Characteristics of paddy irrigation in Taiwan

Paddy and water environment are closely related to each other in Asia. Developing agriculture by way of construction of farmland irrigation works has long been the principal objective of policies in Taiwan. Owing to significant temporal and spatial difference in rainfalls, natural river runoff has hardly corresponded with irrigation requirements. The cultivation of rice paddies and upland crops are practiced according to the state of the water sources, and cultivation patterns and irrigation systems are framed by placing the same importance on the role of irrigation and drainage management. In this article, the characteristics of paddy irrigation in Taiwan, distinguishable from the western arid farming, have been categorized and will be reviewed in terms of irrigation development, agricultural water utilization, equitable distribution management, farmland consolidation, and the Irrigation Association with its role as that of a public juridical body.Dr. Tsai is the Chief of Irrigation and Engineering Division, Council of Agriculture (COA), Executive Yuan, Taiwan, R.O.C, and also serves as the president of the Chinese Society of Agricultural Engineers (CSAE), the Vice-President of the International Society of Paddy and Water Environment Engineering, the vice-president of International Commission on Irrigation and Drainage (ICID) Chinese Taipei Committee, Managing Supervisor of Chinese Water Resources Management Society. He has an M.Sc. diploma in agricultural engineering from the National Taiwan University and in 1990 he received his Ph.D. degree in natural science and technology from Okayama University, Japan.     

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...     

Prediction of paddy field change based on climate change scenarios using the CLUE model

This study simulated land-cover change using the Conversion of Land Use and its Effects (CLUE) model and predicted future changes in paddy field area under climate change scenarios A1B, A2, B1, and B2 of the Special Report on Emissions Scenarios (SRES). The CLUE model is a dynamic spatial land-use simulation model considering competition among land-use types in relation to socioeconomic and biophysical driving factors. Yongin, Icheon, and Anseong, South Korea, were selected as study areas, and scenarios were developed for regional-level simulation of land-use change. Binary logistic regressions were also conducted to evaluate the relationships between land uses and its driving factors. Finally, the simulation results suggested future changes of paddy field area under the scenario conditions. In all the scenarios, demand for cropland, including paddy and upland, decreased continuously throughout the simulation period of 2000–2100. The decrease in cropland area was particularly steep in scenario A2 in 2050. The receiver operating characteristic (ROC) values indicated that the spatial patterns of land-cover types based on the regressions were reasonably explained by the driving factors. According to the scenarios developed and location characteristics, in scenario A1B, paddy field areas were mainly transformed into built-up areas, while in the other scenarios paddy field areas were mainly transformed into forest. The approach used in this study is expected to enable exploration of future land-use changes under other development constraints and detailed scenarios.     

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.     

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.     

Quantitative risk assessment for reclaimed wastewater irrigation on paddy rice field in Korea

Water shortage has become an important issue for Korean agriculture. Korea suffers from a limited agricultural water supply, and wastewater reuse has been recommended as an alternative solution. This study examined the concentrations of toxic heavy metals and Escherichia coli in a paddy rice field irrigated with reclaimed wastewater to evaluate the risk to farmers. Most epidemiological studies have been based on upland fields, and therefore may not be directly applicable to paddy fields. In this study, a Beta-Poisson model was used to estimate the microbial risk of pathogen ingestion. The risk value increased significantly after irrigation and precipitation. The results of the microbial risk assessment showed that risk values of groundwater and reclaimed wastewater irrigation were lower than the values of effluent directly from wastewater treatment plants. The monitoring results of heavy metals for each irrigated paddy fields did not show specific tendency. A risk assessment for toxic heavy metals was performed according to various exposure pathways; however, the results of the carcinogenic and noncarcinogenic risk estimation showed that the risk from reclaimed wastewater-irrigated paddy fields was the lowest.     

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.     

Numerical simulation on effect of irrigation conditions on water temperature distribution in a paddy field

Water management methods regulate water temperature in paddy fields, which affects rice growth and the environment. To understand the effect of irrigation conditions on water temperature in a paddy field, water temperature distribution under 42 different irrigation models including the use of ICT water management, which enables remote and automatic irrigation, was simulated using a physical model of heat balance. The following results were obtained: (1) Irrigation water temperature had a more significant effect on paddy water temperature close to the inlet. As the distance from the inlet increased, the water temperature converged to an equilibrium, which was determined by meteorological conditions and changes in water depth. (2) Increasing the irrigation rate with higher irrigation water amount increased the extent and magnitude of the effects of the irrigation water temperature. (3) When total irrigation water amount was the same, increasing the irrigation rate decreased the time-averaged temperature gradient effect over time across the paddy field. (4) Irrigation during the lowest and highest paddy water temperatures effectively decreased and increased the equilibrium water temperature, respectively. The results indicate that irrigation management can be used to alter and control water temperature in paddy fields, and showed the potential of ICT water management in enhancing the effect of water management in paddy fields. Our results demonstrated that a numerical simulation using a physical model for water temperature distribution is useful for revealing effective water management techniques under various irrigation methods and meteorological conditions.

     

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.     

Assessing the impact of climate change on the land hydrology in Taiwan

The gradually increased temperature resulting from the enhanced greenhouse effects has been found to be an important factor of changes to the global climate which in turn might significantly affect the Earth's hydrological cycles. The possible outcomes of warming climate are changes of precipitation, surface runoff, evapotranspiration, and frequency of extreme weather events, such as floods and droughts. However, such changes at the global scale may not reflect the variations on a regional scale, and more so at the local scale. In this study, a physically based water balance model was applied to study the impact of climate change on the land hydrology, focusing on trends of surface runoff, evapotranspiration, and infiltration in Taiwan. Model forcing of composite temperatures and precipitations were generated by a weather generation model in association with nine climate change scenarios, including outputs of equilibrium experiments and special reports on emissions scenarios, from the IPCC. Although discrepancies among different climate change scenarios are significant, the trend of more extreme precipitations and surface runoffs were observed in most scenarios' runs. The increase of evapotranspiration in both wet and dry seasons is persistent among different scenarios throughout the island due to the projected consistently higher temperature. Although the trends of infiltration for wet and dry seasons are opposite in curtain scenarios, a decreased yearly infiltration was found in most cases as the result of increased precipitation intensity and more evapotranspiration. Timely adaption measures for water resources managements and natural hazard mitigations are required to face these changes of land hydrology components under changing climate.     

Dissolved nitrogen model for paddy field ponded water during irrigation period

Based on an experimental field study in Japan, a model was developed to simulate dissolved nitrogen in water ponded in a paddy field. As input data, the model uses meteorological data, water balance in the field, nitrogen concentration in inlet water, and the nitrogen contribution of applied fertilizer. Five model parameters need calibration. A practical application of the model is the simulation of NH₄-N and NO₂₊₃-N concentrations in water ponded in a paddy field. The model improves our understanding of the interactions between forms of dissolved nitrogen in ponded water and can explain the complex changes in dissolved nitrogen concentrations in water ponded on a paddy field.     

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 %.     

Modelling of groundwater recharge potential from irrigated paddy field under changing climate

Groundwater recharge from irrigated paddy field under various projected climate change scenarios was assessed using HYDRUS-1D model. Recharge flux, root water uptake, evaporation and surface runoff were simulated on daily time step for the growing period of paddy. Crop evapotranspiration and effective rainfall during the simulation period were estimated to be 301.9 and 269.4 mm, respectively. Cumulative bottom flux, root water uptake, evaporation and surface runoff were 69.2, 23.2, 30.8 and 0.0 cm for sandy loam and 37.2, 23.0, 30.8 and 0.7 cm for clay loam soils, respectively. Simulation results showed that the groundwater recharge potentials in sandy loam and clay loam soils with paddy crop are 69.2 and 37.2 cm, respectively. Cumulative recharge under various climate change scenarios from paddy field varied from 63.9 to 74.4 cm, 33.7 to 39.8 cm, 29.3 to 35.4 cm and 27.1 to 34.3 cm from land units A1 (sandy loam), B1 (clay loam with slight salinity), C1 (clay loam with moderate saline and slight sodic) and D1 (clay loam with strong saline and sodic), respectively. Cumulative recharge flux under the scenarios in which increase in relative humidity along with decrease in duration of sunshine hours was associated with rise in average temperature and wind speed, groundwater recharge would increase by 7.4 %. Cumulative recharge flux under the scenarios which were based on rise in temperature along with the increase in rainfall, groundwater recharge would increase by 0.2–3.9 %. Simulation results also showed that cumulative recharge would decrease under all those scenarios, which were based on rise in temperature only.     

Multifunctionality of paddy fields in Taiwan

Paddy rice is the staple food in Taiwan, where rice farming always plays an important role in agricultural activities. The paddy fields and irrigation activities hold diversified functions, such as production, eco-environmental and living-associated functions. This paper is to provide information regarding the potential magnitude and monetary value of seven functions of paddy fields in Taiwan, including flood mitigation, fostering water resources, preventing soil erosion, purifying water, cooling air temperature, refreshing atmosphere and recreation. For quantification of the above values, replacement cost method (RCM), contingent valuation method (CVM), and the travel cost method (TCM) are adopted. In addition, the ratio of monetary value and their rice production commodity value (R) was also estimated. The results indicated that the flood mitigation function had a monetary value of US$ 389 million each year, and the ratio to the rice production value R was estimated at 37%. Water resource fostering function was US$ 501 million and R at 47%; soil erosion reduction function was US$ 433 million and R at 41%; water quality purification function was US$ 3 million and R at 0.3%; cooling air temperature function was US$ 961 million and R at 91%; refreshing air function was US$ 196 million and R at 19%, health and recreation function was US$ 987 million and R at 93%, respectively. Due to the significant importance of these externalities, it is recommended that the government should properly take into account the multifunctionalities in policy making to ensure sustainable development of agriculture.     

Effect of N-fertilizer application on return flow water quality from a terraced paddy field in Northern Taiwan

Intensive use of chemical fertilizer for crops may be responsible for nitrogen and phosphate accumulation in both groundwater and surface waters. The return flow polluted by nutrients not only results in the limitation of water reuse goals but also creates many environmental problems, including algal blooms and eutrophication in neighboring water bodies, posing potential hazards to human health. This study is to evaluate the N-fertilizer application of terraced paddy fields impacting return flow water quality. Water quality monitoring continued for two crop-periods around subject to different water bodies, including the irrigation water, drainage water at the outlet of experimental terraced paddy field, and shallow groundwater were conducted in an experimental paddy field located at Hsin-chu County, Northern Taiwan. The analyzed results indicate that obviously increasing of ammonium-N (NH₄ ⁺-N) and nitrate-N (NO₃ ^?-N) concentrations in the surface drainage water and ground water just occurred during the stage of basal fertilizer application, and then reduced to relatively low concentrations (<0.1 mg/l and <3 mg/l, respectively) in the remaining period of cultivation. The experimental results demonstrate the potential pollution load of nitrogen can be reduced by proper drainage water control and fertilizer application practices.     

Spatial-uniform application method of methane fermentation digested slurry with irrigation water in the rice paddy field

Promoting biomass utilization, the objectives of this study were to clarify the spatial distribution of nitrogen, one of the most important fertilizer components in the methane fermentation digested slurry (i.e., the digested slurry), and to establish an effective method to apply spatial-uniformly digested slurry with irrigation water in the rice paddy field. A numerical model describing the unsteady two-dimensional flow and solution transport of paddy irrigation water was introduced. The accuracy of this model was verified with a field observation. The tendencies of the TN simulated in inlet and outlet portions had good agreement with the measured data and the accuracy of the numerical model could be verified. Using the numerical model, scenario analyses were conducted to determine the method for spatial-uniform application of the digested slurry with irrigation water. The simulated results indicated that drainage of the surface water and trenches at the soil surface were effective for spatial-uniform application of the digested slurry with irrigation water in the rice paddy fields. The effect of the trenches was maximized when the surface water of the rice paddy field was drained adequately.     

The influence of climate change on irrigation water requirements for corn in the coastal region of Ecuador

This study investigated the irrigation water requirements (IWR) for corn in five provinces of the coastal region of Ecuador that have been influenced by climate change. The weather data were statistically downscaled from six General Circulation Models and compared with the current climate period from 1986 to 2012. CROPWAT 8.0 was used to estimate future IWR for corn cultivation from 2011 to 2100 based on the Representative Concentration Pathways 4.5 and 8.5 scenarios. Also the frequency of predicted rainfall for future periods was analysed to identify the possibility of obtaining the amount of water required for corn plantation from rainfall. The projected trend of future climate showed increases in temperature and rainfall. The predicted IWR showed a decreasing trend in the rainy season and a similar or slightly lower trend in the dry season. Sufficient rain for corn cultivation was predicted for the wet region of the study area, with lower IWR, whereas most of the dry region was shown to have similar patterns of current water demands, except an increase in predicted rainfall resulted in lower IWR in some parts of this region.     

Experimental study on radiation utilization efficiency and soil temperature in paddy field with different irrigation methods in Northeast China

Paddy and Water Environment - In order to investigate the radiation utilization efficiency and soil temperature with different irrigation methods in cold region and black glebe, northeast, China,...     

Increasing water productivity for paddy irrigation in China

This paper introduces the research on practices to increase water productivity for paddy irrigation in China and summarizes the experience on implementation of the alternate wetting and drying (AWD) irrigation technique. The widespread adoption of the AWD practice on 40% of the rice growing area provides an opportunity for China to produce more food in the water-surplus south where it is wet and the traditional based paddy field agriculture is dominant. Physical and institutional measures leading to increasing water and land productivity in rice-based systems are discussed. Research studies show that AWD practice does not reduce rice yield, but does increase the productivity of water. Water use and thus water charges can be reduced. However, experience shows that demonstrations and training are needed to encourage farmer adoption. Furthermore, there are a range of complementary policies and practices, such as volumetric pricing or farm pond development, which provide incentives for adoption of AWD. Finally, there remain many scientific issues to be addressed. Application of the AWD technique in some regions is still very difficult because of both bio-physical and socio-economic problems. In conclusion, the widespread adoption of AWD is only a first step in the continuing effort to find practices that will increase water productivity for paddy irrigation in China.Dr. Yuanhua Li was a Professor and Dean in Wuhan University of Hydraulic and Electric Engineering from 1996 to 2000. After that, he has been a Professor and Deputy Director General of the National Centre for Irrigation and Drainage Development, Ministry of Water Resources, China. He has been doing research on irrigation principally for paddy since 1982.Dr. Randolph Barker is an agricultural economist and Professor Emeritus Cornell University. From 1966 to 1978 he served as head of the Economics Department, International Rice Research Institute, Los Banos, Philippines and from 1995 to 2004 was principal researcher, International Water Management Institute, Colombo, Sri Lanka.