Uncertainty of paddy irrigation requirement estimated from climate change projections in the Geumho river basin, Korea

Despite evidence from numerous studies that over-reliance on a single General Circulation Model (GCM) could lead to inappropriate predictions or adaptation responses to climate change, single GCMs are still used in most mesoscale impact assessments. The objective of this article was to analyze the uncertainty associated with the use of multiple GCMs on future climate change impact assessments on the paddy irrigation water requirements in the Geumho river basin, Korea. Climate projections were extracted for 13 GCMs from the Intergovernmental Panel on Climate Change (IPCC) for A2, A1B, and B1 scenarios, downscaled using the change factor method and were then analyzed. The Food and Agricultural Organization CROPWAT model was used to calculate the paddy irrigation water requirements. Reference evapotranspiration and the crop water requirements were predicted to increase in future periods (2030s, 2055s, and 2090s). Rainfall predictions from the different GCMs exhibited high variability. The projected mean (range) of the paddy irrigation water requirement increase was 1.1% (?9 to 15%), 2.4% (?9 to 13%), and 7.9% (?4 to 24%) for the 2030s, 2055s, and 2090s, respectively, compared to the baseline values (1975s). The predicted irrigation water requirements for the future were shown to have a relative standard deviation of up to 7.1%. Regression analysis was performed on the trends of predicted water requirement over time using the coefficient of determination. It was concluded that multiple models should be used where possible to avoid inappropriate planning or adaptation responses particularly in the short term. Adaptation strategies are required to mitigate the future impact of increasing future water demand.     

A general adaptation strategy for climate change impacts on paddy cultivation: special reference to the Japanese context

Climate changes due to global warming may affect paddy cultivation considerably. Climate changes directly affect rice plant growth, and within paddy cultivation catchments, alter the hydrological regime including flood patterns and water availability for irrigation, and drainage. Although increased atmospheric CO₂ concentrations in the future may enhance plant growth through the CO₂ fertilization effect, impacts of climate change on agriculture are complicated and difficult to predict precisely. This is especially the case for assessing impacts on paddy cultivation, where basin hydrological behavior needs to be understood in detail. Possible adaptations to reduce negative impacts should be tailored to local conditions, which modify climate change impacts on paddy cultivation. In this article, climate change impacts on paddy cultivation are reviewed and a general adaptation strategy is discussed with special reference to the Japanese context.     

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.     

Evapotranspiration,irrigation water requirement,and water productivity of rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) in the Sahelian environment

Rice is the main crop produced in the Senegal River Valley under the semiarid Sahelian climate where water resource management is critical for the resource use sustainability. However, very limited data exit on rice water use and irrigation water requirement in this water scarcity environment under climate change conditions. Understanding crop water requirements is essential for better irrigation practices, scheduling and efficient use of water. The objectives of this study were to estimate crop water use and irrigation water requirement of rice in the Senegal River Valley at Fanaye. Field experiments were conducted during the 2013 hot and dry season and wet season, and 2014 hot and dry season and wet seasons. Three nitrogen fertilizer treatments were applied to rice variety Sahel 108: 60, 120, and 180 kg N ha^?1. Rice water use was estimated by the two-step approach. Results indicated that crop actual evapotranspiration (ETa) varied from 632 to 929 mm with the highest ETa obtained during the hot and dry seasons. Irrigation water requirement varied from 863 to 1198 mm per season. Rice grain yield was function of the growing season and varied from 4.1 to 10.7 tons ha^?1 and increased with nitrogen fertilizer rate. Rice water use efficiency relative to ETa and irrigation requirements increased with nitrogen fertilizer rate while rice nitrogen use efficiency decreased with the nitrogen fertilizer rates. The results of this study can be used as a guideline for rice water use and irrigation water requirement for the irrigation design projects, consultants, universities, producers, and other operators within rice value chain in the Senegal River Valley.     

Evaluation of irrigation water requirements and crop yields with different irrigation schedules for paddy fields in ChiaNan irrigated area,Taiwan

Recent water shortages in reservoirs have caused such problems as insufficient water and fallow rice fields in Southern Taiwan; therefore, comparing irrigation water requirements and crop production of paddy fields using a technique that differs from the conventional flood irrigation method is important. Field experiments for the second paddy field with four irrigation schedules and two repeated treatments were conducted at the HsuehChia Experiment Station, ChiaNan Irrigation Association, Taiwan. Experimental results demonstrate that irrigation water requirements for the comparison method, and 7-, 10- and 15-day irrigation schedules were 1248, 993, 848, and 718 mm, respectively. Compared to the conventional method of flooding fields at a 7-day interval, the 10- and 15-day irrigation schedules reduced water requirements by 14.6 and 27.3 %, respectively; however, crop yields decreased by 7 and 15 %, respectively. Based on the results, it was recommended that the ChaiNan Irrigation Association could adopt 10 days irrigation schedule and plant drought-enduring paddy to save irrigation water requirements for the water resource scarcity in southern Taiwan. The CROPWAT model was utilized to simulate the on-farm water balance with a 10-day irrigation schedule for the second paddy field. A comparison of net irrigation water requirements with the 10-day irrigation schedule from model and field experiment were 818 and 848 mm, respectively, and the error was 3.54 %.     

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.

     

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.     

Climate change’s impact on irrigation system and farmers’ response: a case study of the Plaichumpol Irrigation Project,Phitsanulok Province,Thailand

The Plaichumpol Irrigation Project, in Nan Basin of Thailand, is selected as a case study of impact study, where farmers depended on both surface and groundwater sources (especially in the dry year), to assess the impact on irrigation systems. The study used the MRI-GCM data to project the future climate condition and assess the impact on irrigation systems focusing on water shortage and groundwater pumping aspects in the selected consecutive dry years. The responses from farmers on the impact and adaptation were also gathered via site interviews and analyzed. Based on the bias-corrected MRI-GCM data, the annual rainfall in Nan Basin will decrease in the near future (2015–2039), compared with the past average data (1979–2006), while the rainfall will increase in the far future (2075–2099) compared with past. Water supply from dam will decrease in wet season and dry season, while water demand in both of near future and far future will increase in wet season and dry season. Less water shortage and groundwater pumping in both near-future and far-future periods are expected in the future consecutive dry years compared with the past, though the groundwater is still an important supplementary irrigation water source in the dry year. From the field interview, the farmers are ready to adapt to the changing situations and join in the water use meeting to follow up with irrigation officers about the adjustment of plant calendar and water allocation due to the climate change and to prepare adaptation measures as necessary.     

Climate change’s impact on irrigation system and farmers’ response: a case study of the Plaichumpol Irrigation Project,Phitsanulok Province,Thailand

The Plaichumpol Irrigation Project, in Nan Basin of Thailand, is selected as a case study of impact study, where farmers depended on both surface and groundwater sources (especially in the dry year), to assess the impact on irrigation systems. The study used the MRI-GCM data to project the future climate condition and assess the impact on irrigation systems focusing on water shortage and groundwater pumping aspects in the selected consecutive dry years. The responses from farmers on the impact and adaptation were also gathered via site interviews and analyzed. Based on the bias-corrected MRI-GCM data, the annual rainfall in Nan Basin will decrease in the near future (2015–2039), compared with the past average data (1979–2006), while the rainfall will increase in the far future (2075–2099) compared with past. Water supply from dam will decrease in wet season and dry season, while water demand in both of near future and far future will increase in wet season and dry season. Less water shortage and groundwater pumping in both near-future and far-future periods are expected in the future consecutive dry years compared with the past, though the groundwater is still an important supplementary irrigation water source in the dry year. From the field interview, the farmers are ready to adapt to the changing situations and join in the water use meeting to follow up with irrigation officers about the adjustment of plant calendar and water allocation due to the climate change and to prepare adaptation measures as necessary.

     

Determination of the magnitudes and values for groundwater recharge from Taiwan's paddy field

Flooded paddy fields have many functions, including not only rice production, and ecological and environmental conservation. This work estimates the extent of paddy field infiltration in Taiwan by adopting a one-dimensional Darcy-based soil/water balance model SAWAH (Simulation Algorithm for Water Flow in Aquatic Habitats). A 10 cm thick plow sole layer with a hydraulic conductivity of 0.03 cm/day, coupled with the soil texture and irrigation data obtained from 15 irrigation associations, is used to estimate the volumetric amount of annual infiltration in Taiwan. Simulation results from SAWAH indicate that the plow sole layer controls the movement of infiltrated water, with a rate about 1.8 billion cubic meters annually. The estimated infiltration rate of 1.8 billion m³/yr comprises more than 40% of the annual infiltration recharge to ground water in Taiwan. Additionally, the amount of infiltration recharge to groundwater is equivalent to 20 billion Taiwan dollars NT$ (or 0.65 billion US$) while the yearly rice crop production is 35 billion NT$ (or 1.13 billion US$). It is evident that the infiltration from rice paddy is of great importance to the economy, environment, and water resources conservation in Taiwan.     

Utilizing rainfall and alternate wetting and drying irrigation for high water productivity in irrigated lowland paddy rice in southern Taiwan

Taiwan’s average annual rainfall is high compared to other countries around the world; however, it is considered a country with great demand for water resources. Rainfall along with alternate wetting and drying irrigation is proposed to minimize water demand and maximize water productivity for lowland paddy rice cultivation in southern Taiwan. A field experiment was conducted to determine the most suitable ponded water depth for enhancing water saving in paddy rice irrigation. Different ponded water depths treatments (T_2 cm, T_3 cm, T_4 cm and T_5 cm) were applied weekly from transplanting to early heading using a complete randomized block design with four replications. The highest rainwater productivity (2.07 kg/m³) was achieved in T_5 cm and the lowest in T_2 cm (1.62 kg/m³). The highest total water productivity, (0.75 kg/m³) and irrigation water productivity (1.40 kg/m³) was achieved in T_2 cm. The total amount of water saved in T_4 cm, T_3 cm and T_2 cm was 20, 40, and 60%, respectively. Weekly application of T_4 cm ponded water depth from transplanting to heading produced the lowest yield reduction (1.57%) and grain production loss (0.06 kg) having no significant impact on yield loss compared to T_5 cm. Thus, we assert that the weekly application of T_4 cm along with rainfall produced the best results for reducing lowland paddy rice irrigation water use and matching the required crop water.     

The influence of seepage from canals and paddy fields on the groundwater level of neighboring rotation cropping fields: a case study from the lower Ili River Basin,Kazakhstan

In the large-scale irrigation schemes of the lower Ili River Basin of Kazakhstan, crop rotation combines paddy rice and non-rice crops. Continuous irrigation is practiced in paddy fields, whereas other crops are sustained from groundwater after only limited early irrigation. The water table in non-rice crops is raised by seepage from canals and the flooded paddy fields. We investigated the areal extent to which the groundwater level of non-irrigated fields is influenced by seepage from canals and paddy fields by examining the relationship between distance (from canal and paddy field) and groundwater level in upland fields. The groundwater level was influenced for up to 300 and 400 m from the canals and paddy fields, respectively. Geographic information system analysis of crop and canal patterns in the 11 selected years showed that if the zone of influence is 300 and 400 m from the canals and paddy fields, respectively, the groundwater level of most of the area of upland fields was raised by seepage. We conclude that the water supply to cropping fields by seepage from irrigation canals and paddy fields is adequate, but the spatial distribution of the paddy fields may be an important factor that needs more attention to help improve water use efficiency in this irrigation district.     

Assessment and water saving issues for Ningxia paddies,upper Yellow River Basin

In the Hetao Irrigation Districts of the Ningxia autonomous region, Upper Yellow River Basin, the continuous deep flooding irrigation method is used for the rice paddies. The field irrigation water use during the rice-growing season is two to three times higher than in other regions of North China where water-saving practices have been introduced. This paper, based on the data measured in experimental rice fields and sub-branch canal systems, presents main results concerning crop evapotranspiration, percolation and irrigation requirements for deep and shallow water irrigation. Causes for water waste relate to both the lack of regulation in supply and distribution canals and to the poor management of paddy fields. The potential for water saving is discussed using water balance data. Improved irrigation techniques and water management strategies, including the shallow water irrigation method, are suggested considering the expected impacts and benefits. Replacing the current continuous deep flooding with the shallow-ponded water irrigation method may reduce the growing season irrigation water use from 1,405 to 820 mm in average, with a likely increase in yields of 450 kg/ha. Water productivity would then increase from 0.49 to 1.03 kg/m³. Adopting improved canal management and modernization of regulation and control structures may lead to decreasing the gross irrigation demand from the present 3,100 mm to about 1,280 mm, which would highly benefit the environmental conditions in the area.     

Assessment of the camellia seed meal impact on loaches in paddy fields

In Taiwan, Camellia seed meal is often sprayed on rice paddies during rice transplantation season to stop the growth of Pomacea canaliculata. However, the application of camellia seed meal endangers muciferous mollusks and fishes in paddy fields. Though researchers have examined the effects of the saponin in the camellia seed meal on Pomacea canaliculata, previous studies ignore the effects of saponin on fish. Loaches often inhabit the rivers, lakes, ponds, paddy fields, and canals of low elevation where there have muddy layer with plant chips. This study uses vanillin-sulfuric acid method and field tests on loaches in paddy fields to determine the duration of camellia seed meal’s effect on loaches (Misgurnue Angullicaudatus). Results indicated that the best application to stop the growth of Pomacea canaliculata is to seal the rice field immediately after transplantation, apply the camellia seed meal, and then irrigate the field 2?days after camellia seed meal application for the summer transplantation, and 3?days for the spring transplantation. Water should not be drained from the paddy field after the application of camellia seed meal to reduce the chance of endangering loaches in irrigation canals. Field Tests show that high water temperature during summer also has a negative effect on loaches in paddy fields and irrigation canals.     

稻田高产节水灌溉方式的研究

 1984～1988年在中国水稻研究所实验场排水与其它农业措施相结合，采用节水灌溉措施和高产灌溉制度，综合考虑对田面水、土壤水、地下水和雨水的统一管理利用和合理调节控制，通过大田、小区、测坑试验和生产实践，提出了适合当地条件的节水高产灌排方式、地下水埋深度和排水量。这种水综合运用，既可节约灌溉用水量，减少灌水次数，还可降低排涝水量，减轻排涝能耗费用。     

Performance diagnosis of Mae Lao Irrigation Scheme in Thailand (I) Development of Unsteady Irrigation Water Distribution and Consumption model

The Mae Lao Irrigation Scheme is one of the largest irrigation projects in Northern Thailand. According to the field reconnaissance, water shortage usually occurs during the dry season. And it is very difficult to equally distribute available water to the paddy fields from the upstream to the downstream parts of the system. To understand and identify the causes of the problems, the measurement of water level and flow rate along all canals may be effective. However, it is not easy to achieve this in such a large-scale irrigation system. Thus, the numerical simulation becomes the second option. The objective of this study is to identify and quantify the real water shortage causes by developing an Unsteady Irrigation Water Distribution and Consumption model which can simulate the water movement and consumption in the whole irrigation system. The beneficial area of the right main canal is modeled based on the physical aspect of the system. The components of the model consist of canal networks, control structures, and paddy fields. A canal is divided into several portions called reach. The Saint-Venant equations are applied to describe the unsteady water movement in each reach. Flow movement at the control structure is expressed by the boundary condition. The paddy fields are modeled to make paddy block and connected to each reach. The water consumption in each paddy block is estimated by Paddy Tank model. The numerical model is successfully developed showing the ability to simulate the water movement and consumption properties in this irrigation system.     

Proposal of new return flow analysis by replacement-in-order method for paddy irrigation water

Return flow and repeated use of irrigation water for paddies is the most important issue in the Asian monsoon region, because sometimes this water is applied in greater quantity than that of evapotranspiration plus percolation. A new return flow analysis, the “replacement-in-order method”, which introduces a unique numbering system for very complicated irrigation and drainage networks, is proposed for the main canal with the dual purposes of irrigation and drainage. The method is applied to the Shichika irrigation district in the ordinal (season) irrigation period, resulting in a return flow ratio of 45 % for the entire area. Of this amount, 25 % is available for irrigation again. The remaining 20 % is unavailable, because the return flow discharged directly into a canal lacking a diversion weir in the drainage system, or into the Japan Sea. The return flow ratio is very different at the main canal location, from no return flow to 88 %. With the aid of the above method, theoretical analysis of return flow for paddy irrigation water can be done. This includes the deterministic return flow ratio inside and outside the irrigation area, plus precise information of return flow ratios at various main canal locations and routes of irrigation and drainage water.     

A GIS-based framework of regional irrigation water demand assessment

Although a lot of research has been performed on estimating irrigation water demand at the on-farm level, far less has been done on irrigation water demand for a region-wide basis, such as for a river basin or an area covering multiple river basins. The capture and management of the spatial variations in related data such as soil, climate, crops, and canal networks is the key to effective and efficient regional irrigation water demand estimations. The Geographic Information System (GIS), with its powerful spatial data management and analysis capabilities is used in this study to extend the scope of on-farm irrigation water estimation into a regional estimation. A command area covering several river basins in southern Taiwan was used to build a model prototype. The model framework shows the capability of the system to estimate regional irrigation water demand with most of the spatial variations preserved. The model also shows the capability for quickly reflecting changes in irrigation water demand in response to changes in cropping patterns, a feature that may be a necessary for regional water resource planning.     

Climate Change and Its Repercussions for the Potato Supply Chain

Since the onset of the industrial revolution, in 1750, the concentration of carbon dioxide rose from 290 to 380 parts per million. Especially during the last decennia, the effects of increased greenhouse gases concentrations are being felt. The last 14 years worldwide contained the warmest 13 years since weather recording started. For southern Europe, the major effects reported by the International Panel on Climate Change are reduced water availability and a shorter suitable winter time slot for potato production. For northern Europe, climate change will bring a decreasing number of days with frost and a lengthening of the growing season. It will be associated with more rain in winter and less in summer, with more erratic but heavier rain storms. For potato production in Mediterranean and Sahelian types of climate, during the heat-free period of the year, yields will go down as the suitable period becomes shorter. With a higher evaporative demand, the resource water will be used less efficiently. Potato yields in temperate climates may increase—provided that water for irrigation is available—due to a longer growing season and higher carbon dioxide concentrations in the air. The quality may be affected as larger tubers with a higher dry matter concentration are expected. Problems with pests and diseases are expected to increase with a longer growing season at higher temperature which allows more cycles of multiplication and greater pressure. Late blight will also have a longer period to build up and erratic rains will make control more difficult. Seed production with increased vector pressure will become more costly because fewer field generations will follow the rapid multiplication stage and seed production may move further north. Present potato areas in Europe, however, are more affected by economic factors such as inadequate farm size, changing habits, and remoteness of markets than by climate determined suitability of growing conditions. To remain competitive, the industry will have to invest in strengthening existing production areas and assess the potential of new potato production areas (further north), in new varieties adapted to extremes in weather (heat, drought), in irrigation equipment, in equipment better adapted to wet soil conditions to assure accessibility, and in improved stores with more stores equipped with refrigeration as higher winter temperatures more frequently will make it impossible to keep ware potatoes cool with ambient air. Assessment of both climate change and market liberalization in Europe shows other roads ahead than when only climate effects are taken into consideration.