the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 15 Nov 2024
Ozone pollution may limit the benefits of irrigation to wheat productivity in India
Abstract. Ground level ozone (O3) pollution, heat and water stress are recognised as key abiotic stresses which threaten the ability of wheat yields to meet the growing demand for food production in India. The magnitude and interplay of O3 and water-stress effects are tightly coupled via stomatal conductance and the transpiration pathway. Existing modelling methods that assess stress response as a function of O3- and water vapour-stomatal flux are applied to assess O3’s role in limiting productivity afforded by irrigation. We investigate the effect of these stresses on grain yield of older (HUW-234) vs recently released (HD-3118) Indian wheat cultivars under current and future climates and O3 precursor emission profiles (using RCP4.5 and RCP8.5 scenarios). Water-stress in rainfed conditions was modelled to analyse the trade-off between O3-induced vs. water-stress-induced yield loss to quantify the extent to which water-stress mitigates O3 stress via reduced stomatal conductance. Under rainfed conditions for the years 1996-2005, the mean water-stress-induced and O3-induced yield loss for HUW-234 was 13.3 % and 0.6 % respectively. The latter was a significant decrease from the mean O3-induced yield loss of 10.6 % modelled under irrigated conditions (i.e. no water stress). Similarly, under RCP4.5 and RCP8.5 scenarios for the mid-century, water-stress induced yield losses under rainfed conditions were 10.1 % and 20.0 %, while mean O3-induced yield losses were only 1.0 % and 0.1 % respectively. Under irrigation, O3-induced yield losses increased to 18.5 % and 13.7 %, suggesting that O3 stress will negate the beneficial effects of irrigation. The cultivar HD-3118 suffered on average 0.2 % greater O3 relative yield loss (O3RYL) than HUW-234 across all scenarios. The O3RYL increased with climate change under the RCP4.5 scenario by 7.9 % and RCP8.5 by 3.0 % compared to the current climate. Together these findings suggest that O3 may continue to substantially limit the productivity benefits of the use of modern cultivars bred for high gas exchange grown under irrigated conditions in India.
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Status: open (until 24 Jan 2025)
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RC1: 'Comment on egusphere-2024-3371', Anonymous Referee #1, 19 Dec 2024
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General comment:
This paper presents ozone and water-stress impact on wheat productivity under current and future climate scenarios in India to highlight the importance of the irrigation for crop production. The effects of ozone stress on the yield under the different humidity and climate conditions were quantified based on WRF model simulation, and their sensitivities influenced by climate and plant were discussed. Overall, the study addresses a significant gap in the understanding of the agricultural impact of ozone and its coupling with water stress in India, a region experiencing increasing ozone pollution. The conception is interesting and impressive. However, authors only discuss the average result of ozone impact during the study period, the spatial and temporal variations of ozone impact are not included, which need more comprehensive investigations. Additionally, the method introduction should be more specific and detailed.
The following changes should be made to improve the manuscript with respect to clarity, information content and thus value to the reader.
Specific questions/issues:
Table 1： Temperature（°c）→℃
Line 192: How to calculate the RstoH2O? based on Gsto?
Line 199-200: “K𝑦 is the crop-specific yield response factor assumed to be 1.15 for the whole growing season” Are there any difference for the response factor of different wheat cultivars? as the different stomatal sensitivity and gmax.
Table 2: Canopy height: How about the variability of canopy height? Canopy height depends on wheat growth, and it increases from 0 m after sowing to the maximum height (~ 1 m) at the end of growth stage. Why do you choose the maximum height as canopy height in the simulation? How does the height affect the simulation? (Crop height: https://doi.org/10.1007/s12524-024-02028-4)
Section 2: The method of chemistry simulation and evaluation in WRF model should be added, as ozone concentration is critical to ozone uptake and impact.
Section 3.1: Although phenology is crucial for leaf stomatal conductance and ozone uptake, the magnitude of ozone uptake is the most important for the accurate evaluation of ozone impact on yield loss. How do you assess the uncertainty of modelled POD?
Section 3.2: What is the definition of water-stress condition? Are there any indexes or indicators to measure the humidity? As POD is a cumulative metric for the whole period of wheat growth, how do you simulate the cumulative ozone flux under two humidity conditions? How about the spatial distribution of O3-related yield loss and WSRYL?
Line 289-292: “Under rainfed conditions, mean O3RYL was projected to be negligible (0.6%), significantly lower than the mean O3RYL when no water-stress is assumed under irrigation (10.7% with a range of 4.8-15.4%). This demonstrates the importance of irrigation for wheat production in India and highlights the substantial influence on the yield of O3 for irrigated wheat.” What are the main pathways through which the irrigation could reduce ozone impact? and their relative contributions?
Lines 328-330: “The current climate represents the lowest mean O3, suggesting O3, rather than other environmental conditions that might influence sensitivity to O3, is the most important factor in determining O3-induced yield loss.” Please rephrase this sentence, it’s a bit hard to understand. Whose sensitivity do the environmental conditions influence?
Lines 350-355: “Whilst the RCP4.5 scenario sees a global reduction in [O3] due to pollution regulation, the South Asian region is an exception to this rule, where [O3] continues to increase at a similar rate as occurred in previous decades (Tai and Martin, 2017). RCP8.5 projects a worldwide increase in [O3] due to the lack of regulation of precursor emissions except in parts of the US, East and Southeast Asia (Tai and Martin, 2017). Therefore, mean [O3] during the growing season is lowest in the current climate at 48.6ppb but similar, at least in South Asia, in both the RCP4.5 and RCP8.5 scenarios (60.5ppb and 59.7ppb respectively; Table 1)” Ozone concentration continues to increase at a similar rate under the RCP4.5 emission scenario, and RCP8.5 also will lead a worldwide increase to ozone due to the lack of emission regulation. So why are ozone concentrations at the similar levels under RCP4.5 and RCP 8.5? and ozone in the RCP4.5 is even slightly higher than that in the RCP8.5.
Citation: https://doi.org/10.5194/egusphere-2024-3371-RC1
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