The climate change impact and adaptation simulations from the Agricultural Model Intercomparison and Improvement Project (AgMIP) for wheat provide a unique dataset of multi-model ensemble simulations for 60 representative global locations covering all global wheat mega environments. The multi-model ensemble reported here has been thoroughly benchmarked against a large number of experimental data, including different locations, growing season temperatures, atmospheric CO2 concentration, heat stress scenarios, and their interactions. In this paper, we describe the main characteristics of this global simulation dataset. Detailed cultivar, crop management, and soil datasets were compiled for all locations to drive 32 wheat growth models. The dataset consists of 30-year simulated data including 25 output variables for nine climate scenarios, including Baseline (1980-2010) with 360 or 550 ppm CO2, Baseline +2oC or +4oC with 360 or 550 ppm CO2, a mid-century climate change scenario (RCP8.5, 571 ppm CO2), and 1.5°C (423 ppm CO2) and 2.0oC (487 ppm CO2) warming above the pre-industrial period (HAPPI). This global simulation dataset can be used as a benchmark from a well-tested multi-model ensemble in future analyses of global wheat. Also, resource use efficiency (e.g., for radiation, water, and nitrogen use) and uncertainty analyses under different climate scenarios can be explored at different scales. The DOI for the dataset is 10.5281/zenodo.4027033 (AgMIP-Wheat, 2020), and all the data are available on the data repository of Zenodo (http://doi.org/10.5281/zenodo.4027033). Two scientific publications have been published based on some of these data here.

Efforts to limit global warming to below 2°C in relation to the pre-industrial level are under way, in accordance with the 2015 Paris Agreement. However, most impact research on agriculture to date has focused on impacts of warming >2°C on mean crop yields, and many previous studies did not focus sufficiently on extreme events and yield interannual variability. Here, with the latest climate scenarios from the Half a degree Additional warming, Prognosis and Projected Impacts (HAPPI) project, we evaluated the impacts of the 2015 Paris Agreement range of global warming (1.5 and 2.0°C warming above the pre-industrial period) on global wheat production and local yield variability. A multi-crop and multi-climate model ensemble over a global network of sites developed by the Agricultural Model Intercomparison and Improvement Project (AgMIP) for Wheat was used to represent major rainfed and irrigated wheat cropping systems. Results show that projected global wheat production will change by -2.3% to 7.0% under the 1.5°C scenario and -2.4% to 10.5% under the 2.0°C scenario, compared to a baseline of 1980-2010, when considering changes in local temperature, rainfall, and global atmospheric CO2 concentration, but no changes in management or wheat cultivars. The projected impact on wheat production varies spatially; a larger increase is projected for temperate high rainfall regions than for moderate hot low rainfall and irrigated regions. Grain yields in warmer regions are more likely to be reduced than in cooler regions. Despite mostly positive impacts on global average grain yields, the frequency of extremely low yields (bottom 5 percentile of baseline distribution) and yield inter-annual variability will increase under both warming scenarios for some of the hot growing locations, including locations from the second largest global wheat producer-India, which supplies more than 14% of global wheat. The projected global impact of warming <2°C on wheat production is therefore not evenly distributed and will affect regional food security across the globe as well as food prices and trade.

This paper evaluates the usefulness of the Crop Water Stress Index (CWSI) for monitoring transpiration and water status in almond trees, and proposes a methodology for assessing crop yield derived from the relation between canopy temperature and transpiration. For this purpose, a Non-Water Stress Baseline (NWSB) was developed from canopy temperature measurements taken with Infrared Thermometers (IRT) installed permanently over well-watered trees for three years. Tree transpiration was measured continuously with sap flow probes installed in the same trees than the IRT sensors. The calculated CWSI was closely related to water potential and stomatal conductance measured during kernel filling, as well as with transpiration and the ratio kT/GC (the transpiration coefficient over the ground cover). Taking into consideration this relation and the water production function recently published, the seasonal CWSI was compared to final yield and the regression yielded good results (R-2 = 0.80). An empirical relationship between the CWSI acquired remotely from two flights performed during the kernel filling stage and crop yield was determined for this orchard. The estimated yield from the proposed methodology was compared to ground-truth measurements of crop yield measured in 80 trees during 2014 and 2015. The result obtained a RMSE that yielded 1.54 kg/tree. This study thus demonstrates that CWSI is closely related to the transpiration and the ratio kT/GC. This relation settles the basis for the development of methodologies for estimating water-limited crop yield from thermal derived information.

Accurate methods to determine irrigation requirements are necessary for the efficient use of water in agriculture. We conducted measurements of transpiration (T) of one almond tree placed in a large weighing lysimeter and instrumented with sap-flow probes for three seasons (2014–2016; 6–9 years after transplanting). We also conducted independent T estimations by the water balance method in four plots. Transpiration was related to reference evapotranspiration (ETo) to obtain the coefficient of transpiration (KT = T/ETo). Average mid-season KT of the lysimeter tree was 0.55, 0.68 and 0.91 in 2014, 2015, and 2016, respectively, and maximum ground cover (GC) was 55, 59 and 55% for the same years. These KT values standardized by GC were supported by the independent estimations of KT/GC obtained in the plots using the water balance, except in 2016, when a very high KT value was observed in the lysimeter tree. There were significant fluctuations in daily KT during mid-season, which we found to be related to wind speed. Furthermore, the exceptionally high KT/GC relationship of 2016 was apparently related to the very high crop load in the lysimeter of that year (75% more than the 2 other normal years). Hourly bulk canopy conductance values were derived from lysimeter T records to confirm the high transpiration rates prior to harvest during 2016. From the KT values measured here, we propose that the mid-season KT of fully mature almond orchards, with a GC of 75%, should be around—between 0.9 and 1.05. An estimation of evaporation from soil, which is dependent on the method of irrigation, needs to be added to obtain the net water requirements.

Irrigation optimization under limited water supply requires knowledge of the relation between consumptive use and production. The recent expansion of almond production is highly dependent on irrigation which may be limited by water scarcity in the future. A 3-year experiment was conducted in Cordoba, Spain, to determine the yield and water productivity (WP) responses of almond (cv. Guara) to irrigation deficits. Maximum yields of 2508.4 kg/ha (3-year average) were obtained when the crop evapotranspiration (ETC) was fully met. Three deficit irrigation treatments that supplied 66.9, 69.7 and 43.2% of the full irrigation requirements yielded 2147.5, 2038.2, and 1496.9 kg/ha, respectively. Assessment of the consumptive use (ETC) and its components, E (S) and T, yielded seasonal values of 1088, 887, 894 and 699 mm of ETC, of which T represented 831, 640, 648 and 479 mm, for the four different treatments, respectively. The relations between yield and irrigation, ETC, and T were used to determine the WP values as affected by water. Although values varied from year to year, the WPET averaged 0.23 kg/m(3) for the 3 years and did not differ among treatments. The transpiration efficiency (WPT) had a value of 0.32 kg/m(3) and was roughly the same for all treatments.

Under localized irrigation, even when applying non-limiting amounts of water, there could be transpiration (T) limitations due to a limited wetted soil volume. To study under field conditions how drip-irrigated almond trees responded to a change in wetted soil volume, two treatments were established in summer 2012 in a drip irrigated almond orchard in Cordoba, Spain. One treatment ("Large volume") was initially irrigated with micro-sprinklers (MS) to wet the entire ground surface, and then reverted to drip irrigation, while other was always kept under drip irrigation ("Small volume"). Continuous monitoring of T and measurements of soil moisture content, tree water status and trunk growth were carried out. Even though trees in both treatments were supplied with sufficient water, the MS application induced an increase in T and an improvement in water status in "Large volume" relative to "Small volume". A reduction in the hydraulic resistance of the tree was also detected in "Large volume", as well as an enhancement in canopy conductance and tree growth. We concluded that there are situations in the field where almond tree transpiration is limited by an insufficient wetted soil volume, even when supplied with adequate water, due to a high hydraulic resistance during times of high evaporative demand.

Recently planted intensive almond plantations may have access to limited water supply due to water scarcity thus, information on almond water use under limited irrigation is needed. Here, the soil water balance was used to assess the consumptive use (ET) of full irrigated, moderately stressed and severely stressed almond trees over a three-year study, as well as the relation between applied water and ET. Sap flow measurements in eight experimental trees were used to obtain independent transpiration (T) measurements. Evaporation from soil (E-s) was modelled to estimate tree T from the water balance. Relative consumptive use in the deficit irrigation (DI) treatments largely exceeded the relative applied water, highlighting the need to measure ET in stressed treatments for hydrologic purposes. The moderately stressed treatments (irrigated at 65.5% of full irrigation) consumed 79.0% of maximum evapotranspiration (ET of 897 mm), while the severely stressed treatment consumed 63.6% of ETc (ET of 722 mm) when applied water was only 39.6% of control. On average, almond ETc approached 1200 mm, Seasonal evolution of the transpiration coefficient yielded maximum peak values ranging from 0.99 to 1.08, and minimum peak values of 0.33 attained with a severe deficit irrigation strategy. Transpiration measured by Compensated Heat Pulse -Calibrated Average Gradient sap-flow (x), was compared to water balance T estimates (y), and yielded a very good relation over the three years of study (y = 0.90x +4.23, r(2) = 0.81). The sap flow measurements proved to be useful to overcome the limitations of the soil water balance technique, revealing that almond trees were able to extract water from below the monitored depths and suggesting that deep percolation event must have occurred in spring and autumn. (C) 2017 Elsevier B.V. All rights reserved.

The responses of almond trees 'Guara' to different levels of water deficits were investigated. Three irrigation treatments as well as a rainfed treatment were applied in the field to 5-year-old trees during the summer of 2013. Plant water status was monitored by measurement of stem water potential at midday (Psi(x)), leaf gas-exchange was measured with a photosynthesis analyzer (IRGA) and stomatal conductance with a steady-state leaf porometer Psi(x) of well-watered trees was near-0.9 MPa and always higher than -1.0 MPa. In the case of trees irrigated with amounts of water below full crop requirements, Psi(x) decreased down to -1.5 MPa, and simultaneously, a gradual decrease in stomatal conductance was observed. The close correlation between stomatal conductance (gs) and CO2 assimilation (A) pointed toward the stomatal limitation of CO2 assimilation in almond. Then although the stomatal closure will reduce photosynthesis, the fact that that closure occurs gradually as stress progresses will permit some rate of CO2 assimilation by the plant. The value of -1.0 MPa could be considered a reference threshold in full irrigation programming to ensure maximum stomatal conductance of 'Guara' almond trees. That high value showed the sensibility of this cultivar to water stress.

The majority of world almond acreage is grown under rainfed conditions but most of the production is obtained under irrigation. Increased water scarcity is reducing water availability for irrigation thus the need to characterize the responses of almond to water deficits. Several works have defined well the stomatal closure in almond leaves under water deficits, but the behavior at the canopy level is not well understood. A field experiment was conducted in an almond (cv. Guara) orchard in Cordoba (Spain) under four different levels of irrigation supply to investigate the responses of almond tree transpiration (T) and transpiration efficiency (TE) to water stress. Stem water potential (Psi(x)), whole tree transpiration (T) and leaf gas-exchange were periodically measured throughout the 2013 growing season. Tree T decreased linearly as midday T decreased below a threshold value of about -1.1 MPa, and declined to about 50% of the Control value when midday Psi(x) reached -1.6 MPa. The quick decline in T in response to the lowering of mix suggests a high sensitivity of almond T to water deficits. The instantaneous transpiration efficiency (TE) of almond leaves was unaffected by water and varied essentially with vapor pressure deficits. On a daily scale, the leaf TE of stressed trees followed the same pattern as in the non-stressed trees. Then, contrary to the behavior observed in olive and citrus, there were no instantaneous or daily TE increments in almond trees in response to water deficits.

AquaCrop is a crop simulation model developed by the FAO aimed at assessing the yield response to water supply. Once the model is calibrated and validated, it is a useful tool to simulate crop yields under different management options or climatic and soil conditions. Until now, AquaCrop has not been parameterized for dry beans (Phaseolus vulgaris L.), and thus our objective was to calibrate and validate the model for this crop using experiments performed 40 years ago at Davis, California. A set of parameters derived from the calibration with one irrigation experiment was used to validate the model using five experiments carried out in 1977 and 1978 that had treatments vastly differing in irrigation depth and frequency. Yield predictions over a wide range of values (<1 to 3.5 t ha(-1)) were very good, with RMSE of 0.16 t ha(-1) and Willmott's d of 0.978. Seasonal ET was also accurately predicted by the model (RMSE = 40 mm, d = 0.930), as also evidenced by comparing the lysimeter measured ET of 489 mm against the lysimeter simulated ET of 501 mm. Canopy cover and the time course of biomass were adequately simulated as well. Even though total soil water extraction was well simulated, the simulated soil water distribution with depth differed from measured values in the dryland treatment. We conclude that AquaCrop can now be used for the simulation of dry beans in different environments, and we emphasize the value of carefully conducted field experiments for the validation of crop simulation models.

Increased water scarcity demands more efficient use of water in the agricultural sector which is the primary consumer of water. Precise determination of irrigation requirements based on specific crop parameters is needed for accurate water applications. We conducted a 4-year study on almond evapotranspiration using a large weighing lysimeter. Tree canopies changed from 3 to 48 % ground cover during the course of the study. Sap flow measurements made on the lysimeter tree provided a continuous record of tree transpiration. We propose to use the daily fraction of photosynthetically active radiation intercepted by the canopy (fIRd) as a predictor of almond orchard maximum transpiration. The transpiration coefficient (T/ET o or K T ) was related to the fIRd of the last two years, and the ratio between fIRd and K T stayed more or less constant around a value of 1.2. Such value extrapolated to the size of a mature orchard with 85 % intercepted radiation gives a K T of around 1.0, a number above the standard recommendations, but fully compatible with the maximum K c values of 1.1–1.15 recently reported.

Orchard water requirements have been the subject of controversy in recent years because the traditional methods for estimating crop ETc do not always determine correctly tree water needs. Reports of intensive almond production under full irrigation indicate that seasonal requirements exceed 1000 mm/season and that peak ETc values of 7-9 mm/day are possible. This is in contrast with traditional irrigation plantations where, given the reputation of drought resistance that almond has, seasonal amounts of 30-50% of maximum ETc are applied in some form of deficit irrigation. Experimental determination of maximum ETc using a large weighing lysimeter was started at Cordoba, Spain in 2009. Since that year, measurements of E and T together with ancillary information on tree leaf area have been taken with the aim of developing models to compute almond tree water requirements. Sap flow sensors have been installed in the experimental tree to obtain detailed T records in response to environmental conditions. The performance of different ETc models will be evaluated against actual ETc measurements.

Climate change will have important implications in the agriculture of semi-arid regions, such as Southern Spain, where the expected warmer and drier conditions might augment crop water demand. To evaluate these effects, a data set consisting of observed daily values of air temperature, relative humidity, sunshine duration and wind speed from eight weather stations in Andalusia and covering the period 1960-2005 was used for estimating reference evapotranspiration (ETo). ETo was calculated using five methods: the more complex Penman-Monteith FAO-56 (PM) equation, considered as a reference in this study, and four alternative methods with fewer data requirements, Hargreaves, Blaney-Criddle, Radiation and Priestley-Taylor. These methods were compared to PM with respect to ETo average values and trends. The non-parametric Mann-Kendall test was used to evaluate annual and seasonal trends in the main climate variables and ETo.Due to increases in air temperature and solar radiation, and decreases in relative humidity, statistically significant increases in PM-ETo were detected (up to 3.5 mm year(-1)). Although the Hargreaves equation provided the closest average values to PM, this method did not detect any ETo trend. On the other hand, trends found from Blaney-Criddle and Radiation ETo values were similar to those obtained from PM. In addition, after a local adjustment, these two methods gave accurate ETo average values. Therefore, Blaney-Criddle and Radiation methods have shown themselves to be the most accurate approaches for ETo determination in climate change studies, when available data provided by climate models are limited. (C) 2011 Elsevier B.V. All rights reserved.