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Below is the data related to rain-fed maize under the SSP585 scenario under CNRM-CM6-1 |
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Dear Dr. Fridman, Thank you for your prompt reply. I would like to provide some references I have consulted in my research: [1] Jägermeyr, J., Müller, C., Ruane, A.C., et al. "Climate impacts on global agriculture emerge earlier in new generation of climate and crop models." Nature Food, 2, 873–885 (2021). This study utilizes agricultural models to simulate future crop yields using CMIP6 climate data from the ISIMIP3b rounds. It reports a projected 25% decrease in maize yield under the SSP585 scenario. [2] Challinor, A., Watson, J., Lobell, D., et al. "A meta-analysis of crop yield under climate change and adaptation." Nature Climate Change, 4, 287–291 (2014). [4] This study provides a global analysis of projected impacts on crop yields based on data from the past four decades. In this study,Holding current growing regions fixed, area-weighted average yields are predicted to decrease by 30 – 46% before the end of the century under the slowest (B1) warming scenario and decrease by 63– 82% under the most rapid warming scenario (A1FI) under the Hadley III model. It is important to note that these studies generally use crop calendars, with different planting and maturity dates for each location. For the United States and China, maize planting periods typically range from April to October, which aligns with the period I have selected. However, there are still significant discrepancies with other research findings. Thank you again for your assistance. Best regards, |
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I have used the following formula to represent the sensitivity of the factors: |
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Dear @whq552800 Thank you for your elaborated response. It looks like you have done a through exploration of the literature, well done. Unfortunately, I could not go in depth into all the citation you have presented. What I do see (particularly in the first two papers) is quite large uncertainty and disagreement between the models, showing a decrease for maize (relative to the the present) that ranges between 10%-25% (second one, and can be much below 30% for the first paper. One major point I have noticed. I suspect you may mis-use CWatM crops' functionality. The module primary aim is to provide a better estimation of plant water requirements affecting soil moisture and irrigation demand. To get the change in future yield relative to the past you would have to obtain potential yields under full irrigation (e.g., from GAEZ: https://gaez.fao.org/) for the past and future, calculate actual yield for both period and only than calculate the relative change, as: future_yield / past_yield - 1. Hope this would help you somehow. |
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Dear Dor Fridman, |
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Dear @whq552800 No worries. We are happy to help CWatM's users community. The model is complex and constantly improving, thus it may be challenging to keep track. Best |
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I am attempting to use CWatM to simulate future crop yields. I have followed steps from a YouTube tutorial ’https://www.youtube.com/watch?v=YvdVTB4wtTA&t=397s‘, and I am using mapspam data. To simplify the computation, I applied a uniform date globally.
The resolution is set at 30 arcminutes. The following outputs were generated: OUT_MAP_AnnualTot = actTransTotal_month_nonIrr, Yield_Irr, Yield_nonIrr, crop_eta_nonirr, crop_eta_irr, ratio_a_p_nonIrr, ratio_a_p_Irr, crop_pet_irr, crop_Precipitation, crop_Tavg.
Some of the variables in it are edited by me according to my personal needs.
To obtain results for each crop, I modified the code for internal model output in the “output.py” file. Details of the modification can be found in the attached image.
Based on existing research, maize (corn) is the crop most responsive to future climate changes among the four crops studied. Additionally, the area of irrigated maize in the mapspam data is very small, so I focused on analyzing rainfed maize. However, the results I obtained show a yield decline of approximately 6%(Scenario:SSP585, variable: Yield_nonIrr_annualtot_MAIZ, I used the mean of the variables in the last 30 years (2070-2100) to compare the changes in the first 10 years (2020-2030)), which is much lower than the 30% decline reported in published papers. I am unsure where the issue lies.
The picture below shows the interannual variation of rain-fed maize.
P.S.: The mapspam dataset includes crop yield data, and I am considering calculating future yields by taking the ratio of the annual relative crop yield (Yr) to the Yr from the most recent year (2019) obtained using GWSP3-W5E5, and then multiplying this ratio by the yield values in the mapspam dataset. Would this approach be appropriate?
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