Climate change impacts on agriculture and irrigation in the Lower Mekong Basin

According to hydrological simulations by the Mekong River Commission, average annual flow of the Mekong will not change significantly despite climate change. However, they projected increased variability in wet and dry season flows, which will tend to increase the flood and drought risks to crops. To learn the implications of climate change for rice farming in the Lower Mekong Basin (LMB), a lower part of the Basin from China-Lao PDR border to the South China Sea, climate and hydrological figures related to rice production were compared in between the baseline in 1985–2000 and the climate change scenario in 2010–2050. Special attention was given to their 10 and 90 % exceedance values, which are rough equivalence of 10 and 90 % cumulative probabilities, to see changes in the frequency and extent of extreme weather events. Major findings of this study include the followings: (1) evapo-transpirations will increase in both average and 90 % cumulative probability values, raising irrigation demand. (2) Deviation of the annual rainfall will become larger, causing water shortage in reservoirs more frequently in the future. (3) The transplanting date of rain-fed rice will be delayed more likely due to insufficient precipitation in the early wet season, which may result in decreasing rice production. (4) Longer dry spells will be observed during the wet season, raising the drought risk to rain-fed rice. (5) These changes will be generally observed across the LMB, while the extent of the changes varies among regions.

     

Impacts of climate change on rice market and production capacity in the Lower Mekong Basin

The supply of water is affected by climate changes. In addition, high economic growth in the lower Mekong River countries including two large rice exporters is expected to reduce the per capita consumption of rice as incomes grow. Consequently, the need exist to investigate changes in supply and demand using econometric models of rice markets in the countries, where water supplies are expected to change. The objective of this research is to clarify impacts of water supply changes on rice producers and consumers using supply and demand models of rice considering changes in the water supply to aid in producing agricultural policies and plans. The following two simulations were conducted in this assessment: (a) baseline and (b) CC_B2. The simulation of the baseline includes the assumption that the evapotranspiration (ET) of each province after 2000 is the average quantity of ET from 1995 to 1999. The simulation of the CC_B2 includes the assumptions that ET of each province after 2010 accords with the IPCC socioeconomic scenario B2. The simulation results suggest that climate change will depress wet season rice production in Cambodia and Mekong River Delta (MRD) region in Vietnam, and that of dry season rice in the MRD region in Vietnam and northeastern region (Isan) Thailand. The simulation results also indicate that climate change will increase farm prices of rice in Cambodia, Vietnam, and Thailand. The results suggest that climate changes will weigh on the livelihood of rice consumers, especially those of poor rural populations.

     

Impacts of climate change on rice market and production capacity in the Lower Mekong Basin

The supply of water is affected by climate changes. In addition, high economic growth in the lower Mekong River countries including two large rice exporters is expected to reduce the per capita consumption of rice as incomes grow. Consequently, the need exist to investigate changes in supply and demand using econometric models of rice markets in the countries, where water supplies are expected to change. The objective of this research is to clarify impacts of water supply changes on rice producers and consumers using supply and demand models of rice considering changes in the water supply to aid in producing agricultural policies and plans. The following two simulations were conducted in this assessment: (a) baseline and (b) CC_B2. The simulation of the baseline includes the assumption that the evapotranspiration (ET) of each province after 2000 is the average quantity of ET from 1995 to 1999. The simulation of the CC_B2 includes the assumptions that ET of each province after 2010 accords with the IPCC socioeconomic scenario B2. The simulation results suggest that climate change will depress wet season rice production in Cambodia and Mekong River Delta (MRD) region in Vietnam, and that of dry season rice in the MRD region in Vietnam and northeastern region (Isan) Thailand. The simulation results also indicate that climate change will increase farm prices of rice in Cambodia, Vietnam, and Thailand. The results suggest that climate changes will weigh on the livelihood of rice consumers, especially those of poor rural populations.     

Assessment of irrigation efficiencies and water productivity in paddy fields in the lower Mekong River Basin

Improving irrigation performance is a crucial issue for agriculture and irrigation development in the Lower Mekong River Basin to secure food production for people’s livelihoods. Irrigation efficiency is the most important indicator to determine the performance of an irrigation scheme. This study looks at water management practices and irrigation efficiency in three pilot sites in the Lower Mekong River Basin: the Numhoum scheme in Laos, the Huay Luang scheme in Thailand, and the Komping Pouy scheme in Cambodia. Irrigation efficiency and water productivity were analyzed using a water balance approach at the irrigation scheme level and results in the pilot areas show efficiencies that are definitely higher using this approach than by using the classical concept. Lower water productivity was observed at pilot schemes in areas of single cropping and higher productivity in areas where multiple agricultural activities were practiced. Strict and active water management is required to control and save water to meet agricultural demand and have sufficient water to expand cultivation areas while avoiding shortages. Promoting multiple uses of water for various agricultural activities in command area will increase water productivity.

长江流域不同种植区气候因子对冬油菜产量的影响

气象因子对长江流域油菜（Brassica napus L.）主产区影响很大。为明确长江流域影响油菜生长的关键气象因子,基于长江流域259个气象站1961-2015年的气象数据及1437个田间试验冬油菜产量数据,分析5个不同区域（长江上游低海拔区、长江上游高海拔区、长江中游二熟区、长江中游三熟区和长江下游）冬油菜生育期内气候因子的时空分布特征,结合产量数据分析不同种植区油菜产量的气候限制因子。结果表明：长江流域冬油菜生育期 内平均气温为13.2℃,≥0℃积温为3620℃,昼夜温差7.8℃,总日照时数984h,太阳辐射量为2631 MJ·m-2。油菜生育期内热量资源呈现增加的趋势,平均气温每10年升高0.37℃,而昼夜温差每10年缩小0.21℃;而日照资源则逐年降低,每10年日照时数降低45h。油菜全生育期总降水量平均为680 mm,且呈现逐年增加的趋势。长江流域气象因 子与油菜产量的关系主要表现为：平均气温和≥0℃积温与产量呈现负相关关系,其中长江中游二熟区生育前期（9 月-11月）和长江中游三熟区生育后期（3月-5月）平均气温每增加0.1℃,油菜分别减产53和40 kg·hm-2;昼夜温差大有利于油菜增产,其中长江上游低海拔区后期昼夜温差每增加0.1℃,产量增幅为39 kg·hm-2;降水量与产量主要呈现负相关关系,尤其是后期降水量每增加10 mm,油菜减产约12～39 kg·hm-2。从整个生育期来看,长江上游（低海拔区、高海拔区）主要影响油菜产量的气象因子为昼夜温差、降水量和日照时数;长江中游二熟区主要受气温、积温、降水量和太阳辐射的影响;长江中游三熟区的限制因子为气温和积温;而长江下游则受到降水量、日照时数和太阳辐射的影响。     

Operation of the Ba Lai irrigation system in the Mekong Delta, Vietnam

Ba Lai Irrigation Project is located at coastal area in the Mekong Delta. In dry season when the flow rate decreases and the strong east wind blows into the delta, the salinity intrusion increases and seriously affects agricultural and domestic water use. Intakes of Ba Lai system have to be closed for 1–3 months depending on their locations, and no water supply during this period often causes water pollution in the project area. In order to solve such problems, this study aims to seek gate operation procedures for salinity control and water environment improvement. A numerical model is developed to simulate water movement, salinity concentration and duration of remaining water (water age) within the system under three scenarios: (1) without control structures, (2) with available control structures, (3) with the full control structures. Through the numerical simulations, control structures are confirmed to be an effective measure for the salinity control and suitable gate operation schedules are proposed to improve the water environment in the project.     

Future potential impacts of climate change on agricultural watershed hydrology and the adaptation strategy of paddy rice irrigation reservoir by release control

This study is to assess the climate change impact on the temporal variation of paddy rice irrigation reservoir water level from the future evaluated watershed inflow, and to suggest an adaptation method of the future reservoir water level management for stable water supply of paddy irrigation demands. A 366.5 km² watershed including two irrigation reservoirs located in the upper middle part of South Korea was adopted. For the future evaluation, the SLURP model was set up using 9 years daily reservoir water level and streamflow records at the watershed outlet. The average Nash-Sutcliffe model efficiencies for calibration and validation were 0.69 and 0.65, respectively. For the future climate condition, the NIES MIROC3.2 hires data by SRES A1B and B1 scenarios of the IPCC was adopted. The future data were downscaled by applying Change Factor statistical method through bias-correction using 30 years past weather data. The results of future impact showed that the future reservoir storages of autumn and winter season after completion of irrigation period decreased for 2080s A1B scenario. Considering the future decrease of summer and autumn reservoir inflows, the reservoir operation has to be more conservative for preparing the water supply of paddy irrigation, and there should be a more prudent decision making for the reservoir release by storm events. Therefore, as the future adaptation strategy, the control of reservoir release by decreasing in August and September could secure the reservoir water level in autumn and winter season by reaching the water level to almost 100% like the present reservoir water level management.     

Factors impacting yields in rain-fed paddies of the lower Mekong River Basin

The Mekong River Basin (MRB) is the biggest basin in Monsoon Asia. About 80% of the agricultural lands, which occupy about 40% of the basin are rain-fed paddy rice area. Therefore, it is assumed that changes in rain-fed paddy rice production affect the total agricultural production to a great degree in the Mekong River Basin. While there are many factors affecting the productivity of rain-fed paddies, such as climate, water use, rice varieties, applications of manure, fertilizer and agro-chemicals, sowing date and other agronomic practices, this paper focuses on the relation between rainfall and yields of rain-fed paddies. Agricultural statistics and rainfall data were collected and analyzed for all 24 provinces in Cambodia for the years 2001 and 2002. Factors such as soil fertility and other natural conditions were removed by comparing the yield and rainfall in one province for different years. Special attention was given to the relation between yields of paddy in the wet season and rainfall, considering factors such as rice varieties, soil fertility, irrigation ratio and the ratio of area damaged by flood, drought, and insect. Although it is not easy to assess those impact factors on yields because they are organically interactive, the following results were obtained: (1) The ratio of high yielding varieties (HYV), soil fertility, and irrigation ratio among many factors that affect yields individually, especially if they are combined, (2) Total rainfall did not have a significant influence on rice yields even for the rain-fed paddies if it was over 700 mm in wet season, and one of the reasons for this would be that there exist supplementary water uses through small ponds and water ponding in local land depressions in and around paddies.     

Wildlife pests of California agriculture: Regional variability and subsequent impacts on management

Numerous wildlife species are known pests of California agriculture. Effective management of these pests is required to maximize agricultural production, yet it is unclear how the importance of various wildlife pest species and associated management strategies may vary regionally throughout California. Accounting for these regional differences should yield management programs that are specifically tailored to the regions constituents and should be considered when managing wildlife pests at a more localized level. Therefore, we developed a survey to provide quantitative data on regional differences in research and management needs to better guide future research efforts in developing more effective, practical, and appropriate methods for managing wildlife pests. We found that coyotes were a more common pest in the mountain region, ground squirrels were a greater concern in the central and desert valley region, while birds were most commonly listed as pests by individuals working in multiple regions of California. Coyote damage varied regionally, with livestock depredation the greatest concern throughout most of California, although damage to irrigation tubing and sprinklers was of equal concern in the central and desert valley region. For bird pests, exclusionary devices were the most common and most effective methods of control in the coastal region. Frightening devices were the most commonly used method for bird control in all other regions, although the efficacy associated with frightening devices was considered far lower than their level of use, suggesting that better management options are needed for bird control in these regions. For all wildlife pests, nonlethal control options (e.g., exclusionary devices, habitat modification) were generally preferred in the coastal region while lethal removal options ranked higher in the central and desert valley region (e.g., baiting, burrow fumigation). Efficacy was considered the most important attribute of a control method for all regions, while Integrated Pest Management programs were considered the most effective method for controlling wildlife pests in all regions except for the central and desert valley region. Collectively, the importance of wildlife pests and the perception of associated control methods varied throughout California and reflects the need to consider these regional differences in order to optimize damage management strategies at the regional level.     

Climate change effects on paddy field thermal environment and evapotranspiration

The effect of air temperature increase from meteorological data on thermal microenvironment of irrigated paddy field is simulated using energy balance model. Statistical test was used to determine the existence of the trend in temperature change of data from meteorological stations in Indonesia. The temperature was tested to have positive trend, and it was used to generate future and past increase of temperature for the simulation. According to the simulation, the change in energy balance occurs following additional heat contributed by the increase of air temperature. The results show that irrigated paddy field seems to have function of decreasing effect of temperature increase whereas, evapotranspiration increases. However, increasing air temperature also increases temperature in paddy system, but seems to be more moderate than in nonpaddy field.     

Impact of climate change on paddy field irrigation in southern Taiwan

Climate change can have a serious impact on water resources. The main agricultural product in southern Taiwan is rice, the planting of which consumes far more water than other crops. This makes agriculture in Taiwan especially vulnerable to climate change. In this study, we used the generalized watershed loading functions (GWLF) hydrological model to simulate the discharge of the Kaoping River under climate change scenarios A2 and B2 as released by the Intergovernmental Panel on Climate Change. We discussed the potential impact of climate change on water resources based on the results of GWLF simulations carried out using rainfall and temperature data from five general circulation models (GCMs). The simulation results indicate that river discharge in the wet season increases significantly, and decreases in the dry season. The discharge variations from using the various GCMs as inputs fall within the range of ?26 to +15 % for the dry season and ?10 to +82 % for the wet season. The variation in available water will seriously impact the first period rice farming (the period between the beginning of January and the end of May) in southern Taiwan. Consequently, effective reduction in conveyance loss in the irrigation canal systems and proper fallowing of paddy fields will be the main challenges to Taiwan’s agricultural sector for alleviating the impact of climate change. For further decision making, we show the effects of adapting to climate change by various degrees of the following two methods: fallowing paddy fields to various degrees and reducing conveyance loss in irrigation canal systems.     

Potential impacts of climate change on patterns of production and the role of drainage in grassland

Grass production can be predicted using a simple model whose inputs include daily meteorological variables. Changes in both daily temperature and the soil water balance can be expected as a consequence of anthropogenic increases in the CO₂ content of the atmosphere. Possible consequences of such changes for grass production are then predicted using the model. These indicate that, for the UK, patterns of grass production could be shifted significantly. Greater grass growth in the spring would follow from the increase in temperature, particularly on drained land where growth is not constrained by water logging. However, grass growth would be depressed by the mid-season soil moisture deficit, and this again is more marked on drained land, it is concluded that, under a changed climate, the drainage of grassland to enable early season access to the land, together with sound management to optimize output, will be even more important than at present.     

Methodologies for simulating impacts of climate change on crop production

Ecophysiological models are widely used to forecast potential impacts of climate change on future agricultural productivity and to examine options for adaptation by local stakeholders and policy makers. However, protocols followed in such assessments vary to such an extent that they constrain cross-study syntheses and increase the potential for bias in projected impacts. We reviewed 221 peer-reviewed papers that used crop simulation models to examine diverse aspects of how climate change might affect agricultural systems. Six subject areas were examined: target crops and regions; the crop model(s) used and their characteristics; sources and application of data on [CO₂] and climate; impact parameters evaluated; assessment of variability or risk; and adaptation strategies. Wheat, maize, soybean and rice were considered in approximately 170 papers. The USA (55 papers) and Europe (64 papers) were the dominant regions studied. The most frequent approach used to simulate response to CO₂ involved adjusting daily radiation use efficiency (RUE) and transpiration, precluding consideration of the interacting effects of CO₂, stomatal conductance and canopy temperature, which are expected to exacerbate effects of global warming. The assumed baseline [CO₂] typically corresponded to conditions 10-30 years earlier than the date the paper was accepted, exaggerating the relative impacts of increased [CO₂]. Due in part to the diverse scenarios for increases in greenhouse gas emissions, assumed future [CO₂] also varied greatly, further complicating comparisons among studies. Papers considering adaptation predominantly examined changes in planting dates and cultivars; only 20 papers tested different tillage practices or crop rotations. Risk was quantified in over half the papers, mainly in relation to variability in yield or effects of water deficits, but the limited consideration of other factors affecting risk beside climate change per se suggests that impacts of climate change were overestimated relative to background variability. A coordinated crop, climate and soil data resource would allow researchers to focus on underlying science. More extensive model intercomparison, facilitated by modular software, should strengthen the biological realism of predictions and clarify the limits of our ability to forecast agricultural impacts of climate change on crop production and associated food security as well as to evaluate potential for adaptation.     

The impacts of the water quality of the inflow water from tea fields on irrigation reservoir ecosystems

Authors observed that the nitrate nitrogen (NO₃-N) concentration is approximately 30 mg/L and that the average pH value is 4.3 in a small river in Shizuoka Prefecture, Japan. Further, when there is heavy rain, the pH value of the river water decreases to below 3.5 at times. There is a small irrigation reservoir in the watershed. The reservoir receives this water and mixed with other river water, the pH in the reservoir reaches below 5.0 at times, making it impossible for fauna to survive there. This water is also used for paddy irrigation, however no damage to rice production was reported. The authors clarified the fact that the low pH and high NO₃-N concentrations were brought about by the overuse of nitrogen fertilizers in tea fields. Further, the authors proposed a model, which can be used to estimate the pH value and the NO₃-N concentration.     

Individual lift irrigation: a case study in the Cau Son irrigation and drainage area, Red River Basin, Vietnam

The irrigation trend in Asia has been characterised as a shift from gravity to lift irrigation, but the importance of individual lift irrigation using surface water remains to be documented. Surveys on field water application by farmers using lift were undertaken in three sites and across the 44,600 ha Cau Son irrigation and drainage area in the spring crop season. Lift irrigation was found to be practised by 82 % of households. The main lift technology was mechanical pump (petrol and electric), followed by traditional swing and long-handle baskets. The main source for lifting was on-farm canals. Although gravity irrigation was the dominant field application method, the area solely irrigated by individual lift ranged from 25 to 52 % of the irrigated areas. Scaling up from the sites, individual lift accounted for 29 % by irrigation area and volume, with 17 and 12 % attributed to mechanical and manual lift. The application of mechanical pumps was a response to locally high-field elevations and significantly increased with the distance of water delivery from the main canal. The impact of mechanical pumping on flexibility and reliability was significant and positive. Petrol driven pumps had relatively high operational and investment costs, but farmers gained higher flexibility and reliability and compensated by applying less water. Farmers using electric pumps applied significantly more water and thereby wasted electric energy as a compensation for uncertain electric power supply. The importance of individual lift irrigation suggests that it should be explicitly considered in irrigation management policies and performance assessments.     

Influence mechanism of climate change on paddy farming practices and irrigation water demand

Paddy and Water Environment - Technological and socioeconomic interventions accompanied by climate warming strongly dictate farming practices, lending a direct impact over future irrigation water...     

近三十年来厦门市气候的变化

依据厦门市1971—2004年34年的基本气象资料,研究分析了该市年均气温和年降水量的年际变化特征,并确定了各自的气候突变点,据此分析了该市的气候类型。结果表明：（1）从20世纪80年代以来,该市年均气温以每年0．0631℃的速度在升高,年均气温出现2个气候突变点,分别为1981和1998年;（2）年降水量多年变化趋势不明显,呈随机变化,年降水量出现2个气候突变点,分别为1977和1990年;（3）34年的气候类型分为暖湿、暖干、冷湿和冷干4种类型。     

气候及其变率变化对长江中下游稻区水稻生产的影响

 在长江中下游稻区选择19个样点,将每个样点近20年（1979-1998年）的水稻产量资料及同期气象资料分为两组,一组结合当地水稻生态试验或品种区域试验资料用于CERES Rice模型中遗传参数的调试,另一组用于检验该模型在研究区域的适用性。通过对未来气候变率变化(ΔCV)的3种假设并利用WGEN(天气生成器),将每个样点基于3种平衡GCM(大气环流模型)的CO2倍增气候变化情景文件改进为兼顾气候及其变率变化(CC+ΔCV)的9种情景文件。在上述各情景文件下分别运行CERES Rice,并将模拟结果与本底气候 (Baseline)下的模拟值进行比较,再结合蒸散比（β）和产量波动系数等算法,评价了CO2有效倍增时CC+ΔCV对长江中下游稻区水稻生产的影响。结果表明,当CO2有效倍增时,随着ΔCV的增大,不同稻作制度下水稻高温热害将愈演愈烈,早稻和晚稻受低温威胁将显著减轻;水稻生长季内干湿状况较目前无明显差异,但季节性干旱和暴雨的发生频次呈增加之势;研究区域不同稻作制度下的水稻生育期均明显缩短,ΔCV增大对生育期无显著影响;不论是单、双季稻,还是灌溉或雨育水稻都显著减产,其中中游稻区的减产幅度大于下游稻区,单季稻和晚稻的减产幅度大于早稻,UKMO、GISS情景下的减产幅度大于GFDL情景;研究区域不同稻作制度下的水稻进一步减产,且稳产性变差,但良好的灌溉条件可以减缓水稻产量的年际波动。