As the most widespread natural hazard, drought has significant impacts on the livelihood and ecosystems in the Lancang-Mekong River Basin (LMRB). However, few studies focus on the seasonal characteristics of drought in the LMRB, especially under future climate projections by the Sixth Phase of Coupled Model Inter-comparison Project (CMIP6). This study filled the knowledge gap using SPI and SPEI, based on eight GCMs of CMIP6 under three scenarios (i.e., SSP1-2.6, SSP2-4.5, SSP5-8.5). Our results show that the LMRB tends to experience wetter wet season and drier dry season with the rising temperature considered (based on SPEI), while the temporal trend of dry-season SPI is not significant. The future trends of SPEI are -0.006 per year and -0.011 per year under SSP2-4.5 and SSP5-8.5, respectively. The trend magnitudes demonstrate spatial heterogeneities. Our evaluation based on SPEI shows that the most notable increases of dry-season drought (in terms of duration and intensity) are distributed in the middle reaches of LMRB. The upper Lancang and middle Mekong basin will likely experience more wet-season droughts. The dry-season drought accounts for 60% of total drought events in the near future (i.e., 2021–2055) and more than 80% in the far future (i.e., 2061–2095) under SSP2-4.5. Effective strategies are needed to enhance food and drinking water security in the LMRB, especially for the dry seasons under a changing climate. 

Future projection of seasonal drought characteristics using CMIP6 in the Lancang-Mekong River Basin

Barnyardgrass (Echinochloa crus-galli(L.) Beauv.), an annual species of the family Poaceae, is a major weed problem in rice-producing countries throughout the globe. Synthetic herbicides can effectively control this grass in rice paddies, but the development of resistant biotypes after the continuous use of the same active ingredients has led to low herbicide efficacy and yield losses. In this review, a summary of resistant-barnyardgrass cases in global rice production is reported based on data from the International Herbicide-Resistant Weed Database. The first case of resistant barnyardgrass in rice paddies was to the photosystem-II inhibitor propanil in the late 1980s. Eighty-five (85) out of 116 cases in the period from 1986 to 2022 refer to resistant barnyardgrass (E. crus-galli var. crus-galli, E. crus-galli var. formosensis and E. crus-galli var. zelayensis) in 16 countries. Barnyardgrass has been found resistant to acetolactate synthase (ALS) inhibitors (34 cases), acetyl-CoA carboxylase (ACCase) inhibitors (23 cases), photosystem-II inhibitors (11 cases), auxin mimics/cellulose biosynthesis inhibitors (9 cases), very long chain fatty acid inhibitors (6 cases), and microtubule assembly inhibitors (1 case). The majority of all resistance cases reported to the active ingredients penoxsulam, bispyribac-sodium, and imazamox (ALS inhibitors), cyhalofop-butyl and fenoxaprop-ethyl (ACCase inhibitors), propanil (photosystem-II inhibitors), and quinclorac (auxin mimics/cellulose biosynthesis inhibitors). Although target-site resistance with specific mutations has been identified, non-target site resistance mainly through herbicide detoxification is also of great concern increasing the chance of multiple herbicide resistance evolution. Rotation of herbicides should be adopted concerning the modes of action used as well as the application methods to mitigate resistance evolution of this weed in rice paddies. 

Herbicide‐resistant barnyardgrass (
 
 Echinochloa crus‐galli
 
 ) in global rice production

Irregular rainfall, rising temperatures and changing frequency and intensity of extreme weather events are projected to reduce crop yields and threaten food security across the tropical monsoon sub-region. However, the anticipated extent of impact on crop yields and crop water productivity (CWP) is not yet thoroughly understood. The impacts of climate change on rice yields and CWP are assessed over the Northern Tonle Sap Basin in Cambodia by applying the AquaCrop model into the mid- (2041–2070) to long- (2071–2099) future under two Representative Concentration Pathways (RCPs) (4.5 and 8.5). Short (95 days), medium (125 days) and long (155 days) cycle varieties are tested during the wet and dry seasons. An assessment of different sowing dates and irrigation strategies (fixed and net irrigation during the dry season) elucidated the variation in response to changing environmental conditions. Higher yields (+15% by 2041–2070 and +30% by 2071–2099) and CWP values (+42% by 2071–2099) are expected if using short-cycle varieties, in particular when sown in July. Dry season rice yields are also projected to increase (+28% by 2071–2099) and higher yields are simulated under a higher greenhouse gas emission scenario (RCP 8.5) compared with a medium emission scenario (RCP 4.5) as a result of the CO2 fertilization effect. Depending on the climatic scenario, rice variety, irrigation scheme, and sowing date, increasing heat and drought-stress conditions are likely to have different impacts on rice yields and CWP over time. Overall, this study highlights the benefits of adjusting crop calendars to identify the most suitable irrigation schedules and rice variety to effectively adapt to projected future climate. 

https://repositorio.unican.es/xmlui/bitstream/10902/26957/3/ModellingClimateChange.pdf

Modelling climate change impacts on wet and dry season rice in Cambodia

https://doi.org/10.1016/j.heliyon.2023.e15480

Modelling climate variabilities and global rice production: A panel regression and time series analysis

Abstract This study evaluates the effects of climate change (CC) on runoff properties over the case study of the Qaran Talar watershed located in Iran. To consider the two main sources of uncertainty, i.e., Greenhouse Gases emission (GHG) scenarios and outputs of Atmosphere-Ocean General Circulation Models (AOGCMs), a daily rainfall time series was generated for two future periods (2021-2050 and 2070-2099) at three risk levels of 0.1, 0.25 and 0.50. 22 AOGCMs outputs following two emission scenarios (RCP4.5 and RCP8.5) were used. The results showed that the uncertainty of climate change scenarios was primarily owing to the uncertainty of GCMs outputs. Regarding the 2021-2050 period, under both emission scenarios, the increases in peak discharge and flood volume (FV) were estimated to reach 70, 50, and 30% at three risk levels of 0.1, 0.25 and 0.50, respectively, compared to the recent past period. As the current century draws to a close, the difference between the results of the two emission scenarios becomes apparent so that in the far-future period (2070-2099), the RCP8.5 scenario estimates and FV more than the RCP4.5 scenario does. Additionally, it was found that the uncertainty caused by AOGCMs was more than that by GHG emission scenarios. 

Evaluating uncertainty in climate change impacts on peak discharge and flood volume in the Qaran Talar watershed, Iran

Quantifying the GCM-related uncertainty for climate change impact assessment of rainfed rice production in Cambodia by a combined hydrologic - rice growth model

T. Ohta

Papers

Quantifying the GCM-related uncertainty for climate change impact assessment of rainfed rice production in Cambodia by a combined hydrologic - rice growth model