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The AquaCrop simulation model, originally designed for annual crops, is expanded here to simulate alfalfa, a perennial forage crop. A new routine was added to the model to mimic the assimilate partitioning between above and below-ground plant parts to account for the utilization of reserves in Spring and for their storage in the Fall. The simulation of the transfer of assimilates requires only three extra crop parameters which makes the model also easy to calibrate. To evaluate the model, yield data collected in Louvain-La-Neuve (Belgium), Isparta (Turkey), and Ottawa (Canada) for different alfalfa cultivars, various years and field and irrigation management strategies were used. To assess the accuracy and robustness of the simple assimilate remobilization process, simulations were run for the three different environments with a common set of crop parameters which were parameterized. The dispersion between the observed and simulated cumulative dry above-ground biomass during the growing cycle was small (r² = 0.97; nRMSE = 11%; Nash-Sutcliffe model EF = 0.97), and a systematic over- or underestimation by the model was not observed (Willmott's index of agreement, d = 0.99). When evaluating the goodness of fit of the 81 individual harvest events, the results were still very satisfactory although the nRMSE doubled. The simulations indicated that the AquaCrop model adapted to perennial crops and with a novel storage-remobilization routine, could predict well alfalfa yields in various climates and environments, with and without water and fertility stress, and for three different alfalfa cultivars.

FAO's water-driven crop growth simulation model, AquaCrop, was calibrated and validated for cassava (Manihot esculenta Crantz). Existing datasets, used in similar published works, were shared covering several years and regions (Colombia, Nigeria and Togo). Different varieties were tested for the case of Colombia and a single variety (TME-419) for Nigeria and Togo. Overall calibrated biomass simulations resulted in an R2 of 0.96 and a RMSE of 1.99 tonne DM/ha. As for dry tuber yield estimates, it was not possible to find a single harvest index for the ensembled varieties given their varying characteristics and limited data per variety. However, for the TME-419 variety (Nigeria and Togo) calibrated root tuber simulations yielded and R2 of 0.94 and a RMSE of 2.37 tonne DM/ha. A single crop-file was developed for different cassava varieties and agro-ecological regions, which can be applied with confidence to further study cassava related food security, water productivity, improved agronomic practices, etc.

Global soil water availability is challenged by the effects of climate change and a growing population. On average, 70 % of freshwater extraction is attributed to agriculture, and the demand is increasing. In this study, the effects of climate change on the evolution of the irrigation water requirement to sustain current crop productivity are assessed by using the Food and Agriculture Organization (FAO) crop growth model AquaCrop version 6.1. The model is run at resolution over the European mainland, assuming a general C3-type of crop, and forced by climate input data from the Inter-Sectoral Impact Model Intercomparison Project phase three (ISIMIP3). First, the AquaCrop surface soil moisture (SSM) forced with two types of ISIMIP3 historical meteorological datasets is evaluated with satellite-based SSM estimates in two ways. When driven by ISIMIP3a reanalysis meteorology, daily simulated SSM values have an unbiased root mean square difference of 0.08 and 0.06 m3 m−3, with SSM retrievals from the Soil Moisture Ocean Salinity (SMOS) and Soil Moisture Active Passive (SMAP) missions, respectively, for the years 2015–2016 (2016 is the end year of the reanalysis data). When forced with ISIMIP3b meteorology from five global climate models (GCMs) for the years 2015–2020, the historical simulated SSM climatology closely agrees with the satellite-based SSM climatologies. Second, the evaluated AquaCrop model is run to quantify the future irrigation requirement, for an ensemble of five GCMs and three different emission scenarios. The simulated net irrigation requirement (Inet) of the three summer months for a near and far future climate period (2031–2060 and 2071–2100) is compared to the baseline period of 1985–2014 to assess changes in the mean and interannual variability of the irrigation demand. Averaged over the continent and the model ensemble, the far future Inet is expected to increase by 22 mm per month (+30 %) under a high-emission scenario Shared Socioeconomic Pathway

The current intensive use of agricultural land is affecting the land quality and contributes to climate change. Feeding the world's growing population under changing climatic conditions demands a global transition to more sustainable agricultural systems. This requires efficient models and data to monitor land cultivation practices at the field to global scale. This study outlines a spatially distributed version of the field-scale crop model AquaCrop version 6.1 to simulate agricultural biomass production and soil moisture variability over Europe at a relatively fine resolution of 30 arcsec (∼1 km). A highly efficient parallel processing system is implemented to run the model regionally with global meteorological input data from the Modern-Era Retrospective analysis for Research and Applications version 2 (MERRA-2), soil textural information from the Harmonized World Soil Database version 1.2 (HWSDv1.2), and generic crop information. The setup with a generic crop is chosen as a baseline for a future satellite-based data assimilation system. The relative temporal variability in daily crop biomass production is evaluated with the Copernicus Global Land Service dry matter productivity (CGLS-DMP) data. Surface soil moisture is compared against NASA Soil Moisture Active–Passive surface soil moisture (SMAP-SSM) retrievals, the Copernicus Global Land Service surface soil moisture (CGLS-SSM) product derived from Sentinel-1, and in situ data from the International Soil Moisture Network (ISMN). Over central Europe, the regional AquaCrop model is able to capture the temporal variability in both biomass production and soil moisture, with a spatial mean temporal correlation of 0.8 (CGLS-DMP), 0.74 (SMAP-SSM), and 0.52 (CGLS-SSM). The higher performance when evaluating with SMAP-SSM compared to Sentinel-1 CGLS-SSM is largely due to the lower quality of CGLS-SSM satellite retrievals under growing vegetation. The regional model further captures the short-term and inter-annual varia

Water resources are linked to the global challenges of food insecurity and poverty, as well as to climate change adaptation and mitigation. In line with the Sustainable Development Goals (SGD), FAO works towards several dimensions of sustainable development, including the promotion of coherent approaches to efficient, productive and sustainable water management, from farm to river basin scales. Accordingly, FAO is enhancing well-informed on-the-ground decision-making processes on water management through projects, knowledge advancement, information-sharing and tools development, such as AquaCrop, the FAO crop-water productivity model. This model assists in assessing the effects of environment (including atmospheric CO2 concentration) and management on crop production through the simulation of yield response to water of herbaceous crops. It is particularly suited to address conditions where water is a key limiting factor in crop production. In 2009, FAO officially launched AquaCrop, being the result of several years of collaborative work among scientists, water and crop specialists and practitioners worldwide, bringing together previously fragmented information on crop yields in response to water use and water deficit. AquaCrop has evolved over the different versions released since its first launch, but it always balances accuracy, simplicity and robustness. This has enabled it to remain faithful to its goal, i.e., to be a dynamic tool accessible to several types of users, mainly practitioner-type end users, in different disciplines and for a wide range of applications. In addition, AquaCrop may be considered a valuable tool by research scientists for analysis and conceptualization.

Crop simulation models are valuable tools for quantifying crop yield response to water, and for devising strategies to improve agricultural water management. However, applicability of the majority of crop models is limited greatly by a failure to provide open-access to model source code. In this study, we present an open-source version of the FAO AquaCrop model, which simulates efficiently water-limited crop production across diverse environmental and agronomic conditions. Our model, called AquaCrop-OpenSource (AquaCrop-OS), can be run in multiple programming languages and operating systems. Support for parallel execution reduces significantly simulation times when applying the model in large geospatial frameworks, for long-run policy analysis, or for uncertainty assessment. Furthermore, AquaCrop-OS is compliant with the Open Modelling Interface standard facilitating linkage to other disciplinary models, for example to guide integrated water resources planning.

La technologie d’irrigation goutte-à-goutte est fréquemment promue en raison du potentiel d’économie d’eau d’irrigation qu’elle représente. Ce travail fait le point sur l’impact potentiel de cette technologie sur les ressources en eau mais envisage également une perspective plus large qui intègre la multiplicité des préoccupations des acteurs de l’agriculture. L’objectif global de ce travail est de démontrer que les objectifs de la conversion à l’irrigation goutte-à-goutte diffèrent entre les gestionnaires des réseaux d’irrigation et ses principaux utilisateurs. Une méthodologie en deux temps est implémentée pour étudier cette question dans la plaine des Triffa (Maroc Oriental). La première partie du travail se focalise sur la notion d’efficience de l’irrigation tandis que la seconde élève la réflexion au niveau des performances globales de l’irrigation. La notion d’effet d’usage est d’abord quantifiée. Le comportement de l’agriculteur aurait ainsi un impact prépondérant sur les valeurs d’efficience. La relation entre technique d’irrigation et gestion est ensuite explicitée. L’estimation de l’effet d’usage est ainsi rendue possible. L’impact de la transition à l’irrigation goutte-à-goutte sur les ressources en eau peut alors être étudié. La demande en eau augmente suite à cette transition. Les pressions sur la nappe d’eau souterraine seraient par contre atténuées en raison d’un transfert accru depuis le barrage vers la nappe. L’impact de la transition à l’irrigation goutte-à-goutte n’entraine donc pas de diminution systématique des pressions sur les ressources en eau. L’impact de la transition en termes de performance du système d’irrigation du point de vue des agriculteurs est ensuite étudié. Cette analyse exclut les questions de qualité. Aucune amélioration de performance n’est observée sur le plan environnemental. L’impact économique de cette transition est faible. Sur le plan social, le principal avantage de l’irrigation goutte-à-goutte réside dans le mode d’org, (AGRO - Sciences agronomiques et ingénierie biologique) -- UCL, 2016

AquaCrop, the FAO water productivity model, is used as a tool to predict crop production under water limiting conditions. In the first step AquaCrop was calibrated and validated for barley (Hordeum vulgare L.). Data sets of field experiments at seven different locations in four countries (Ethiopia, Italy, Syria and Montana, USA) with different climates in different years and with five different cultivars were used for model calibration and validation. The goodness-of-fit between observed and simulated soil water content, green canopy cover, biomass and grain yield was assessed by means of the coefficient of determination (R 2), the Nasha-Sutcliff efficiency (E), the index of agreement (d) and the root mean square error (RMSE). The statistical parameters indicated an adequate accuracy of simulations (validation regression of yield: R 2 = 0.95, E = 0.94, d = 0.99, RMSE = 0.34). Subsequently, sowing strategies in the semi-arid environment of northern Ethiopia were evaluated with the validated model. Dry sowing had a probability of 47% germination failure attributable to false start of the rainy season. On the other hand, delay sowing at the start of the rainy season to eliminate germinating weeds should be kept as short as possible because grain yields strongly reduce in the season due to water stress when sowing is delayed on shallow soils. This research demonstrates the ability of AquaCrop to predict accurately crop performance with only a limited set of input variables, and the robustness of the model under various environmental and climatic conditions. © 2012 Cambridge University Press.

AquaCrop, the FAO water productivity model, is used as a tool to predict crop production under water limiting conditions. In the first step AquaCrop was calibrated and validated for barley (Hordeum vulgare L.). Data sets of field experiments at seven different locations in four countries (Ethiopia, Italy, Syria and Montana, USA) with different climates in different years and with five different cultivars were used for model calibration and validation. The goodness-of-fit between observed and simulated soil water content, green canopy cover, biomass and grain yield was assessed by means of the coefficient of determination (R 2), the Nasha-Sutcliff efficiency (E), the index of agreement (d) and the root mean square error (RMSE). The statistical parameters indicated an adequate accuracy of simulations (validation regression of yield: R 2 = 0.95, E = 0.94, d = 0.99, RMSE = 0.34). Subsequently, sowing strategies in the semi-arid environment of northern Ethiopia were evaluated with the validated model. Dry sowing had a probability of 47% germination failure attributable to false start of the rainy season. On the other hand, delay sowing at the start of the rainy season to eliminate germinating weeds should be kept as short as possible because grain yields strongly reduce in the season due to water stress when sowing is delayed on shallow soils. This research demonstrates the ability of AquaCrop to predict accurately crop performance with only a limited set of input variables, and the robustness of the model under various environmental and climatic conditions. © 2012 Cambridge University Press.

The AquaCrop model was developed to replace the former FAO I&D Paper 33 procedures for the estimation of crop productivity in relation to water supply and agronomic management in a framework based on current plant physiological and soil water budgeting concepts. This paper presents the software of AquaCrop for which the concepts and underlying principles are described in the companion paper (Steduto et al., 2009). Input consists of weather data, crop characteristics, and soil and management characteristics that define the environment in which the crop will develop. Algorithms and calculation procedures modeling the infiltration of water, the drainage out of the root zone, the canopy and root zone development, the evaporation and transpiration rate, the biomass production, and the yield formation are presented. The mechanisms of crop response to cope with water shortage are described by only a few parameters, making the underlying processes more transparent to the user. AquaCrop is a menu-driven program with a well-developed user interface. With the help of graphs which are updated each time step (1 d) during the simulation run, the user can track changes in soil water content, and the corresponding changes in crop development, soil evaporation and transpiration rate, biomass production, and yield development. One can halt the simulation at each time step, to study the effect of changes in water related inputs, making the model particularly suitable for developing deficit irrigation strategies and scenario analysis.

The first crop chosen to parameterize and test the new FAO AquaCrop model is maize (Zea mays L.). Working mainly with data sets from 6 yr of maize fi eld experiments at Davis, CA, plus another 4 yr of Davis maize canopy data, a set of conservative (nearly constant) parameters of AquaCrop, presumably applicable to widely different conditions and not specifi c to a given crop cultivar, was evaluated by test simulations, and used to simulate the 6 yr of Davis data. The treatment variable was irrigation-withholding water aft er planting continuously, only up to tasseling, from tasseling onward, or intermittently, and with full irrigation (FI) as the control. From year to year, plant density (7-11.9 plants m-2), planting date (14 May-15 June), cultivar (a total of four), and atmospheric evaporative demand varied. The conservative parameters included: canopy growth and canopy decline coeffi cient (CDC); crop coeffi cient for transpiration (Tr) at full canopy; normalized water productivity for biomass (WP*); soil water depletion thresholds for the inhibition leaf growth and of stomatal conductance, and for the acceleration of canopy senescence; reference harvest index (HIo); and coeffi cients for adjusting harvest index (HI) in relation to inhibition of leaf growth and of stomatal conductance. With all 19 parameters held constant, AquaCrop simulated the fi nal aboveground biomass within 10% of the measured value for at least 8 of the 13 treatments (6 yr of experiments) and also the grain yield for at least fi ve of the cases. In at least four of the cases, the simulated results were within 5% of the measured for biomass as well as for grain yield. The largest deviation between the simulated and measured values was 22% for biomass, and 24% for grain yield. Importantly, the simulated pattern of canopy progression and biomass accumulation over time were close to those measured, with Willmott's index of agreement (d) for 11 of the 13 cases being =0.98 for canopy cover (CC), an

This article introduces the FAO crop model AquaCrop. It simulates attainable yields of major herbaceous crops as a function of water consumption under rainfed, supplemental, deficit, and full irrigation conditions. The growth engine of AquaCrop is water-driven, in that transpiration is calculated fi rst and translated into biomass using a conservative, crop-specifi c parameter: the biomass water productivity, normalized for atmospheric evaporative demand and air CO2 concentration. The normalization is to make AquaCrop applicable to diverse locations and seasons. Simulations are performed on thermal time, but can be on calendar time, in daily time-steps. The model uses canopy ground cover instead of leaf area index (LAI) as the basis to calculate transpiration and to separate out soil evaporation from transpiration. Crop yield is calculated as the product of biomass and harvest index (HI). At the start of yield formation period, HI increases linearly with time aft er a lag phase, until near physiological maturity. Other than for the yield, there is no biomass partitioning into the various organs. Crop responses to water deficits are simulated with four modifi ers that are functions of fractional available soil water modulated by evaporative demand, based on the differential sensitivity to water stress of four key plant processes: canopy expansion, stomatal control of transpiration, canopy senescence, and HI. The HI can be modifi ed negatively or positively, depending on stress level, timing, and canopy duration. AquaCrop uses a relatively small number of parameters (explicit and mostly intuitive) and attempts to balance simplicity, accuracy, and robustness. The model is aimed mainly at practitioner-type end-users such as those working for extension services, consulting engineers, governmental agencies, nongovernmental organizations, and various kinds of farmers associations. It is also designed to fi t the need of economists and policy specialists who use simple mode

[i] Water Users Associations (WUAs) are all too often considered a panacea for improving water management in irrigation schemes. Where grassroots movements are absent, they are usually imposed on farmers by national governments, NGOs, and international donors, without fully considering existing forms of organization. This also happened in the Office du Niger irrigation scheme in Mali, where after a partial irrigation management transfer, WUAs were created to fill the resulting power vacuum. This paper demonstrates that, despite active efforts to organize farmers in WUAs, informal patterns of decision making remain dominant. Given the shortcomings of these informal patterns, WUAs could provide a much-needed platform for institutionalizing collective action, on the condition that farmers accept them. Therefore WUAs should adopt some crucial characteristics of informal patterns of decision making while avoiding their weaknesses. First, making use of the existing authority of village leadership and the central management can improve the credibility of WUAs. Second, allowing flexibility in procedures and rules can make them more appropriate for dealing with collective action problems that are typically temporary and specific. Last, formalizing the current pattern of conflict management and sanctioning might enhance its sphere of action and tackle the current absence of firm engagement with respect to some informal management decisions. In addition, WUAs should represent and be accountable to all farmers, including those residing outside the village community.

This paper investigates the relation between collective action and performance for a case study in the Office du Niger irrigation scheme in Mali. As a result of irrigation management transfer at tertiary level, farmers are now collectively responsible for water supply to the tertiary block, water allocation within the tertiary block, coordination of the cropping calendar and infrastructure maintenance. The research is based on a field study including about 300 farmers from 36 tertiary blocks and 9 villages. First, the different aspects of both collective action and performance are measured through developing indicators. Regarding collective action, these indicators measure coordination of the cropping calendar, maintenance of tertiary infrastructure, coordination of water demand at tertiary level, and coordination of water allocation within the tertiary block. The performance indicators incorporate the viewpoint of the irrigation scheme's management as well as farmers and are irrigation efficiency, easiness of irrigation, occurrence of conflicts and agricultural productivity. Next, the relation between collective action and irrigation performance is quantified using statistical models. The main finding is that not all aspects of performance are affected by collective action, and when they do, not by all aspects of collective action. The choice of indicators when studying collective action is thus of primary importance. In the Office du Niger, coordination of water supply and demand and coordination of water allocation affect efficiency and easiness of irrigation respectively. Given the increasing importance of these aspects of performance, they must form the primary focus of efforts to enhance collective action.

This paper investigates the relation between collective action and performance for a case study in the Office du Niger irrigation scheme in Mali. As a result of irrigation management transfer at tertiary level, farmers are now collectively responsible for water supply to the tertiary block, water allocation within the tertiary block, coordination of the cropping calendar and infrastructure maintenance. The research is based on a field study including about 300 farmers from 36 tertiary blocks and 9 villages. First, the different aspects of both collective action and performance are measured through developing indicators. Regarding collective action, these indicators measure coordination of the cropping calendar, maintenance of tertiary infrastructure, coordination of water demand at tertiary level, and coordination of water allocation within the tertiary block. The performance indicators incorporate the viewpoint of the irrigation scheme's management as well as farmers and are irrigation efficiency, easiness of irrigation, occurrence of conflicts and agricultural productivity. Next, the relation between collective action and irrigation performance is quantified using statistical models. The main finding is that not all aspects of performance are affected by collective action, and when they do, not by all aspects of collective action. The choice of indicators when studying collective action is thus of primary importance. In the Office du Niger, coordination of water supply and demand and coordination of water allocation affect efficiency and easiness of irrigation respectively. Given the increasing importance of these aspects of performance, they must form the primary focus of efforts to enhance collective action.

La confrontation de l'offre en eau des gestionnaires de périmètre irrigué avec les demandes des agriculteurs est source fréquente de conflits. Ceux-ci renvoient au fossé existant entre les normes de conception des aménagements et leur évolution ultérieure, que ce soit en termes structurels (surfaces irriguées, systèmes d'irrigation) ou fonctionnels (assolement, règles de gestion). Cette étude, basée sur une intervention conduite sur deux périmètres irrigués brésiliens, vise à concevoir un outil de simulation permettant d'aider gestionnaires et agriculteurs à négocier autour de nouvelles formes d'organisation de la distribution en eau. Nous montrons dans un premier temps comment l'évolution des cas étudiés a conduit à des tensions sur l'offre. Puis nous présentons la structure générale du modèle adoptée et les principes de calcul de la demande en eau des agriculteurs et de l'offre du gestionnaire. Un exemple simple de simulation vient illustrer la démarche employée. Nous montrons comment elle permet de passer d'indicateurs tels que la couverture des demandes par l'offre, à des considérations plus organisationnelles. Les perspectives offertes par ce travail en terme de conseil sont exposées en conclusion.

La confrontation de l'offre en eau des gestionnaires de périmètre irrigué avec les demandes des agriculteurs est source fréquente de conflits. Ceux-ci renvoient au fossé existant entre les normes de conception des aménagements et leur évolution ultérieure, que ce soit en termes structurels (surfaces irriguées, systèmes d'irrigation) ou fonctionnels (assolement, règles de gestion). Cette étude, basée sur une intervention conduite sur deux périmètres irrigués brésiliens, vise à concevoir un outil de simulation permettant d'aider gestionnaires et agriculteurs à négocier autour de nouvelles formes d'organisation de la distribution en eau. Nous montrons dans un premier temps comment l'évolution des cas étudiés a conduit à des tensions sur l'offre. Puis nous présentons la structure générale du modèle adoptée et les principes de calcul de la demande en eau des agriculteurs et de l'offre du gestionnaire. Un exemple simple de simulation vient illustrer la démarche employée. Nous montrons comment elle permet de passer d'indicateurs tels que la couverture des demandes par l'offre, à des considérations plus organisationnelles. Les perspectives offertes par ce travail en terme de conseil sont exposées en conclusion.

In order to adjust correctly the irrigation calendar to actual weather and water limiting conditions, farmers require guidelines to help them in their day to day decisions. In this paper a procedure is outlined to present such guidelines in the form of a single chart. On the chart information concerning the irrigation interval and irrigation duration is presented. Tables guide the user (i) to adjust the irrigation interval to the actual weather conditions throughout the growing season and (ii) to select the duration of the water application as a function of the characteristics of the irrigation system. In case of water shortage during a particular period, additional data informs the user on the sensitivity of the crop to water stress. An example is presented for drip irrigated tomatoes in the region of Tunis on a fluvisol.

This online report from the Food and Agriculture Organization of the United Nations is a rich resource on evapotranspiration. The document includes a comprehensive introduction to evapotranspiration, methods of calculation, and an examination of evapotranspiration in crops. The report is easy to navigate with a detailed table of contents; navigational buttons; and links to figures, tables, and subsections.

This online report from the Food and Agriculture Organization of the United Nations is a rich resource on evapotranspiration. The document includes a comprehensive introduction to evapotranspiration, methods of calculation, and an examination of evapotranspiration in crops. The report is easy to navigate with a detailed table of contents; navigational buttons; and links to figures, tables, and subsections.

This publication presents an updated procedure for calculating reference and crop evapotranspiration from meteorological data and crop coefficients. The procedure, first presented in the FAO Irrigation and Drainage Paper No. 24 'Crop Water Requirements', is termed the 'Kc ETo' approach, whereby the effect of the climate on crop water requirements is given by the reference evapotranspiration ETo and the effect of the crop by the crop coefficient Kc. Other procedures developed in FAO Irrigation and Drainage Paper No. 24 such as the estimation of dependable and effective rainfall, the calculation of irrigation requirements and the design of irrigation schedules are not presented in this publication but will be the subject of later papers in the series.