK

More on the NHMP: Rainfall, UK floods and the potential impacts of climate change? 6 January 2014