Journal of Agricultural Meteorology最新文献

　Climate change is increasingly being recognized as a potential threat to food security. This study assessed the risk of climate change on rice production value in the Tohoku and Kyushu regions. In a scenario without climate change mitigation, characterized by a 4 K global average temperature increase compared to pre-industrial levels, a significant decrease in rice production value was projected for Tohoku (93.9%) and Kyushu (75.9%). Based on the current value, each 1 K increase in temperature is estimated to result in an annual economic loss of approximately 7 and 12 billion yen in Tohoku and Kyushu, respectively. The frequency of losses in production value, which is typically expected to occur once every 25 years under current climate conditions, may occur more frequently (Tohoku: every 4.0 years; Kyushu every 1.1 years). This increased risk is attributed to a reduction in the proportion of first-grade rice, which is compounded by decreased yields in Kyushu. The negative trends become less pronounced when considering the mitigation efforts that limit the global temperature rise to 2 K. In this scenario, the decline in production value that occurs once every 25 years does not occur in Tohoku because of increased yields. In Kyushu, however, this decline still occurs once every 5.6 years, mainly because of a reduced proportion of first-grade rice in the total production. In both regions, increasing yield through earlier transplanting proved more effective in mitigating production decline than improving the proportion of first-grade rice through later transplanting, regardless of the extent of the temperature rise. With the current rice varieties and transplanting schedules, production decline is difficult to prevent under severe climate change conditions. Therefore, high-temperature-tolerant rice varieties must be promoted, and their transplantation must be adjusted to adapt to future environmental conditions.

　It is predicted that climate change will make the cultivation of satsuma mandarins more challenging unless adaptation measures can be implemented in current production areas, although changing conditions may favor the cultivation of subtropical fruit trees such as avocado. Therefore, we assessed suitable locations for the future cultivation of both tree species in Japan and the potential of avocado as a substitute for satsuma mandarin. Suitable locations were determined using the annual mean (satsuma mandarin) and minimum (both species) temperatures calculated from the projected temperatures based on two global climate models (MRI-ESM2-0 and MIROC6) under three shared socioeconomic pathways (SSP). Suitable locations for satsuma mandarins were predicted to move northward until the mid-21st century under SSP1-RCP2.6 or until the end of the 21st century under SSP2-RCP4.5 and SSP5-RCP8.5. Among the suitable locations for satsuma mandarins for 1990-2009, the percentage that remained suitable for 2080-2099 varied depending on the SSP, ranging from 0% (SSP5-RCP8.5) to approximately 80% (SSP1-RCP2.6). This highlights the substantial impact of climate change mitigation measures on current satsuma mandarin production areas. Suitable locations for avocados were projected to certainly expand definitely in the future, regardless of the SSP, and many of the suitable locations for satsuma mandarins for 1990-2009 will become suitable for avocados for 2040-2059. Because temperature conditions are suitable for avocado cultivation in most locations that will become too warm for satsuma mandarin production in the future among the suitable locations for satsuma mandarin for 1990-2009, replanting from satsuma mandarins to avocados is an adaptation option in current production areas. Although adaptation measures using cultivation techniques and high-temperature-tolerant cultivars are likely to become less effective as climate change progresses, replanting to avocados was shown to be an effective alternative, at least until the end of the 21st century.

　Elevated temperatures during the flowing stage can induce spikelet sterility in rice, posing a major threat to production under climate change. Projecting the impacts and developing effective strategies are critical, but our understanding of regional, seasonal, and long-term trends in rice heat exposure remains limited. Previous studies on spikelet sterility revealed that panicle temperature, estimated using a micrometeorological model and common meteorological factors, serves as a reliable indicator of rice heat exposure. In this study, we employed this model to identify the temporal and spatial variation of panicle temperatures, the differences between panicle and air temperatures (DPAT), and their causes over the past 45 years in Japan. A gridded daily meteorological dataset covering Japan was interpolated at an hourly time step and used as input data of the micrometeorology model for estimating panicle temperatures. Before 2000, estimated panicle temperatures around the heading stage, the most susceptible stage to heat, had rarely exceeded the critical threshold of 33°C, but the heat exposure frequency above this threshold (HEF) has increased almost exponentially in multiple regions since then, increasing the risk of heat-induced sterility. In the unprecedentedly hot summer of 2023, the mean HEF in the Kanto and Chubu regions exceeded 30%. In most regions in Japan, panicles were estimated to be warmer than air, indicating the inadequacy of relying solely on air temperature to gauge rice heat stress. DPAT values showed substantial inter-regional variations in both mean values (from －0.5°C to 3.0°C) and seasonality. Through machine learning and statistical methods, the relationship between DPAT and meteorological factors was characterized, delineating the effects of the meteorological factors on regional and seasonal DPAT variations. Focusing on major high-risk regions, we show that mitigation strategies should be adapted to consider regional characteristics and avoid high panicle temperatures and DPAT conditions during rice heading periods.

　To evaluate suitability for growth of tropical fruits under global warming in Japan, we revealed cold tolerance threshold of subtropical fruit trees by performing field and chamber experiment and developed an extrapolatory method that can predict the cold tolerance of subtropical fruit trees without conducting extensive field experiments. Results of the field experiments estimated cold tolerances of -1.5 and -2°C for ‘Summer Queen’ passion fruit and ‘Sata’ lychee, respectively, and -5, -4.5, and -4°C for ‘Mexicola,’ ‘Bacon,’ and ‘Fuerte,’ avocados, respectively, indicating the dependence of cold tolerance on the variety of the tree species. The cold tolerance obtained from the field experiment was higher than the chamber experiment by 1°C for passion fruit and avocado and 2°C for lychee, which is explained by the difference between air and leaf temperature of field trees caused by radiative cooling on a clear and calm night. Therefore, cold tolerances of passion fruit and avocado can be estimated by adding 1°C to the cold tolerances obtained from the chamber experiment and that of lychee can be estimated by adding 2°C to the cold tolerance obtained from the chamber experiment. Moreover, even for other tree species, which were not consider in this study, the cold tolerance of the trees grown in fields can be estimated based on the results of the chamber experiment and using estimations of the difference between air and leaf temperatures on a clear and calm night.

　Remotely sensed solar-induced chlorophyll fluorescence (SIF) is applicable as an indicator of changing photosynthetic activity in terrestrial ecosystems. The vegetation of Borneo has previously been affected by drought and fire during El Niño events. Changes in satellite-based SIF data during an El Niño event in Borneo in 2015 were examined using three satellites-GOSAT, GOME-2, and OCO-2-covering the whole island and its southern and northern areas, respectively. Relationships between environmental factors and vegetation damage, precipitation, fire incidence, vegetation indices, and gross primary production (GPP), which were determined using machine-learning methods, were also examined for the period 2007–2018. SIF tended to be low in dry seasons, even in normal years, possibly because of increased drought stress and/or a higher incidence of fires with less precipitation. During the dry season of 2015, there were significant reductions in SIF in southern Borneo where fires were frequent. Other vegetation indices and GPP were also lower. Serious drought conditions with frequent fires during the El Niño event might have caused ecological degradation throughout Borneo, with a significant decrease in SIF.

　Tropospheric ozone (O₃) is known to harm crops by intrinsically affecting photosynthesis and other functions during crop growth. In staple crop production bases in the North China Plain (NCP) and Yangtze River Delta (YRD) regions, food security, especially food production, has been reported to be threatened by high O₃ concentrations. Studies have been conducted in the NCP or YRD to understand tropospheric O₃ and its precursor gases; however, the need to understand the effect of O₃ on crops in conjunction with the contributions of precursor gases (VOCs and NO_x) to O₃ formation using a fine-scale model remains. In this study, the combined Weather Research and Forecast with Chemistry (WRF-Chem) model was used to evaluate the impact of surface O₃ on reduced grain yield in China in 2010, covering the crop-growing seasons of single rice, double late rice, and winter wheat. The relative yield loss due to O₃ damage was evaluated using the accumulated O₃ exposure over a threshold of 40 ppb (AOT40) and a mean 7-hour O₃ mixing ratio (M7). The validation showed that the gas-phase chemistry mechanism Model for Ozone and Related chemical tracers, version 4 (MOZART-4), coupled with the Goddard Chemistry Aerosol Radiation and Transport (GOCART) aerosol module registered in WRF-Chem, can simulate O₃ fairly in the NCP and YRD. The aggregated average rice (wheat) relative yield losses throughout NCP and YRD were estimated to be 5.9% (27.1%) for AOT40 and 2.2% (9.6%) for M7, whereas aggregated rice (wheat) production losses were 2,345 kt (13,947 kt) for AOT40 and 999 kt (3,753 kt) for M7. In addition, reducing anthropogenic emissions of Volatile Organic Compounds (VOCs) from the energy and transport sectors is effective in reducing the surface O₃ concentration. The results provide important scientific evidence for achieving sustainable food production in China.

　To drive LEDs for plant cultivation using an alternating-current (AC) power supply, full-wave rectification (FWR) is a reasonable method to supply a unidirectional forward current to LEDs because of the simple configuration and low energy loss of the rectification circuit. We grew cos lettuce hydroponically using a white LED light source that emitted continuous light, 100 Hz square-wave (SW) pulsed light, or pulsed light generated with FWR of 50 Hz sine-wave AC with the same averaged photosynthetic photon flux density of 150 µmol m^-2 s^-1. The results showed that shoot fresh weight, shoot dry weight, leaf area, and number of leaves did not differ significantly among the treatments. Plants grown under FWR pulsed light showed similar net photosynthetic rates under continuous light and SW pulsed light. Shoot fresh weight per power consumption was estimated to be significantly greater with FWR pulsed light than with continuous light, and we concluded that the use of FWR pulsed light without elaborated transformation to a flat waveform direct current is a promising lighting method to reduce the lighting cost.

　In this study, we developed a method for evaluating the heat insulation capacity of breathable thermal screens. Heat transfer through breathable thermal screens involves radiation, convection, conduction, and ventilation. Of these, ventilation heat transfer is unique to breathable thermal screens, and warrants further understanding. Therefore, we evaluated the heat insulation capacity of aluminized (Screen_Al) and polyester (Screen_Poly) thermal screens. Ventilation heat transfer coefficient (k_ven), heat transfer coefficient of the nonventilated part of the thermal screen (k), and heat transfer coefficient including all heat transfer forms (k_all) were measured via a hot-box with heat balance analysis. The k_ven of Screen_Al (1.5 W m^-2 °C ^-1) was higher than that of Screen_Poly (1.3 W m^-2 °C^-1) because the ventilation rate of Screen_Al (4.2 m³ m^-2 h^-1) was higher than that of Screen_Poly (3.8 m³ m^-2 h^-1). The k of Screen_Al (4.1 W m^-2 °C ^-1) was lower than that of Screen_Poly (6.0 W m^-2 °C ^-1) because of the higher longwave radiation reflectance of Screen_Al. Finally, the k_all of Screen_Al (5.7 W m^-2 °C ^-1) was lower than that of Screen_Poly (7.2 W m^-2 °C ^-1). In conclusion, we successfully demonstrated a method by which the heat insulation capacity of breathable thermal screens can be evaluated.

　To enhance the study of sunburn and fruit surface temperature (FST) prediction in domestic fruit trees, we examined the spatiotemporal characteristics of FST and the predominant factors influencing FST on clear summer days by measuring the FST of detached apple and satsuma mandarin fruits, and monitoring ambient summer meteorological condition. With respect to the diurnal variation in FST, we found that the maximum FST of fruit (FST_max) occurred on the surface facing southwest to west, approximately 2 h post-meridian transit time, thereby indicating that compared with other orientations, the surface of fruit facing these directions is at higher risk of sunburn. Our observations also revealed that under clear conditions, the FST_max of apple and satsuma mandarin fruits can be at least 15°C above the daily maximum air temperature (AT_max). We also established that in addition to AT_max, fruit size plays a key role in determining FST. Furthermore, comparative black globes measurements also revealed that under clear conditions, a large black globe warmed to a greater extent than a similar smaller globe. Our findings in this study indicate that FST appears to be influenced by both fruit size and meteorological factors, using the data of which will enable precise FST predictions.