Evaluation of future climate change impact on snow hydrology for a mountainous watershed of South Korea using SLURP model and NOAA AVHRR images

This study is to evaluate the future potential climate impact on snow hydrology using SLURP model for a 6661.0 km² mountainous watershed of South Korea. For the model test, the NOAA AVHRR images were analyzed to prepare snow-related data of the model. Snow cover areas were extracted using channels 1, 3, and 4, and the snow depth was spatially interpolated using snowfall data of 11 ground meteorological stations. With the snowmelt parameters (snow cover area, snow water equivalent, and snow depth), the model was calibrated for 2 sets (2002–2003, 2004–2005), and verified for 2 sets (1997–1998 and 2001–2002) using the calibrated parameters. The average Nash–Sutcliffe efficiencies during the full year period (December to November) and snowmelt period (December to April) were 0.60 and 0.66, respectively. The future climate data of CCCma CGCM2 SRES A2 and B2 scenarios were adjusted and downscaled using change factor method. By the future impact of climate change, the annual dam inflows were projected to change maximum ?29.3 and ?30.4 % for 2090s A2 scenario and 2030s for B2 scenario, respectively. The future dam inflow increased in winter season (December to February) up to 222.0 %, while other periods decreased up to 54.8 %. The future snowmelt increased in December and January by the future temperature increase of 3.9 °C in minimum. The future snowmelt for the 2 months affected the dam inflows during the winter season.     

A combined technique of floodplain storage and reservoir irrigation for paddy rice cultivation

This paper introduces an irrigation system developed in the floodplain of a lake and studies the water management technique of the irrigation system by estimating the total water balance of the whole system. The system is characterized by a reservoir combined with a dike system in the floodplain of the Tonle Sap Great Lake and an irrigation system. Two main models are used for calculating the total water balance. The first model is the water balance of the reservoir. The inputs to the model are water level of the reservoir, precipitation, lake evaporation, infiltration, and area–volume curve of the reservoir. The outputs are inflow and outflow of the reservoir. The supply from the reservoir to paddy fields is computed from the outflow. The second model is the water balance of paddy fields, based on which the water requirement in paddy fields is derived. The reference evapotranspiration needed to calculate the water requirement is simulated for monthly time series using the FAO Penman–Monteith model. Since there is no drainage network in the irrigation system, surface drainage and runoff are not included in the calculation of the water balance, and seepage is considered negligible in the flat floodplain area. The evapotranspiration, rice variety, soil type and irrigated area are used to simulate water consumption in paddy fields. Finally, the two models are connected to produce the total water balance from the reservoir to paddy fields. The total outflow from the reservoir is estimated and the total water consumption for dry season cultivation is also determined. Finally, the efficiency of the whole system is examined.     

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.     

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.     

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.     

Decision support system for reservoir operation considering rotational supply over irrigation blocks

This study aims not only to evaluate agricultural drought in paddy using the storage ratio of the corresponding reservoir, but also to develop a rotational irrigation scheduling system (RISS) for supporting both water supply scheduling and on–off control works for automated irrigation. From the present storage ratio of reservoir and an operation rule curve (ORC) as a guideline for releasing irrigation water, reservoir operators could determine the appropriate time to restrict the irrigation water supply, and calculate the deficient amount of irrigation water. The RISS based on the ORC and weekly rainfall forecasting information has been developed for decision support to minimize drought damage in irrigation districts during the irrigation period. The system was also applied to a test irrigation district with the Yedang irrigation reservoir, which is located in the mid-west of Korea. The RISS could be utilized as a water management program for irrigation reservoirs by interfacing with telemetering and telecontrol (TM/TC) technology.     

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.     

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.     

Nitrogen and phosphorus leaching losses from paddy fields with different water and nitrogen managements

While many water-saving rice production techniques have been adopted in China, the environmental effects of these techniques require further investigation. This study aims to assess nitrogen (N) and phosphorus (P) leaching losses under real conditions in different water and N managements. Two water and three N treatments are conducted in the Taihu Lake region of China. Results show that the total N leaching losses during the rice season under flooding irrigation (FI) are 12.4, 9.31, and 7.17 kg ha⁻¹ for farmers’ fertilization practices (FFP), site-specific N management (SSNM), and controlled-release nitrogen fertilizer management (CRN), respectively. Under controlled irrigation (CI), the respective losses were 7.40, 5.86, and 3.79 kg ha⁻¹ for the same management methods. The total P leaching losses during the rice season under FI were 0.939, 0.927, and 0.353 kg ha⁻¹ for FFP, SSNM, and CRN, respectively. Under CI, the losses were 0.424, 0.433, and 0.279 kg ha⁻¹, respectively, for the same management methods. Ammonium and nitrate N accounted for 42.2–65.5% and 11.8–14.7% of the total nitrogen leaching losses under different water and N management methods, respectively. Due to significant decrease of volumes of percolation water and nitrogen and phosphorus concentrations in percolation water, N and P leaching losses were reduced in the CI treatment compared to the FI treatment under the same N management. The reduction of N input and application of controlled-release nitrogen fertilizer can reduce N and P leaching losses from paddy fields.     

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.     

Effect on water quality in irrigation reservoir due to application reduction of nitrogen fertilizer

Until 1997, tea farmers in the Makinohara district of Shizuoka Prefecture, Japan, applied around 1.2 ton/ha of nitrogen fertilizer per year to their tea fields. In general, uptake amount of nitrogen by tea plants is around 300–350 kg/ha. Then some part of the remainder of nitrogen fertilizer leach into ground water and flow out into the river. The other part of remainder of nitrogen fertilizer is accumulated in the soil layer. Following a recommendation by the local government, this amount was then gradually decreased to 660 kg/ha in 1999 and 540 kg/ha in 2000. Although nitrate nitrogen concentrations in local ground and river water have decreased, they remain high today. The river water runs off from a watershed in the Makinohara area and enters a small irrigation reservoir called Tanno Reservoir, where it has caused deterioration of the water quality, that is, acidification of the reservoir. In Japan, environmental standard for nitrate nitrogen is 10 mg/L in public water body and ground water. Here, the author developed the Water Quality Tank Model, and applied this model to investigate the nitrate nitrogen concentrations in the rivers and an irrigation reservoir called Tanno. The author applies these findings to demonstrate that nitrogen concentrations continue to remain high due to nitrogen accumulation in the soil layer, and that the amount accumulated would be reduced by a reduction in application. The simulation results demonstrate a small decrease in accumulation in the soil layer, and thus that the present high nitrate nitrogen concentrations will continue in ground, river and reservoir water will decrease only gradually.     

Climate Change and Potato Production in Contrasting South African Agro-Ecosystems 2. Assessing Risks and Opportunities of Adaptation Strategies

This study aims to assess the risks and opportunities posed by climate change to potato growers in South Africa and to evaluate adaptation measures in the form of changes in planting time growers could adopt to optimise land and water use efficiencies in potato, using a climate model of past, present-day and future climate over southern Africa and the LINTUL crop growth model. This was done for distinct agro-ecosystems in South Africa: the southern Mediterranean area where potato still is grown year round with a doubling of the number of hot days between 1960 and 2050, the Eastern Free State with summer crops only and Limpopo with currently autumn, winter and spring crops where the number of hot days increases sevenfold and in future the crop will mainly be grown in winter. A benefit here will be a drastic reduction of frost days from 0.9 days per winter to 0. Potato crops in the agro-ecosystems will benefit considerably from increased CO₂ levels such as increased tuber yield and reduced water use by the crop, if planting is shifted to appropriate times of the year. When the crop is grown in hot periods, however, these benefits are counteracted by an increased incidence of heat stress and increased evapotranspiration, leading in some instances to considerably lower yields and water use efficiencies. Therefore year-round total production at the Sandveld stabilizes at around 140 Mg?ha^?1 (yield reduction in summer and yield increase in winter), increases by about 30% in the Free State and stays at about 95 t?ha^?1 at Limpopo where yield increase due to CO₂ is annulled by a shorter growing season. When the crop is grown in a cool period, there is an additional benefit of a reduced incidence of cold stress and a more rapid canopy development in the early stages of crop growth. In all three areas, potato growers are likely to respond to climate change by advancing planting. In Limpopo, a major benefit of climate change is a reduction in the risk of frost damage in winter. The relevance of these findings for potato grown in agro-ecosystems elsewhere in the world is discussed.     

The response of autumn and spring sown sugar beet (Beta vulgaris L.) to irrigation in Southern Italy: Water and radiation use efficiency

The Apulia region in Southern Italy is an important area for sugar beet cultivation. It is characterised by clay soils and a hot-arid and winter-temperate climate. The capability of sugar beet to exploit solar radiation, water use and irrigation supply in root yield, total dry matter and sucrose production was studied and analysed in relation to two experimental factors: sowing date – autumn (October–December) and spring (March) – and irrigation regime – optimal and reduced (respectively with 100 and 60% of actual evapotranspiration). Data sets from three experiments of spring sowing and three of autumn sowing were used to calculate: (1) water use efficiency in the conversion in dry matter (WUE_dm, plant dry matter at harvest versus seasonal water use ratio), in sucrose (WUE_suc, sucrose yield versus seasonal water use ratio); (2) irrigation water use efficiency in the conversion in dry matter (IRRWUE_dm), in sucrose (IRRWUE_suc) and fresh root yield (IRRWUE_fr); and (3) radiation use efficiency (RUE, plant dry matter during the crop cycle and at harvest versus intercepted solar radiation ratio).Autumnal beet was more productive than spring for fresh root, plant total dry matter, sucrose yield and concentration; also WUE_suc and IRRWUE_s were higher in the autumnal sugar beet, but no difference was observed in WUE_dm (on average, 2.83 g of dry matter kg⁻¹ of water used). An average saving of about 26% of seasonal irrigation supply (equivalent to about 100 mm) was measured in the three years with the earliest sowing time. The optimal irrigation regime produced higher root yield, plant total dry matter and sucrose yield than the reduced one; on the contrary the IRRWUE_fr and IRRWUE_dm were higher in the reduced irrigation strategy. WUE_s and IRRUWE_s correlated positively with the length of crop cycle, expressed in growth degree days and, in particular, to the length of the period from full soil cover canopy to crop harvest, the period when plant photosynthetic activity and sucrose accumulation are at maximum rates. Seasonal RUE was higher in the spring than in the autumn sowing (1.14 μg J⁻¹ versus 1.00 μg J⁻¹). The RUE values during the crop cycle reached the maximum in the period around complete canopy soil cover. The results showed the importance for better use of water and radiation resources of autumnal sowing time and of reduced irrigation regime in sugar beet cropped in a Mediterranean environment.     

Wise use of paddy rice fields to partially compensate for the loss of natural wetlands

This paper reviews the scientific information related to climate change impacts on wetlands and functions of human-made wetlands such as paddy rice field and treatment wetland are described to partially compensate for the loss of natural wetlands. Wetlands are among the world’s most productive environments and are cradles of biological diversity, providing the water and primary productivity upon which countless species of plants and animals depend for survival. Considerable evidence suggests that some global warming is occurring, which has important implications for wetland system as well as human life and wildlife. Direct effects of climate change on wetlands are likely to be accentuated by human induced changes that will increase stress to wetland ecosystems. The Ramsar Classification System for Wetland Type provides three broad categories: marine/coastal wetlands, inland wetlands, and human-made wetlands. Human-made wetlands are as important as natural wetlands, and the largest human-made wetland is a paddy rice field (130,000,000 ha) taking about 18% of total global wetland, which is second only to natural fresh wetlands. Paddy rice fields provide not only rice production for food, but also diverse multi-functionalities such as flood control, groundwater recharge, soil erosion control, water quality purification, air purification and cooling, wildlife habitat, amenity and social benefits. The economic value of multi-functionalities estimated by contingent valuation method (CVM) and travel cost method was in the range of U$ 9.75–11.46 billion, which is greater than the value of rice production itself in Korea. Unfortunately, there is an indication of decreased area in paddy rice field in Korea after 1990 showing about 20% decrease in 15 years. Another human-made wetland type is a constructed wetland for water purification, and thousands hectares of wetlands are scheduled to be constructed for reservoir water quality improvement in next 5 years in Korea, and their application is expected to be more common in near future. There is a growing consensus that wetlands are critically important ecosystems that provide globally significant social, economic and environmental benefits. Wise use of human-made wetlands is as important as conservation of natural wetlands, which can be a viable element to overall climate change mitigation and can partially compensate for the loss of natural wetlands.     

Evaluation of water intake rate using the diffusive tank model in the low-lying paddy area

The subject of this study is water management in low-lying paddy fields. The objective of this study is to quantify the water requirement, and estimate an appropriate volume and facilitate management of irrigation water in areas where it is difficult to estimate the flow rate continuously. A field observation was conducted at a 14-ha study site located in the Kuwabara area, Fukuoka City, southwest of Japan, to evaluate water management conditions in the command area of the reservoir. This site near the reservoir was selected, because it was impossible to understand the water supply situation in the entire command area. The farmers in this region have been unable to retain sufficient irrigation water. The observation results indicate that the water depth fluctuates widely in every irrigation canal. The canals are frequently empty because rotational irrigation is conducted by water managers; this makes quantifying the flow rate in the irrigation canal very difficult. To quantify the water requirement, an improved tank model was introduced. The accuracy of the model was examined by comparing the observed and calculated ponding depths at a paddy field. The simulation results agreed with the observed data. Using this model, water management for the reduction of water managers’ labor was simulated. Simulation results indicated that rotational irrigation effectively reduces labor and saves irrigation water.     

The role of paddy rice in recharging urban groundwater in the Shira River Basin

Agricultural fields in the middle Shira River basin play an important role as a source of groundwater recharge; however, the water balance between the agricultural water and river water is unclear. This study was conducted to investigate the water balance in the fields by measuring the stream flow of agricultural water channels, which draw water from the Shira River. The flow rate of water channels was found to increase in the beginning of May, which corresponded to the cultivation of paddy rice fields. During summer, the total agricultural intake was comparable to the river flow observed in the middle Shira River Basin. Determination of the water budget for the targeted area revealed that most of the recharged water was dependent on agricultural irrigation from the river. The annual recharge of the overall target area was estimated to be as high as 15,300 mm. In addition, the infiltration rate was as high as 170 mm/day in the paddy fields during summer, and as high as 30 mm/day in the upland fields during winter. In order to recover the groundwater recharge in this region, it is necessary to extend the submerged period to include periods in which the stream water in the Shira River is not subject to heavy rainfall as well.     

SWAT modeling of best management practices for Chungju dam watershed in South Korea under future climate change scenarios

Suitable and practicable best management practices (BMPs) need to be developed due to steadily increasing agricultural land development, intensified fertilization practices, and increased soil erosion and pollutant loads from cultivated areas. The soil and water assessment tool model was used to evaluate the present and future proper BMP scenarios for Chungju dam watershed (6,642 km²) of South Korea, which includes rice paddy and upland crop areas. The present (1981–2010) and future (2040s and 2080s) BMPs of streambank stabilization, building recharge structures, conservation tillage, and terrace and contour farming were examined individually in terms of reducing nonpoint source pollution loads by applying MIROC3.2 HiRes A1B and B1 scenarios. Streambank stabilization achieved the highest reductions in sediment and T-N, and slope terracing was a highly effective BMP for sediment and T-P removal in both present and future climate conditions.     

Numerical assessments of the impacts of climate change on regional groundwater systems in a paddy-dominated alluvial fan

Quantitative assessment of the impacts of climate change on groundwater levels is important for sustainable groundwater use. This study examined the Tedori River alluvial fan in Ishikawa Prefecture, Japan, where paddy fields occupy 45 % of the total area. A regional groundwater flow model simulated future groundwater levels in response to 38 climate change projections generated for each of three GCMs, using three GHG emission scenarios with the ELPIS-JP datasets. The numerical groundwater flow model consisted of a 1-D unsaturated water flow model (HYDRUS-1D) for estimating groundwater recharge and a 3-D groundwater flow model (MODFLOW). Variable parameters consisted of daily air temperature, precipitation, humidity, solar radiation, and wind speed, which influence groundwater through infiltration, evapotranspiration, snowfall, and snowmelt. Groundwater levels had both decreasing and increasing trends, depending on climate change. There were more decreasing than increasing trends, and the maximum groundwater drawdown during 2010–2090 was ~1 m. Groundwater level was most sensitive to change in rate of precipitation during the non-irrigation period. Variations of relatively low-intensity precipitation days, when daily precipitation was <10 mm, had an effect on groundwater level. These results contribute to development of adaptive and sustainable groundwater managements (e.g. land use management and pumping strategies) in the future.     

稻鱼综合种养有害藻类生态防控技术

稻田养殖中,田块长期覆水,晒田时间较少,特别是夏季高温天气,由于养殖渔类,水体营养丰富,容易发生藻害,降质减产.介绍了稻田养殖中几种主要有害藻类(蓝藻、水绵、刚毛藻、水网藻)产生的原因与危害,并结合水稻(一季稻)生长时期从四个季节简述了有效防控有害藻类的技术.