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

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

Urbanisation impacts on storm runoff along a rural-urban gradient

Urbanisation alters the hydrological response of catchments to storm events and spatial measures of urban extent and imperviousness are routinely used in hydrological modelling and attribution of runoff response to land use changes. This study evaluates whether a measure of catchment urban extent can account for differences in runoff generation from storm events along an rural-urban gradient. We employed a high-resolution monitoring network across 8 catchments in the south of the UK - ranging from predominantly rural to heavily urbanised - over a four year period, and from this selected 336 storm events. Hydrological response was compared using volume- and scaled time-based hydrograph metrics within a statistical framework that considered the effect of antecedent soil moisture. Clear differences were found between rural and urban catchments, however above a certain threshold of urban extent runoff volume was relatively unaffected by changes and runoff response times were highly variable between catchments due to additional hydraulic controls. Results indicate a spatial measure of urbanisation can generally explain differences in the hydrological response between rural and urban catchments but is insufficient to explain differences between urban catchments along an urban gradient. Antecedent soil moisture alters the volume and timing of runoff generated in catchments with large rural areas, but was not found to affect the runoff response where developed areas are much greater. The results of this study suggest some generalised relationships between urbanisation and storm runoff are not represented in observed storm events and point to limitations in using a simplified representations of the urban environment for attribution of storm runoff in small urban catchments. The study points to the need for enhanced hydrologically relevant catchment descriptors specific to small urban catchments and more focused research on the role of urban soils and soil moisture in storm runoff generation in mixed land-use catchments

High level review of the Optimum Water Use methodology for agriculture following the 2018 drought in England

1. Context. After a spate of relatively average to ‘wet’ summers in England from an irrigation perspective, the heatwave and protracted dry conditions in 2018 highlighted the significant agronomic and economic importance of water resources for agricultural irrigation and the risks to production that can arise when abstractions are restricted. From an abstraction licensing perspective (licensed volume and reasonable need) 2018 also provides a useful ‘reference’ year against which actual irrigation applications (depths applied) can be compared against theoretical ‘design’ dry year requirements. It also offers an opportunity to gather feedback from abstractors on their management practices, how they coped with the drought conditions and any lessons learnt in order to support the EA in providing abstractor guidance to support improved decision-making in future drought years. Following discussion with EA staff, this short study was commissioned to produce a Technical Briefing Note for the irrigated agriculture sector in England ahead of the 2019 spray irrigation season. The intention was that the report would include a brief agroclimatic assessment of 2018 and provide additional information to complement the EA Spray Irrigation (SI) Prospects Information which is distributed to abstractors each year. This Technical Briefing Note summarises the aim and objectives of the study, the methodological approaches developed and the key findings that emerged from the analyses

The exposure of a fresh fruit and vegetable supply chain to global water-related risks

We have combined estimates of the UK’s supply of fresh fruit and vegetables (1996 – 2015) with estimates of water requirements and water scarcity in producing countries, to identify where the supply is exposed to physical, regulatory and reputational water risks and how this has changed over time. Some 76% of the freshwater consumed in the supply of fresh fruit and vegetables to the UK is withdrawn overseas. The supply chain is particularly exposed to water risks in Spain, Egypt, South Africa, Chile, Morocco, Israel and Peru. Exposure has increased over time

Reusing oil and gas produced water for irrigation of food crops in drylands

Water scarcity severely affects drylands threatening their food security, whereas, the oil and gas industry produces significant and increasing volumes of produced water that could be partly reused for agricultural irrigation in these regions. In this review, we summarise recent research and provide a broad overview of the potential for oil and gas produced water to irrigate food crops in drylands. The quality of produced water is often a limiting factor for the reuse in irrigation as it can lead to soil salinisation and sodification. Although the inappropriate use of produced water in irrigation could be damaging for the soil, the agricultural sector in dry areas is often prone to challenges in soil salinity. There is a lack of knowledge about the main environmental and economic conditions that could encourage or limit the development of irrigation with oil and gas effluents at the scale of drylands in the world. Cheaper treatment technologies in combination with farm-based salinity management techniques could make the reuse of produced water relevant to irrigate high value-crops in hyper-arid areas. This review paper approaches an aspect of the energy-water-food nexus: the opportunities and challenges behind the reuse of abundant oil and gas effluents for irrigation in hydrocarbon-rich but water-scarce and food-unsecured drylands

Understanding the impact of crop and food production on the water environment ‐using sugar as a model

The availability of fresh water and the quality of aquatic ecosystems are important global concerns, and agriculture plays a major role. Consumers and manufacturers are increasingly sensitive to sustainability issues related to processed food products and drinks. The present study examines the production of sugar from the growing cycle through to processing to the factory gate, and identifies the potential impacts on water scarcity and quality and the ways in which the impact of water use can be minimised. We have reviewed the production phases and processing steps, and how calculations of water use can be complicated, or in some cases how assessments can be relatively straightforward. Finally, we outline several ways that growers and sugar processors are improving the efficiency of water use and reducing environmental impact, and where further advances can be made. This provides a template for the assessment of other crops

Using variograms to detect and attribute hydrological change

There have been many published studies aiming to identify temporal changes in river flow time series, most of which use monotonic trend tests such as the Mann–Kendall test. Although robust to both the distribution of the data and incomplete records, these tests have important limitations and provide no information as to whether a change in variability mirrors a change in magnitude. This study develops a new method for detecting periods of change in a river flow time series, using temporally shifting variograms (TSVs) based on applying variograms to moving windows in a time series and comparing these to the long-term average variogram, which characterises the temporal dependence structure in the river flow time series. Variogram properties in each moving window can also be related to potential meteorological drivers. The method is applied to 91 UK catchments which were chosen to have minimal anthropogenic influences and good quality data between 1980 and 2012 inclusive. Each of the four variogram parameters (range, sill and two measures of semi-variance) characterise different aspects of the river flow regime, and have a different relationship with the precipitation characteristics. Three variogram parameters (the sill and the two measures of semi-variance) are related to variability (either day-to-day or over the time series) and have the largest correlations with indicators describing the magnitude and variability of precipitation. The fourth (the range) is dependent on the relationship between the river flow on successive days and is most correlated with the length of wet and dry periods. Two prominent periods of change were identified: 1995–2001 and 2004–2012. The first period of change is attributed to an increase in the magnitude of rainfall whilst the second period is attributed to an increase in variability of the rainfall. The study demonstrates that variograms have considerable potential for application in the detection and attribution of temporal variability and change in hydrological systems

Poor encoding of position by contrast-defined motion

Second-order (contrast-defined) motion stimuli lead to poor performance on a number of tasks, including discriminating form from motion and visual search. To investigate this deficiency, we tested the ability of human observers to monitor multiple regions for motion, to code the relative positions of shapes defined by motion, and to simultaneously encode motion direction and location. Performance with shapes from contrast-defined motion was compared with that obtained from luminance-defined (first-order) stimuli. When the position of coherent motion was uncertain, direction-discrimination thresholds were elevated similarly for both luminance-defined and contrast-defined motion, compared to when the stimulus location was known. The motion of both luminance- and contrast-defined structure can be monitored in multiple visual field locations. Only under conditions that greatly advantaged contrast-defined motion, were observers able to discriminate the positional offset of shapes defined by either type of motion. When shapes from contrast-defined and luminance-defined motion were presented under comparable conditions, the positional accuracy of contrast-defined motion was found to be poorer than its luminance-defined counterpart. These results may explain some, but possibly not all, of the deficits found previously with second-order motion

The impact of changing food choices on the blue water scarcity footprint and greenhouse gas emissions of the British diet: The example of potato, pasta and rice

Food production is a major contributor to a country's environmental burden. However, the burdens associated with individual foods vary significantly due to differing agricultural systems and locations, post-harvest storage, manufacturing and transport requirements. Dietary choices can therefore have a significant impact on the overall burdens associated with food consumption. Previous studies have generally considered changes in the proportion of animal-based foods in the diet or changes to a vegetarian, or a vegan diet. Using a life cycle assessment approach and data from published sources supplemented by original analysis, we estimated the blue water scarcity footprint and greenhouse gas emissions associated with the production, manufacture and distribution of three popular starchy carbohydrate foods as consumed in the United Kingdom – British fresh potatoes, Italian dried pasta and Indian dried basmati rice. Although similar to pasta in terms of greenhouse gas emissions per unit carbohydrate, when considered on the basis of typical portion size, potatoes have lower greenhouse gas emissions than pasta or basmati and the blue water scarcity footprint of basmati is two orders of magnitude greater than potatoes or pasta. The increasing preference for pasta and rice and reduction in household purchases of fresh potatoes in the United Kingdom over the period 1981–2010 has resulted in an increase in blue water scarcity footprint and a transfer of burdens from the United Kingdom to Italy and India, however the increased greenhouse gas emissions associated with rice and pasta has been, more or less, compensated by a reduction in emissions associated with purchases of potatoes. This paper has shown that dietary choices within food groups (in this case starchy carbohydrates) have a significant impact on an individual's contribution to greenhouse gas emissions and blue water scarcity footprint. The life cycle assessment approach is useful for understanding where the impacts of dietary choices occur and can inform the supply chain about where efforts should be targeted to reduce those impacts