Study On Yield And Water Consumption Of Rice In The Lancang-Mekong River Basin Under The Influence Of Climate Change

Crop water consumption and yield are important areas of climate change impact,and increased climate change could have a significant impact on food production downstream of the Lower Lancang-Mekong River Basin.After the release of CMIP6’s future climate projection data,the study showed that the projections in many areas differed significantly from previous projections,making it necessary to study the response of water use and yield of rice,which is the main crop in the downstream of the Lancang-Mekong River Basin,to climate change,and serve regional policy development on climate change impacts.Based on data from the ERA5-Land dataset and the latest CMIP6 climate projection data,this study simulated historical and future rice yields and water consumption（total productive crop transpiration）in the Lower LancangMekong River Basin using the crop growth model AquaCrop model using three emission scenarios,i.e.SSP 1-2.6,SSP2-4.5,and SSP5-8.5.This study analyzed the changes of rice yield and water consumption in the downstream of the Mekong Basin,analyzed the correlation between rice yield and water consumption and temperature,precipitation,and carbon dioxide concentration,set up several scenarios to change meteorological elements,and quantitatively analyzed the response of rice yield to the change of each meteorological element.The main research results obtained are as follows.（1）Constructed the AquaCrop model for the lower reaches of the Lower Lancang-Mekong River Basin.Planting date,growing date,and harvest index（HI）of rice based on the measured rice yield and harvested area were calibrated and validated on a provincial basis,the AquaCrop model can be well adapted to the downstream of the Lower Lancang-Mekong River Basin.During the historical period,rice yields in the Lower Lancang-Mekong River Basin showed an increasing trend,with the highest historical average yield of 5.72 t/ha in Vietnam and the lowest average yield of 2.18 t/ha in Thailand.From the 1980s to the 2110s,rice growth in Cambodia,Laos,Thailand,and Vietnam was 15.2%,11.8%,17%,and 12.6%,respectively.（2）Based on the future climate simulation data from eight climate models,three scenarios,SSP1-2.6,SSP2-4.5 and SSP5-8.5,were used to simulate the future near-term and future far-term rice yields in the downstream of the Lower Lancang-Mekong River Basin.Compared with the historical period,rice production in the Lower Lancang-Mekong River Basin will increase in the future period,as shown by the yield growth in the SSP5-8.5 scenario is greater than that in the SSP2-4.5 scenario than that in the SSP1-2.6 scenario.From the historical period to the far future,the maximum increase in rice production in each country（Cambodia,Laos,Thailand,and Vietnam）can be 45.4%,28.8%,41.7%,and 34.6%.Rice yield and temperature showed a significant positive correlation in the near future,and rice yield responded significantly and positively to the increase in temperature.By the far future,this positive response continues to be maintained under the high emission scenario（SSP5-8.5）as temperature increases,and the continued increase in temperature under the low emission scenario（SSP1-2.6）will limit rice production with a significant negative correlation between rice yield and temperature.Rice yield and precipitation during the growing season mostly showed a significant positive correlation in the near future.In the far future,positive correlations between late-season rice yield and precipitation during the growing season were found in the SSP2-4.5 and SSP5-8.5 scenarios in Thailand and Vietnam,and the correlation between them was more significant in the SSP5-8.5 scenario.Overall,the correlation between rice yield and precipitation during the growing season is stronger in the near future than in the far future.（3）Based on the climate data of the historical period,four scenarios were set to adjust the minimum temperature,maximum temperature,precipitation and annual average CO₂ concentration to simulate rice yield,and the original data of the historical period was used to simulate rice yield as the baseline for comparison and analysis.Rice growth in the Lower Lancang-Mekong River Basin did not exhibit significant low temperature stress,but rice production is suffering from high temperature stress affecting rice yield in response to increasing global temperatures.The effect of a certain range of precipitation changes on rice yield was not significant,especially under conditions equipped with irrigation measures,and changes in precipitation did not lead to changes in rice yield.Compared to temperature and precipitation,the response of rice yield to changes in annual average CO₂ concentration was more pronounced,although the degree of response would be lower with increasing CO₂ concentration,but under certain conditions,CO₂ concentration was almost a determinant of rice yield.（4）Based on climatic data for the historical and future periods,water consumption for rice production in the Lower Lancang-Mekong River Basin was simulated for different scenarios over different periods.During the historical period,the average water consumption for rice production in Cambodia,Laos,Thailand,and Vietnam was 302.9 mm,347.2 mm,308 mm,and 258.8 mm,respectively.water consumption for rice production in the downstream of the Lower LancangMekong River Basin shows an overall decreasing trend,and spatially,water consumption for rice production shows less in the south and more in the north.（5）In the future period,water consumption for rice production in the Lower LancangMekong River Basin decreases relative to the historical period,and the reduction trend is more obvious under the SSP5-8.5 scenario,with Cambodia,Laos,Thailand and Vietnam reducing their water use for rice production by 28.9%,30.9%,25.5%and 38.8%,respectively,by the far future period.The reduction in water use for rice production in the future period was correlated with four climatic variables（minimum temperature,maximum temperature,precipitation,and CO₂ concentration）,with minimum and maximum temperatures showing positive correlations under the low-emissions scenario and rice water consumption for winter and spring plantings,and overall negative correlations under the remaining cropping systems.Correlation between water consumption and precipitation for winter-spring and late-season rice production in Vietnam is stronger than for other cropping systems.Rice production water consumption and CO₂ concentration under all cropping systems showed a significant negative correlation,with a correlation coefficient of-0.875 in Thailand in the far future under the SSP5-8.5 scenario and less than-0.9 in all seasons in the rest of the countries.