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Concerns exist about the viability of food security across Europe due to multiple, potentially adverse drivers. These include economic, political and climate forcing factors, all of which require quantification. Here, we focus on the climate forcing, and in particular, the soil moisture change component which crucially determines water availability for crop uptake. We estimate future soil moisture levels at 34 sites of the UK COsmic-ray Soil Moisture Observing System (COSMOS-UK) network. We do this by combining three platforms: the Joint UK Land Environment Simulator (JULES) land surface model, field-scale soil moisture observations from the COSMOS-UK stations and 2.2 km convection-permitting UK Climate Projections (UKCP18). We use COSMOS-UK data to optimise key soil moisture-related parameters in the JULES model, based on its performance in the contemporary period. We then force the calibrated model with UKCP18 data to produce future soil moisture estimates. We evaluate the modelled soil moisture for an average soil depth between 0 and 35 cm to match the depth of soil moisture observations. Our main conclusions concern future soil moisture droughts which we compare with equivalent events in the historical period, 1982-2000. We find that on average across all sites, there is an increase in the frequency of future extreme soil moisture drought events of duration above 90 days. In 2062-2080, such frequency increase of between 0.1 and 0.6 events per year (equivalent to at least 2 and up to 12 additional events in a 20-year period) is expected. We also show that, in 2062-2080, there is an increased risk of high or more intense soil moisture drought conditions in months between May and November, with months between June and October being at especially high risk. The UKCP18 data corresponds to a high-emissions future described by the RCP8.5 scenario.

Chapter 2. Whilst infrastructure projects have often focused on improving the supply of water for agriculture, there has been much less focus on managing or reducing the agricultural water demand. The net effect of increasing supply, without managing demand, is that agricultural water (and energy) consumption increases, without necessarily increasing food production. Improved agricultural Water Use Efficiency (WUE) can help address this issue, as well as contributing to reducing the pressures on water resources (NITI Aayog 2019). This chapter outlines how recent improvements in large area measurement of soil moisture and the availability of high-resolution Soil Moisture Deficit information at a fine scale can provide actionable guidance to farmers. Practical methods, demonstrated in farm pilot studies, to manage irrigation demand are discussed, along with considerations of efficient irrigation methods, with the objective of improving WUE.

Potential land–climate feedbacks in subarctic regions, where rapid warming is driving forest expansion into the tundra, may be mediated by differences in transpiration of different plant functional types. Here, we assess the environmental controls of overstorey transpiration and its relevance for ecosystem evapotranspiration in subarctic deciduous woodlands. We measured overstorey transpiration of mountain birch canopies and ecosystem evapotranspiration in two locations in northern Fennoscandia, having dense (Abisko) and sparse (Kevo) overstories. For Kevo, we also upscale chamber‐measured understorey evapotranspiration from shrubs and lichen using a detailed land cover map. Subdaily evaporative fluxes were not affected by soil moisture and showed similar controls by vapour pressure deficit and radiation across sites. At the daily timescale, increases in evaporative demand led to proportionally higher contributions of overstorey transpiration to ecosystem evapotranspiration. For the entire growing season, the overstorey transpired 33% of ecosystem evapotranspiration in Abisko and only 16% in Kevo. At this latter site, the understorey had a higher leaf area index and contributed more to ecosystem evapotranspiration compared with the overstorey birch canopy. In Abisko, growing season evapotranspiration was 27% higher than precipitation, consistent with a gradual soil moisture depletion over the summer. Our results show that overstorey canopy transpiration in subarctic deciduous woodlands is not the dominant evaporative flux. However, given the observed environmental sensitivity of evapotranspiration components, the role of deciduous trees in driving ecosystem evapotranspiration may increase with the predicted increases in tree cover and evaporative demand across subarctic regions.

A new network of eddy covariance (EC) stations was established at a variety of semi-natural and managed ecosystems located across India during the INCOMPASS project. These new stations were installed to monitor surface-atmosphere fluxes of water, energy and carbon dioxide (CO2) and to provide supporting micrometeorological and soil physics observations. In this presentation, EC flux observations obtained at a semi-natural Phragmites-Saccharum-Imperata grassland on the Indo-Gangetic Plain are presented. The poster presents flux observations captured over two complete annual cycles. The grassland was characterised by a distinct seasonality. Latent heat dominated the turbulent energy flux during Monsoon, whereas sensible heat was the dominant turbulent flux during winter. The site experienced periodic flooding by waters from an adjacent irrigation canal as well as the removal of aboveground biomass during a wildfire in May 2017. Additional flood waters did not have a large influence on turbulent energy fluxes during inundation periods. Wildfire influenced fluxes in the period after the burn. Latent heat and net carbon gain recovered to pre-disturbance levels within a month of the wildfire.

Extrapolating biosphere-atmosphere CO2 flux observations to larger scales in space, part of the so-called “upscaling” problem, is a central challenge for surface-atmosphere exchange research. Upscaling CO2 flux in tundra is complicated by the pronounced spatial variability of vegetation cover. We demonstrate that a simple model based on chamber observations with a pan-Arctic parameterization accurately describes up to 75% of the observed temporal variability of eddy covariance—measured net ecosystem exchange (NEE) during the growing season in an Abisko, Sweden, subarctic tundra ecosystem, and differed from NEE observations by less than 4% for the month of June. These results contrast with previous studies that found a 60% discrepancy between upscaled chamber and eddy covariance NEE sums. Sampling an aircraft-measured normalized difference vegetation index (NDVI) map for leaf area index (L) estimates using a dynamic flux footprint model explained less of the variability of NEE across the late June to mid-September period, but resulted in a lower root mean squared error and better replicated large flux events. Findings suggest that ecosystem structure via L is a critical input for modeling CO2 flux in tundra during the growing season. Future research should focus on quantifying microclimate, namely photosynthetically active radiation and air temperature, as well as ecosystem structure via L, to accurately model growing season tundra CO2 flux at chamber and plot scales.

Clifford (1971) derived expressions for the real and imaginary part of the temporal spectra W(f) for spherical waves propagating through the atmosphere. To a good approximation, the transmitter of a Millimeter-Wave Scintillometer (MWS) can be regarded as a point source and thus Clifford's theory is applicable to a MWS. Nieveen et al. (1998) extended Clifford's theory to large aperture scintillometers (LAS). In both cases a so called corner frequency, fc , can be defined. For frequencies smaller than fc , the real part of W(f) is approximately constant at Wplateau, whereas for f>fc , the real part of W(f) is proportional to f-8/3 for the MWS. It is noted that Wplateau is inversely proportional to the cross wind uc and that fc is proportional to uc, therefore the integral of W(f) over all f is independent of uc; however, this applies for the case where the cross wind does not vary along the path. During a field experiment carried out in mid-summer 2006 at Sheepdrove Organic Farm, UK, over mixed agricultural land use and complex topography, W(f) was measured by a 94 GHz MWS. There were contrasting cool-windy and hot-convective weather conditions during the experiment. With these data the Clifford theory will be validated.

Cosmic Ray Neutron Probes (CRNP) have found application in soil moisture estimation due to their conveniently large (>100 m) footprints. Here we explore the possibility of using high density polyethylene (HDPE) moderator to limit the field of view, and hence the footprint, of a soil moisture sensor formed of 12 CRNP mounted on to a mobile robotic platform (Thorvald) for better in-field localisation of moisture variation. URANOS neutron scattering simulations are used to show that 5 cm of additional HDPE moderator (used to shield the upper surface and sides of the detector) is sufficient to (i), reduce the footprint of the detector considerably, (ii) approximately double the percentage of neutrons detected from within 5 m of the detector, and (iii), does not affect the shape of the curve used to convert neutron counts into soil moisture. Simulation and rover measurements for a transect crossing between grass and concrete additionally suggest that (iv), soil moisture changes can be sensed over a length scales of tens of meters or less (roughly an order of magnitude smaller than commonly used footprint distances), and (v), the additional moderator does not reduce the detected neutron count rate (and hence increase noise) as much as might be expected given the extent of the additional moderator. The detector with additional HDPE moderator was also used to conduct measurements on a stubble field over three weeks to test the rover system in measuring spatial and temporal soil moisture variation.