CERES :: Browsing by Author "Hess, Tim M."

Browsing by Author "Hess, Tim M."

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Open Access
Accumulation, transport and potential treatment of surface sediment on car parks with channel drains
(Cranfield University, 2015-11) Barlow, James Vincent; Harris, Jim A.; Hess, Tim M.
Urban pollutants have been identified as a significant source of environmental pollution, posing a risk to human health, the environment, and are toxic to flora and fauna. Highways are recognised as one of the key sources of pollution, from both vehicles, and surrounding infrastructure. A number of studies have investigated accumulation of sediment and the associated pollutants on highways, and the runoff generated as a result of rainfall. Car parks share many potential contributory sources of pollutants with highways, but there is a lack of studies regarding car parks, despite them being identified as a significant percentage of urban land use. A series of experiments were undertaken in order to develop an understanding of the characteristics of car park sediment. The physical and chemical characteristics of sediment were analysed at different stages throughout the drainage system. Firstly on the sediment accumulated on car park surfaces, followed by that mobilised and transported into a channel drain during simulated rainfall events. Finally, potential treatment of pollutants within sediment in a channel was quantified. The physical and chemical characteristics of car park sediment was shown to be similar during both the accumulation (build-up) and wash-off stages, suggesting that the accumulated sediment is generally mobilised and transported to the channel drain (wash-off). Furthermore, both the physical and chemical characteristics of the sediment were shown to be similar to those found on highways, thorough the build-up and wash-off phases. Finally, potential treatment of organic pollutants (PAH) by biodegradation was demonstrated, but not comprehensively proved.
Open Access
Agro-environmental sustainability and financial cost of reusing gasfield-produced water for agricultural irrigation
(Elsevier, 2019-10-29) Alban, Echchelh; Hess, Tim M.; Sakrabani, Ruben
Produced water (PW) is the largest by-product generated from oil and gas extraction. Currently, half of the total PW volume is managed through environmentally-controverted and costly disposal practices. In dry regions, PW could be beneficially reused to irrigate crops reducing the overexploitation of freshwater resources. However, PW quality, and particularly its high salinity, sodicity and alkalinity, create uncertainties regarding the agro-environmental sustainability and the cost of this practice. The aim of this paper was to identify potential agro-environmentally sustainable irrigation schemes with gasfield-PW in hyper-arid Qatar and to estimate their operating costs. A soil-water model was used to simulate the irrigation of sugar beet with gasfield-PW under the climatic and soil conditions occurring in northern Qatar. Different irrigation strategies combining over-irrigation, PW blending with treated sewage effluent (TSE) and PW desalination were tested in order to protect the soil and the aquifer from salinisation and sodification. The operating costs of identified agro-environmentally sustainable scenarios were estimated through a cost analysis. In the case study, the simulations indicated that using an irrigation volume up to ∼300% of the crop water needs with a blend of two-thirds PW and one-third TSE (or desalinated PW) could preserve the soil stability, crop yield and groundwater quality. The least-cost option was to reduce the irrigation amount at a little over the crop water needs and mix PW with an equivalent volume of TSE or four equivalent volumes of desalinated PW which would cost $0.26/m3 and $0.46/m3 respectively. As traditional PW disposal practices cost between $0.06–$16.67/m3, reusing PW in irrigation is thus potentially a competitive PW management strategy for O&G firms.
Open Access
Application of integrated models to assess the impacts of floodplain connectivity on ecosystem services: a case study at Tempsford, UK
(Cranfield University, 2015-09) Taktikos, Niko; Hess, Tim M.; Gill, A. B.
Floodplains in the United Kingdom have evolved from natural landscapes to artificially modified ecosystems through managing lateral and vertical floodplain connectivity leading to synergy or trade-offs in ecosystem service delivery. Research methods have been limited in understanding the processes by which ecosystem service values are formed and the data required to support ecosystem service assessment. Developing a methodology while complex and challenging is necessary in order to take the ecosystem approach forward to support decision making for policy makers, planners and stakeholders. The aim of this research was to develop a method to assess the delivery of ecosystem services in response to changes in floodplain connectivity and evaluate the performance. A case study floodplain was selected at Tempsford, downstream of the River Ivel in Bedfordshire, United Kingdom as an example for opportunities to deliver multiple ecosystem services. A sequential integrated modelling system was applied utilising a linked ISIS 1D-2D hydrodynamic model and WaSim, a 1D soil water balance model to simulate changes in floodplain connectivity and generate model data to improve estimates of ecosystem services indicators. A non- monetary multi-criteria analysis methodology was applied to further develop indicators for ecosystem services assessment and to assess the impacts of the model scenarios on ecosystem services delivery. The integration of the WaSim model was unsuccessful as the model performed poorly in the calibration and validation process and was not fit for its intended purpose. It was deduced that potential groundwater seepage in the regional aquifer occurs outside of the field study site, which cannot be modelled in WaSim. To demonstrate the impact of lateral connectivity controls on the water table position, an empirical method was developed using the mean observed water table position to represent a ‘no drainage system’ vertical connectivity scenario. The results showed that in low frequency/high magnitude flood events, increasing the lateral connectivity by lowering embankments provides synergy and benefits to flood alleviation, water supply and freshwater fish habitat and trade-offs and disbenefits to flood damage, agricultural productivity, terrestrial habitat and recreation. In high frequency/low magnitude flood events, decreasing the lateral connectivity by raising embankments still provides the same synergy and trade-offs yet lower benefits and disbenefits. Marginally decreasing the lateral connectivity creates a higher level of benefits and a lower level of disbenefits to promote multi-functional land use in the floodplain. Managing the control of floodplain connectivity needs to be carefully planned to enable multifunctional land use in a floodplain.
Open Access
Assessing future drought risks and wheat yield losses in England
(Elsevier, 2020-11-24) Clarke, D.; Hess, Tim M.; Haro Monteagudo, David; Semenov, Mikhail M.; Knox, Jerry W.
Droughts pose a major risk to agricultural production. By comparing the outputs from an ecophysiological crop model (Sirius) with four drought severity indicators (DSI), a comparative assessment of the impacts of drought risk on wheat yield losses has been evaluated under current (baseline) and two future climate scenarios. The rationale was to better understand the relative merits and limitations of each approach from the perspective of quantifying agricultural drought impacts on crop productivity. Modelled yield losses were regressed against the highest correlated variant for each DSI. A cumulative distribution function of yield loss for each scenario (baseline, near and far future) was calculated as a function of the best fitting DSI (SPEI-5July) and with the equivalent outputs from the Sirius model. Comparative analysis between the two approaches highlighted large differences in estimated yield loss attributed to drought, both in terms of magnitude and direction of change, for both the baseline and future scenario. For the baseline, the average year differences were large (0.25 t ha−1 and 1.4 t ha−1 for the DSI and Sirius approaches, respectively). However, for the dry year, baseline differences were substantial (0.7 t ha−1 and 2.7 t ha−1). For the DSI approach, future yield losses increased up to 1.25 t ha−1 and 2.8 t ha−1 (for average and dry years, respectively). In contrast, the Sirius modelling showed a reduction in future average yield loss, down from a baseline 1.4 t ha−1 to 1.0 t ha−1, and a marginal reduction for a future dry year from a baseline of 2.7 t ha−1 down to 2.6 t ha−1. The comparison highlighted the risks in adopting a DSI response function approach, particularly for estimating future drought related yield losses, where changing crop calendars and the impacts of CO2 fertilisation on yield are not incorporated. The challenge lies in integrating knowledge from DSIs to understand the onset, extent and severity of an agricultural drought with ecophysiological crop modelling to understand the yield responses and water use relations with respect to changing soil moisture conditions.
Open Access
Assessing the impacts of drought on UK wheat production
(Cranfield University, 2017-01) Clarke, David; Knox, Jerry W.; Hess, Tim M.
Water limitations typically reduce UK wheat yields on average by 1-2 t ha- 1 , although this can be considerably more in extreme drought years. With the frequency and intensity of droughts expected to increase under a changing climate, an improved understanding of the impacts of drought and better systems for agricultural drought monitoring are required. Previous studies, however, have found no significant relationship between UK wheat yields and commonly employed drought severity indices (DSI). Using historical (1911-2015) daily weather data for Cambridge the Standardized Precipitation Index (SPI), the Standardized Precipitation and Evapotranspiration Index (SPEI), the Palmer Drought Severity Index (PDSI) and the Potential Soil Moisture Deficit (PSMD) were calculated on various time steps (e.g. 1-12 months for SPI and SPEI) to provide a drought record for the site. A wheat crop growth simulation model (Sirius) was then used to simulate the effects of the identified historic droughts on wheat yields. The use of the Sirius crop model removed the non-drought related yield losses (e.g. disease, pests, and lodging) present in national yield records. Using the Spearman’s Rho correlation coefficient (r) the simulated yield record was then correlated against the different DSIs. The droughts of 1921, 1976 and 2010 were found to be the most extreme in term of yield reduction. In addition, there were also two noticeable periods of successive yield loss in the early 1940s and between 2009 and 2013. All DSIs showed significant (p = 0.05) correlations on monthly time steps between April and August. The SPI, SPEI and PSMD showed a strong correlation to wheat yields (r = 0.64 to 0.66) on time steps incorporating the end of the ‘construction’ and the entirety of the ‘production’ phases for wheat growth. The PDSI showed the weakest correlation (r = 0.55), although it may be helpful in identifying yield-limiting droughts earlier in the year. The research has contributed new scientific insights and understanding of the impacts of historic droughts on wheat productivity, and demonstrated the application of DSIs in monitoring potentially yield-limiting droughts. The research also provides new evidence to support developments in UK food security and drought management for agriculture.
Open Access
Characterising urban catchments for explaining storm runoff and application in UK flood estimation
(2019-02) Miller, James; Brewer, Timothy R.; Hess, Tim M.
The impacts of urbanisation on catchment hydrology have been the focus of investigation over the last few decades, but quantifying and predicting the impacts remains an ongoing area of active research. One such area has been improving characterisation of urban land cover to predict urbanisation impacts whereby lumped catchment characterisation of urban land cover limits the ability of attribution and modelling methods to consider the spatial role of land cover in runoff response. This thesis evaluates the potential for spatially explicit characterisations of urban land cover based on landscape metrics, commonly employed in landscape ecology, to explain storm runoff in urban catchments and their application in UK flood estimation methods. Rainfall and channel flow monitoring across two towns containing 18 variably urbanised sub-catchments were used to provide high-resolution time-series of rainfall and runoff and to identify storm events which were quantified using a range of hydrological metrics. Analysing storm runoff along a rural-urban gradient showed a lumped measure of urban extent can generally explain differences in the hydrological response between rural and urban catchments but not between more urbanised catchments in which soil moisture does not play a contributing role. Using high resolution geospatial data can improve the representation of the urban environment and landscape metrics can better represent the form and function of urban land cover, improving estimates of the index flood QMED over lumped catchment descriptors. Regression analysis of hydrological metrics showed the potential of landscape metrics for explaining inter-catchment differences in rainfall-runoff and point to the importance of considering the location and connectivity of urban surfaces. Landscape metrics provide a workable means of overcoming the limitations inherent in using lumped characterisation of complex urban land cover and their ability to express connectivity, size and location of urban land cover promises potential applications in hydrological applications such as UK design flood estimation methods.
Open Access
Development and application of runoff model for ater harvesting in North East Nigeria.
(1999-12) Audu, Idriss; Hess, Tim M.
Rainfall in the northeast arid zone of Nigeria is limited and has been found to be declining over the last three decades (Hess et al., 1995). This problem of inadequate rainfall is further exacerbated by runoff especially on the degraded lands (fako). Such runoff-prone lands are potential areas for water harvesting. In dry years, harvested runoff water can considerably improve the environmental conditions for plant growth and can make the difference between death and survival. However, water conservation techniques will only show a benefit if the soil is able to hold the extra water within the root zone of the crops. A clear understanding of soil properties and moisture variations on these lands should provide the baseline information needed for applied soil and water management research. Aerial photographs and photo mosaics were used to identify several fako lands out of which three sites were selected for detailed study. The three sites were located at Jawa (12° 48.71’ N, 11° 02.21* E), Zurkaya (12° 49.15’ N, 11° 05.52’ E) and along Dumburi road (12° 54.31!N, 11° 07.49!E). The fako lands have compacted loamy and clay loamy soils with low infiltration rate and hydraulic conductivity. Dry bulk density values range between 1.34 gem¯³ to 1.61 gem¯³ and saturated hydraulic conductivity obtained were between 1 mm/h and 6 mm/h. Water retention characteristic curves revealed that the fako soils have good water holding capacity. Slopes are generally gentle and range from 0.1% to about 1%. Volume of water harvested depends on the runoff yield of an area. Models can be used to estimate runoff on the fako lands. The model to be used will depend upon the available information, the required accuracy and the resolution of the output and the time resources that can be directed at the modelling exercise. As the rainfall data available for the area is in daily time step, a model that can use daily rainfall as input to estimate runoff is required. In order to develop such a model, accurate rainfall-runoff records for several years should be obtained. High-resolution rainfall data for 13 site-years were collected between 1992 and 1994. The EUROSEM model (Morgan et al., 1992) was applied to simulate the rainfall events and partition them into overland flow and infiltrated water. The model was however calibrated and validated before being used for the simulations. For the calibration and validation, a rainfall simulator (USDA, 1972) was constructed and 32 rainfall-runoff events at intensities of between 25 mmh¯¹ and 169 mmh¯¹ were artificially generated on the three sites. A graph of measured versus simulated runoff events showed good agreements in both calibration and validation. Coefficients of determination and efficiency were 0.82 each in calibration and 0.83 and 0.74 in validation. Predicted runoff by the EUROSEM model was regressed against daily rainfall to obtain a linear regression model for predicting runoff from daily rainfall for the fako lands of north-east Nigeria. The model can be regarded as an integral expression of the physiographic and climatic characteristics that govern the relations between rainfall and runoff on the fako areas. Runoff coefficient and threshold value obtained for the area were 0.44 and 16 mm respectively. The linear model was compared to the curve number model and the runoff estimates by both models were similar. The developed linear model was combined with a water balance model, BALANCE (Hess, 1994) and applied to microcatchment water harvesting investigations. The BALANCE model was used to estimate the water balance components for the area. The Ritchie equation in the BALANCE model was calibrated and validated with field data. Measured versus predicted soil moisture plot gave R² values of 0.90 and 0.89 in calibration and validation respectively. Growth of neem tree (Azadirachta indica) on a typical fako land was simulated with different microcatchment sizes in three categories of years (dry, average and wet). Simulation results indicated that augmenting rainfall through runoff water harvesting technique could provide enough water to sustain growth and ensure rapid establishment of the neem tree seedlings. However, due to reduced dry spell some deep percolation may result during the peak of the rainy season (August - mid September) especially in wet years. A microcatchment size of 12m² (basin-runoff area ratio of 1: 2) was found to sustain year round survival of the tree and minimum drainage for all categories of years. Complementary to water harvesting in the conservation measure, effect of three soil cover treatments (bare, perforated polyethylene cover and solid polyethylene cover) on soil evaporation was investigated. As expected, the solid cover was found to have the most effect in reducing soil evaporation but this is not suitable in the current situation because it limits infiltration of rain and free air circulation. The perforated cover treatment is preferred as it can also significantly reduce soil evaporation and at the same time allow unrestricted infiltration of rain and free exchange of gases between the soil and atmosphere.
Open Access
Development of a range of plausible future land use, land management and growing season changes
(2014-06-11) Holman, Ian P.; Hess, Tim M.
This report is part of the "Land use, climate change & water availability (Phase 2a)" project which was commissioned and funded by the Department for Environment, Food and Rural Affairs (Defra). Based on a review of the literature, it describes plausible characteristics of future land use and management changes (induced by climate or social change by the 2050s) that are likely to influence water availability.
Open Access
Drainage benefits and farmer uptake
(Severn Trent Water Authority, 1984-07) Morris, J.; Hess, Tim M.; Ryan, A. M.; Leeds-Harrison, P. B.
As part of the Severn Trent Water Authority's need to improve managerial decision on future projects, post appraisals of completed projects have been instigated. These can involve either a comprehensive review of all aspects or the project or, alternatively, can consider key parameters only. In the case of agricultural land drainage schemes key parameters have been identified as the benefits resulting from schemes and the rate of uptake of these benefits by farmers. The investment of public funds in improved agricultural land drainage is normally justified in terms of the resultant net increase in the value of agricultural production.
Open Access
Ecohydrology of a seasonal wetland in the Rift Valley: ecological characterization of Lake Solai
(Blackwell Publishing Ltd, 2009-09-30T00:00:00Z) De Bock, Tanguy; Kervyn De Meerendré, Baptiste; Hess, Tim M.; Gouder De Beauregard, Anne-Christine
The following research describes through an ecohydrological approach, the first assessment of the ecology of Lake Solai, with a particular emphasis on the vegetation. Lake Solai is located 50 km north of Nakuru in the Rift Valley in Kenya at E36°80′-36°84′ to N00°05′- 00°08′. It is a shallow lake that follows a very peculiar seasonal water regime, and that faces conflicts between agriculture and conservation water users. In the upper catchment, an overview of the agricultural practices was implemented and river water uses were identified to assess river flows. Crops/grassland and woodland/shrubland were the major land uses, covering c. 65% of the catchment. Closer to the lake, vegetation samples were collected around the lake together with samples of environmental factors such as soil and water quality. Thirteen vegetation communities were identified within four main zonations: forest, grassland, river inlet and rocky outcrop. These communities showed abundance, distribution and diversity determined mostly by the human pressures, the flooding periods and the salinity. Cynodon, Cyperus and Sporobolus genera were the most abundant
Open Access
The ecological research needs of business
(Wiley-Blackwell, 2010-04) Armsworth, Paul R.; Armsworth, Anastasia N.; Compton, Natalie; Cottle, Phil; Davies, Ian; Emmett, Bridget A.; Fandrich, Vanessa; Foote, Matthew; Gaston, Kevin J.; Gardiner, Phil; Hess, Tim M.; Hopkins, John; Horsley, Nick; Leaver, Natasha; Maynard, Trevor; Shannon, Delia
Businesses have an unrivalled ability to mobilize human, physical and financial capital, often manage large land holdings, and draw on resources and supply products that impact a wide array of ecosystems. Businesses therefore have the potential to make a substantial contribution to arresting declines in biodiversity and ecosystem services. To realize this potential, businesses require support from researchers in applied ecology to inform how they measure and manage their impacts on, and opportunities presented to them by, biodiversity and ecosystem services.
Open Access
Effect of greenspaces on soil hydrology within urban ecosystems.
(2016-09) Piwuna, Raulatu Munidang; Hess, Tim M.; Burgess, Paul J.
Urban greenspaces provide a regulatory ecosystem service for some of the hydrological processes within urban ecosystems. However, soil hydrological properties can vary with variations in urban vegetation type having an impact on the hydrological balance. This study was carried out to determine the effect of urban vegetation type, species and its management within urban ecosystems to deliver a water regulatory service (with soil moisture content, water infiltration rate, hydraulic conductivity as indicators). The research combines data from field and plot measurement. At the field scale, 78 fragments located in Bedford, Luton and Milton Keynes, UK, over a range of soil textures (clay, clay loam, sandy loam and silty clay loam) were investigated. The vegetation types were categorised as managed grass, managed herbaceous, shrubs, trees over managed grass, trees over unmanaged herbaceous, unmanaged herbaceous and woodland/trees. Infiltration rate was not different for the different vegetation types while unsaturated hydraulic conductivity was greater for the managed grass 308 ± 223 mm d⁻¹ than the unmanaged herbaceous 88 ± 51 mm d⁻¹on sandy loam soil. Experimental treatments at plot scale were investigated. A combination of floristic (3 levels: “no”, “some”, “many”) and structural (3 levels: “short”, “medium”, “tall”) manipulation on each plot and 1 non-manipulated plot, located in Cranfield, UK, on a clay soil. There was no difference in infiltration rate, hydraulic conductivity and soil moisture content related to species richness or plant height. The results of the study show that urban vegetation type, increased species richness, and plant height do not negatively impact infiltration rate, and soil moisture content, while hydraulic conductivity is increased using the managed grass on a sandy loam soil. Therefore, the planting of mixed and species rich and different urban vegetation type is encouraged for its other values in the society.
Open Access
Evaporation in fen wetlands
(Cranfield University, 2011-06) Kelvin, J.; Hess, Tim M.
Wicken Fen represents a remnant of the once extensive peat fenlands of East Anglia, which survived large-scale drainage efforts intended to bring land into agricultural production due to its importance within the local economy and subsequently as a site of interest to scientists. Wicken Fen is managed so as to conserve a variety of habitats lost as a result of drainage and therefore does not represent a truly natural environment. Traditional management practices on Sedge Fen, the largest part of Wicken Fen, involve maintaining a 3 – 4 year harvesting cycle and controlling soil water levels. Previous hydrological studies of Wicken Fen have determined that soil water levels are strongly influenced by precipitation and evapotranspiration. The evaporative flux at Sedge Fen is commonly estimated by using meteorological data within empirical formulae such as the Penman Monteith equation owing to measurement difficulties. Furthermore, there has been little investigation of the evaporative loss from fens within the UK. This study aims to investigate the evaporative loss from Sedge Fen so as to better inform hydrological management and to describe evapotranspiration estimation techniques which may be employed at other fen sites. Eddy covariance measurements demonstrated that evapotranspiration from Sedge Fen was typically less than reference evapotranspiration estimates. Evapotranspiration estimates may be improved by consideration of surface parameters which can be described using meteorological data. Meteorological differences existed between Sedge Fen and the surrounding area, resulting in differing evapotranspiration estimates depending on where data was collected. Evapotranspiration measurements were used within a simple water budget model of Sedge Fen and demonstrated the lateral movement of soil water, a hydrological flux previously assumed to be of little consequence within the hydrological balance of Sedge Fen.
Open Access
Evapotranspiration Estimates for Water Balance Scheduling in the UK
(1996-01-01T00:00:00Z) Hess, Tim M.
This paper compares the use of different methods for estimating reference evapotranspiration (ETo) for irrigation scheduling in the UK. Methods include use of long-term averages, daily weather data and evaporimeters. The results from a single trial in Silsoe in 1996 suggest that, with careful maintenance and measurement, a modified atmometer such as the ETgage, can give estimates of ETo which are close to those obtained using the Penman-Monteith equation.
Open Access
Farmer uptake of drainage benefits a regional study
(Cranfield University, 1987-01) Morris, J.; Black, D. E.; Hess, Tim M.
The commitment of public funds to land drainage improvement such as river flood alleviation and improved arterial systems, has been an important component of agricultural support in Britain. The economic performance of these investments depends on whether private farmers actually exploit the potential benefits afforded. Pre-investment appraisals of agricultural land drainage schemes have been criticised for their arbitrary and optimistic predictions of benefit uptake whilst the great variation in benefit uptake between schemes and farmers has hitherto remained unexplained. More recently, in the face of changes in agricultural policy, pressure on public funds, and competition from other land users, there has been a call for a more consistent and objective method for evaluating public sector land drainage investments (HMSO, 1995).
Open Access
A framework for integrating flood defence and biodiversity in washlands in England
(Jrbm, 2005-01-01T00:00:00Z) Morris, Joe; Hess, Tim M.
Concerns about increased flood risk and loss of biodiversity in lowland areas, coupled with changing priorities in the countryside have drawn attention to the potential contribution that managed washlands can make to improved flood management, habitats and wildlife. Following a review of research literature, a survey of flood managers and conservation officers, and an evaluation of selected case sites in England, a framework to help integrate potential flood management and biodiversity opportunities was constructed. This framework consists of three components, namely: a Hydraulic classification which categorises washlands according to degree of hydraulic control; a Habitat classification which captures attributes of washland hydrology that define the type of existing or potential habitats; and, a Menu of Interventions to “engineer” or manage particular flooding and soil wetness regimes and thereby better exploit habitat potential. Washlands were also categorised by main type of benefit whether this is flood management, conservation, or in the case of integratedwashland, a balance of the two. The advantages of alternative administrative and funding arrangements for washlands, whether land acquisition or annual payment to existing land owners, were also explored. It was concluded that the classification of washland flooding and water level regimes can help to define habitat potential. It can also help to guide hydraulic engineering and management actions that can be taken to realise this potential. Although there is potential synergy between flooding and biodiversity under some flood regimes, biodiversity benefits mainly depend on the management of water regimes following flood events. There is a clear need to “join up” hitherto fragmente
Open Access
Identifying future risks to UK agricultural crop production: Putting climate change in context
(Ip Publishing, 2010-12-01T00:00:00Z) Knox, Jerry W.; Morris, Joe; Hess, Tim M.
Internationally, agriculture is widely regarded as one of the sectors at most risk from a changing climate. This is due to the impact of increased temperatures, reduced rainfall and increased frequency of extreme events, not only in the tropics but also in temperate environments. In the UK, growers also face a range of 'non-climate' risks, which, it is often argued, present a potentially greater and more immediate threat to sustainable food production than climate change. This paper highlights the climate and non-climate impacts on crop production, the adaptation options and the institutional and regulatory barriers to their uptake by farmers. It concludes that there are likely to be both positive impacts (for example, yield gains) and negative impacts (for example, increased water stress). Either way, there will be a need for new investments in adaptive management and technology, including new collaborations between the public and private sectors, to enable UK agriculture to respond to the potential effects of climate change
Open Access
Identifying trade-offs and reconciling competing demands for water - integrating agriculture into a robust decision-making framework
(Wiley, 2018-02-26) Knox, Jerry W.; Haro Monteagudo, David; Hess, Tim M.; Morris, Joe
Increasing demands for water, driven by population growth and socio‐economic development, environmental regulations and future climate uncertainty, are highlighting limitations on water supplies. This water‐energy‐food‐environment nexus is not confined to semi‐arid regions but is emerging as a key business, societal and economic risk in humid and temperate countries, where abundant water supplies and regulation have historically coped with fluctuating demands between industry, power generation, agriculture, domestic supply and the environment. In the UK, irrigation is supplemental to rainfall, consumptive in use and concentrated in the driest years and most resource‐stressed catchments. This paper describes an empirical application of a mixed methods approach to integrate agriculture into a robust decision‐making framework, focusing on a water‐stressed region in England. The approach shows that competing demands between sectors can be reconciled and that potential options or portfolios compatible with multi‐sectoral collaboration and investment can be identified. By combining model outputs to forecast the impacts of climate and socio‐economic change on agricultural demand within a regional water resource simulator, future spatial estimates of demand were derived. A set of search and tracked metrics were used to drive multi‐criteria searches to identify preferred supply and demand management orientated portfolios. The methodological challenges in forecasting agricultural demand, defining acceptable ‘trade‐offs’, managing scale and uncertainty issues and the importance of engendering open dialogue between stakeholders is described. The study provides valuable insights for countries where similar emergent issues regarding conflicts over water demand exist.
Open Access
The impact of climatic variability over the period 1961- 1990 on the soil water balance of upland soils in the North East Arid Zone of Nigeria
(Cranfield University, 1991-12) Hess, Tim M.; Stephens, William
Over the period 1961 – 90 the North East Arid Zone of Nigeria experienced a decline in annual rainfall totals and increased aridity which placed increasing pressure on rain fed, millet-based farming systems. The changes in seasonal rainfall total and distribution have been examined and it has been shown that the rate of decline has been consistent across the region. The decline has been dominated by reduction in the number of rain days during the middle of the rainy season and there is no evidence of a significant change in the length of the growing season. Over the same time period, there has been a small, but significant, increase in mean air temperature which has resulted in a small increase in potential evapotranspiration. Other climatic parameters (vapour pressure, solar radiation and wind speed) appear to have remained stable, although the paucity and dubious quality of much of the historical meteorological data make rigorous statistical analysis difficult. A water balance model (BALANCE) developed by the author, was calibrated for a millet crop grown on a typical sandy loam soil in Maiduguri (Nigeria). The model was necessarily parsimonious, but was shown to perform well when calibrated against observed soil water content. However, the empirical nature and high sensitivity of key parameters relating to bare soil evaporation and drainage mean that it is difficult to parameterise the model by laboratory, or independent field measurements. Applying the calibrated model to daily rainfall and average evapotranspiration data from Nguru (Nigeria) for the period 1961 – 93 showed that, with the exception of extreme drought years, the increased aridity would have had little impact on the viability of traditional millet and millet-cowpea intercropping systems prior to the early 1980s. However, after that date, predicted seasonal millet transpiration, and hence predicted yields, have declined, and long duration cowpea intercrops, which were traditionally matured on residual soil moisture after the millet harvest have had insufficient water. Whilst the BALANCE model has been useful in examining the impact of climatic variability on agro-hydrology, it is not a crop physiological model and the interaction between soil water and crop development is poorly represented. The model cannot, therefore be applied with confidence to investigate the potential yield benefits of physical or agronomic interventions to alleviate the impacts of aridity. Although more complex models exist to do this, they require detailed parameterisation of the crop physiology, which was not possible within the scope of this study.
Open Access
Impact of infield irrigation management by Botswana cabbage farmers on soil salinity
(Cranfield University, Cranfield University at Silsoe, 2006-11-08T14:51:56Z) Molatakgosi, Goitsemodimo; Hess, Tim M.
Some vegetable farmers in the semi- arid Botswana are struggling or closing down their enterprises citing the cost of irrigation and salty water as the problem. Irrigation with water from the salt-laden underground water is known to be the main sources of salts for arid and semi-arid agricultural land. Crops grown in saline environments show symptoms similar to those shown by drought-affected crops hence more irrigation is needed therefore increasing the irrigation cost. Research from other semi arid areas shows that water with high salinity levels can be used for irrigation without increasing soil salinity to values beyond critical levels. A lot of studies have been done which show that the impacts of saline irrigation water depend on the irrigation management. This study therefore aims at recommending infield irrigation management practices to be used by cabbage farmers in Botswana without increase in soil salinity to levels that will affect crop yield. A survey was conducted to identify the infield irrigation management practices presently used by cabbage farmers in Botswana. Rootzone salinity trend due to the identified infield irrigation management was simulated for 20 years using WaSim simulation model. Recommendations on irrigation management practices were made for those soil salinity trends that reached critical levels. It was realised that there are no common infield irrigation management used by farmers. The way farmers manage infield irrigation could not be identified with the factors involved in irrigation scheduling. Infield irrigation management by the farmers contribute to the soil salinity increase in their fields and some of the farmers are already using saline soils. Most farmers are not aware of the saline conditions they are farming on and those who know do not know about the soil salinity measures. The study recommends a need to educate farmers on irrigation under saline environments and also a need for farmers to include soil salinity control in their irrigation planning.