Wednesday, 9 January 2019: 9:45 AM
North 127ABC (Phoenix Convention Center - West and North Buildings)
Reference evapotranspiration ETo as defined by Allen et al. (1998) in the FAO56 manual is widely used for monitoring crop water requirements and managing irrigation. ETo is computed using the Penman-Monteith (PM) equation set with fixed values of surface parameters (albedo, roughness, surface resistance) representative of a well-watered grass canopy. When considering present meteorological conditions, standard meteorological records (air temperature and humidity, wind speed, incident radiations) are used as input of the PM equation. The calculation of ETo under future climatic conditions is possible using daily atmospheric information obtained from climate simulations. However, the direct application of the PM equation does not account for the role of increasing CO2 atmospheric concentration ([CO2]a) which has a strong impact on stomatal processes (e.g. Bunce 2004). Olioso et al. (2010) proposed to simulate the impact of CO2 on ETo using a soil-vegetation-atmosphere transfer model and to establish a formula to "correct" standard ETo calculations (EToFAO56) to account for the anti-transpiring effect of CO2. This formula can be applied to analyze future evolutions of ETo.
In this work we used the ISBA-A-gs model (Calvet et al., 1998) that simulated soil-vegetation-atmosphere transfers based on meteorological data, vegetation type and soil type. It explicitly described the effects of [CO2]a on stomatal processes through a coupled parameterization of stomatal conductance and leaf photosynthesis (Jacobs 1994). ISBA-A-gs simulations for the reference grass under conditions with [CO2]a = 370 ppm were in good agreement with standard ETo calculations following FAO56 procedures. When [CO2]a increased, ETo decreased by up to 20% when [CO2]a reached 900 ppm. At 550 ppm, ETo decreased by 8%. The decrease of ETo was almost linear with the increase in [CO2]a. When considering daily value in detail, the decrease in ETo also depended on the level of evapotranspiration, with the highest ETo being the most affected. ISBA-A-gs simulations at different levels of [CO2]a were used for establishing formulas which made it possible to compute reference ET at any CO2 concentration (ETo[CO2]a) from standard reference evapotranspiration (EToFAO56). A simple linear formula, dependent on [CO2]a (in ppm) was proposed when considering yearly time scale:
ETo [CO2]a = (1.1403 – 3.8979.10-4 * [CO2]a) * EToFAO56.
Compared with ISBA-A-gs simulations, the root mean squared difference was 0.13 mm d-1. It was also possible to develop a more complex formula taking into account the different nonlinearities and improving the calculation of ETo at the daily scale (but not at the annual scale).
In a second step, we applied the previous formula to different climate change scenarios in order to derive the reference ET with changing CO2 (and climate) conditions. Calculations of EToFAO56 were performed for the SRES B1 scenarios ([CO2]a = 540 ppm in 2100), A1B (703 ppm) and A2 (836 ppm) using the Quantile-Quantile (QQ) dynamic regionalization method over several locations in France (see Boe et al. 2007, Terray et al., 2010). The results, presented for two contrasted climates, Avignon in South of France and Mons in North of France (see Figure), showed a sharp increase in EToFAO56 starting in 2020. Increases reached 50 to 100 mm y-1 for the 'near future' period (2020-2049) and 125 to 250 mm y-1 for the 'distant future' period (2070-2099) depending on the climate scenario. The most pessimistic scenarios generally led to the largest increases. ETo increases resulted from both increases in insolation and in air saturation deficit. Taking CO2 into account strongly modified the evolutions of ETo (see Figure), the increases being not larger than 50 mm y-1 in the near future period and between 30 to 120 mm y-1 in the distant future period. In contrast to the standard FAO56 calculations, the most pessimistic scenarios led to the smallest increases as the highest CO2 concentrations resulted in the largest corrections.
Our study shows that not accounting for CO2 effect on stomatal regulation may lead to erroneous prediction of crop water requirements in the future. However, our results only concerned the definition of the reference evapotranspiration that has to be accounted in crop water requirement calculations. Other factors, as in particular the temperature which is strongly affecting plant phenology and the adaptation of agricultural practices, are also to be accounted when estimating future crop water requirements. Future works should also analyze the impact of differing stomatal response to CO2 depending on plant species or cultivar.
References:
Allen R.G., L.S. Pereira, D. Raes, M. Smith, 1998. Crop evapotranspiration: guidelines for computing crop water requirements. Irrigation and Drainage Paper 56, United Nations Food and Agriculture Organization, Rome, Italy. 300 p.
Boe J., Terray L., Habets F., Martin E., 2007. Statistical and dynamical downscaling of the Seine basin climate for hydro-meteorological studies. International Journal of Climatology, 27, 1643-1655.
Bunce JA, 2004. Carbon dioxide effects on stomatal responses to the environment and water use by crops under field conditions. Oecologia 140 (1): 1-10.
Calvet, J.-C., Noilhan, J., Roujean, J.-L., Bessemoulin, P., Cabelguenne, M., Olioso, A., et Wigneron, J.-P., 1998. An interactive vegetation SVAT model tested against data from six contrasting sites. Agricultural and Forest Meteorology, 92, 73-95.
Jacobs C.M.J., 1994. Direct impact of atmospheric CO2 enrichment on regional transpiration. PhD-thesis, Wageningen University, 179 p.
Olioso A., Huard F., Guilioni L., 2010. Prise en compte des effets du CO2 sur le calcul de l'évapotranspiration de référence. Colloque final du projet CLIMATOR, 17-18 juin, Versailles. Organisé par INRA et ARVALIS
Terray L., Pagé C., Déqué M., Flécher C., 2010. L’évolution du climat en France basée sur les projections climatiques utilisées dans CLIMATOR au travers de quelques indicateurs agroclimatiques. Livre Vert du Projet Climator, published by ADEME.
In this work we used the ISBA-A-gs model (Calvet et al., 1998) that simulated soil-vegetation-atmosphere transfers based on meteorological data, vegetation type and soil type. It explicitly described the effects of [CO2]a on stomatal processes through a coupled parameterization of stomatal conductance and leaf photosynthesis (Jacobs 1994). ISBA-A-gs simulations for the reference grass under conditions with [CO2]a = 370 ppm were in good agreement with standard ETo calculations following FAO56 procedures. When [CO2]a increased, ETo decreased by up to 20% when [CO2]a reached 900 ppm. At 550 ppm, ETo decreased by 8%. The decrease of ETo was almost linear with the increase in [CO2]a. When considering daily value in detail, the decrease in ETo also depended on the level of evapotranspiration, with the highest ETo being the most affected. ISBA-A-gs simulations at different levels of [CO2]a were used for establishing formulas which made it possible to compute reference ET at any CO2 concentration (ETo[CO2]a) from standard reference evapotranspiration (EToFAO56). A simple linear formula, dependent on [CO2]a (in ppm) was proposed when considering yearly time scale:
ETo [CO2]a = (1.1403 – 3.8979.10-4 * [CO2]a) * EToFAO56.
Compared with ISBA-A-gs simulations, the root mean squared difference was 0.13 mm d-1. It was also possible to develop a more complex formula taking into account the different nonlinearities and improving the calculation of ETo at the daily scale (but not at the annual scale).
In a second step, we applied the previous formula to different climate change scenarios in order to derive the reference ET with changing CO2 (and climate) conditions. Calculations of EToFAO56 were performed for the SRES B1 scenarios ([CO2]a = 540 ppm in 2100), A1B (703 ppm) and A2 (836 ppm) using the Quantile-Quantile (QQ) dynamic regionalization method over several locations in France (see Boe et al. 2007, Terray et al., 2010). The results, presented for two contrasted climates, Avignon in South of France and Mons in North of France (see Figure), showed a sharp increase in EToFAO56 starting in 2020. Increases reached 50 to 100 mm y-1 for the 'near future' period (2020-2049) and 125 to 250 mm y-1 for the 'distant future' period (2070-2099) depending on the climate scenario. The most pessimistic scenarios generally led to the largest increases. ETo increases resulted from both increases in insolation and in air saturation deficit. Taking CO2 into account strongly modified the evolutions of ETo (see Figure), the increases being not larger than 50 mm y-1 in the near future period and between 30 to 120 mm y-1 in the distant future period. In contrast to the standard FAO56 calculations, the most pessimistic scenarios led to the smallest increases as the highest CO2 concentrations resulted in the largest corrections.
Our study shows that not accounting for CO2 effect on stomatal regulation may lead to erroneous prediction of crop water requirements in the future. However, our results only concerned the definition of the reference evapotranspiration that has to be accounted in crop water requirement calculations. Other factors, as in particular the temperature which is strongly affecting plant phenology and the adaptation of agricultural practices, are also to be accounted when estimating future crop water requirements. Future works should also analyze the impact of differing stomatal response to CO2 depending on plant species or cultivar.
References:
Allen R.G., L.S. Pereira, D. Raes, M. Smith, 1998. Crop evapotranspiration: guidelines for computing crop water requirements. Irrigation and Drainage Paper 56, United Nations Food and Agriculture Organization, Rome, Italy. 300 p.
Boe J., Terray L., Habets F., Martin E., 2007. Statistical and dynamical downscaling of the Seine basin climate for hydro-meteorological studies. International Journal of Climatology, 27, 1643-1655.
Bunce JA, 2004. Carbon dioxide effects on stomatal responses to the environment and water use by crops under field conditions. Oecologia 140 (1): 1-10.
Calvet, J.-C., Noilhan, J., Roujean, J.-L., Bessemoulin, P., Cabelguenne, M., Olioso, A., et Wigneron, J.-P., 1998. An interactive vegetation SVAT model tested against data from six contrasting sites. Agricultural and Forest Meteorology, 92, 73-95.
Jacobs C.M.J., 1994. Direct impact of atmospheric CO2 enrichment on regional transpiration. PhD-thesis, Wageningen University, 179 p.
Olioso A., Huard F., Guilioni L., 2010. Prise en compte des effets du CO2 sur le calcul de l'évapotranspiration de référence. Colloque final du projet CLIMATOR, 17-18 juin, Versailles. Organisé par INRA et ARVALIS
Terray L., Pagé C., Déqué M., Flécher C., 2010. L’évolution du climat en France basée sur les projections climatiques utilisées dans CLIMATOR au travers de quelques indicateurs agroclimatiques. Livre Vert du Projet Climator, published by ADEME.
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