Paddy Area Research Articles

A refined hydro-environmental watershed model with field-plot-scale resolution

A distributed hydro-environmental model is developed that achieves detailed analysis of the movement of water at a field-plot-scale resolution in a mesoscale watershed including lowland areas where, especially for agricultures, it is an essential need to get rid of redundant groundwater by drainage facilities such as rivers, canals and/or underdrains. For this, the problem geometry is meshed with unstructured cells of triangular shape. Profile of a column cell is zoned into two: surface zone and groundwater zone in which water movement is represented by combined tank and soil moisture sub-models, and well-defined two-dimensional unconfined shallow groundwater flow sub-model, respectively. The top-two sub-models serve to evaluate evapotranspiration, infiltration, soil water content, lateral surface water flow, and vertical percolation. The vertical percolation so evaluated is given as longitudinal recharge to the bottom sub-model for computing groundwater flow. Surface water–groundwater interactions through beds and stream-banks of perennial and ephemeral canals are considered by treating the canal courses as internal boundaries in the groundwater flow model. The finite volume method (FVM) that allows of unstructured mesh and produces conservative solutions is employed for groundwater flow computation. The model developed is applied to an actual watershed which includes a low-lying paddy area to quantify the hydrological impact of land-use management practices over a period of 29 years in which the farmland consolidation project was implemented and part of the paddy fields were converted to upland crop fields and housing lands. From the results obtained, it is concluded that the model presently developed lends itself to water—as well as land-use management practices.

Soil salinity in Aceh after the December 2004 Indian Ocean tsunami

Abstract The 2004 Indian Ocean tsunami inundated about 37,500 ha of coastal farmland in Aceh, and crops planted after the tsunami were severely affected by soil salinity. This paper describes the changes of soil salinity over time on tsunami affected farms and the implications for resuming crop production after natural disasters. Soil salinity and salt leaching processes were assessed across the tsunami affected region by measuring soil apparent electrical conductivity (ECa) using an electromagnetic induction soil conductivity instrument (EM38) combined with limited soil analysis. The ECa was measured 5 times between August 2005 and December 2007 in both the vertical (EMv) and horizontal (EMh) dipole orientations at 23 sites across Aceh. The level of salinity and direction of salt movement were assessed by comparing changes in mean profile ECa and relative changes in EMv and EMh. Eight months after the tsunami the average soil salinity in the 0–1.2 m soil depth varied from ECe 22.6 to 1.6 dS m−1 across sites in the affected region and three years after the tsunami it varied from 13.0 to 1.4 dS m−1. Soil salinity tended to be higher in rice paddy areas that trapped saline tsunami sediments and held seawater for longer periods. Leaching of salts occurred slowly by both vertical displacement and horizontal movement in surface waters. Hence, soil salinity persisted at a level which could reduce crop production for several years after the 2004 tsunami. High soil salinity persisted three years after the tsunami even though there had been more than 3000–7000 mm of accumulated rainfall to leach salts. The slow leaching is likely to have been due to the loss of functional drainage systems and general low relief of the affected areas. Monitoring of soil salinity with EM38 assisted local agricultural extension agencies to identify sites that were too saline for crops and determine when they were suitable for cropping again. The methodology used in this study could be used after similar disasters where coastal agriculture areas become inundated by seawater from storm surges or future tsunamis.

Fundamental Experiments to Develop Eco-Friendly Techniques for Conserving Frog Habitat in Paddy Areas: Escape Countermeasures for Frogs Falling into Agricultural Concrete Canals

Frogs often drown in agricultural canals with deep concrete walls that are installed commonly in paddy areas after land consolidation projects in Japan because they cannot escape after falling into the canal. We propose a partial concrete canal with gently sloped walls as a countermeasure for frogs to escape the canal and investigated the preferable angle of the sloped walls, water depth and flow velocity for Rana porosa porosa. Our experiments showed that only 13 individuals (2%) escaped by leaping out of the canal, indicating that climbing up is the main escape behavior of R. p. porosa. Walls with slopes of 30-45 degrees allowed 50-60% of frogs to escape from experimental canals, the frogs especially easily climbed up walls with a 30 degree slope. Adjusting water depth to 5 cm or more would assist the frogs in reaching the escape countermeasures because at such depths frogs are not able to stand on the canal bottom and to move freely about. Flow velocity should be slower around the countermeasures because R. p. porosa is not good at long-distance swimming and cannot remain under running water for a long time. The broadened inlets of this new canal design provide water of slower velocity near the shores of the sloped walls, which encourages frogs to escape.

Labor Input Allocation for Farmland Conservation in the Hilly and Mountainous Areas

The objective of this paper is to investigate labor requirements for farmland conservation in the hilly and mountainous areas, where aging and depopulation are serious problems. A Random Coefficients Regression (RCR) model with Agricultural Settlements Cards of the Agricultural Census in 2000 is applied to five municipalities in mountainous parts of Hiroshima Prefecture. Each dataset for the model consists of about 100 to 400 agricultural settlement units mainly cropped with rice. Explanatory variables are planted areas of rice paddy categorized into three levels of consolidation condition, beans, vegetables, miscellaneous, and uncropped farmland. The dependent variable is person-days of work on agriculture in each unit. The estimation result supports an observation that farmers are inputting considerable amount of labor although other sampled farm-based statistics, the Statistical Survey on Farm Management and Economy for example, reports further less labor input requirement. Small and unconsolidated rice paddy fields require about 30 to 40 percent more labor input than consolidated ones to be cultivated. Farmers input considerable level of labor even on uncropped farmland. Conversion in monetary value of the labor inputs indicates that current direct payment schemes are not necessarily enough to cover the efficiency gap between small and large field plots. Without direct payments, agricultural income is not sufficient to cover the labor input by farm household members on consolidated rice paddy, and neither to pay out rents both for owned and tenant farmland.

Evaluation of Water Utilization of Farm Pond in Paddy and Upland Irrigation Area

Evaluation of Water Utilization of Farm Pond in Paddy and Upland Irrigation Area

Evaluation of Flood Prevention Function of Paddy Areas and its Utilization on Watershed Management in Future (II)

Evaluation of Flood Prevention Function of Paddy Areas and its Utilization on Watershed Management in Future (II)

Nitrate contamination of groundwater in an agroecosystem in Zhangye Oasis, Northwest China

In order to assess the extent of groundwater contamination by nitrate (NO3 −–N) and to provide information about the deterioration of the groundwater quality in Zhangye Oasis, Northwest China, a study was conducted in this area. The mean value of NO3 −–N concentrations in groundwater samples was 10.66 ± 0.19 mg l−1. NO3 −–N concentrations exceeding 10 mg l−1 (the threshold for drinking water set by the World Health Organization) were found in 32.4% of 71 wells, and were 13, 33.3, 52.4 and 50.0% in the groundwater samples from drinking wells, irrigation wells, hand-pumping wells and groundwater table observation wells, respectively. The result showed that the groundwater samples that had NO3 −–N concentrations exceeding the threshold for drinking water were mostly collected from a depth of less than 20 m. Groundwater NO3 −–N concentrations in areas used for the cultivation of vegetables, seed maize and intercropped maize were significantly higher than those in urban or paddy areas. NO3 −–N contamination of groundwater in areas with sandy soil was more severe than in those with loam soil.

Simulation of Pesticide Behavior in a Paddy Block by a Pesticide Fate and Transport Model

A simulation model (PCPF-B) was developed based on the PCPF-1 model to predict the runoff of pesticides from paddy plots to a drainage canal in a paddy block. The block-scale model now comprises three modules: (1) a module for pesticide application, (2) a module for pesticide behavior in paddy fields, and (3) a module for pesticide concentration in the drainage canal. The PCPF-B model was first evaluated by published data in a single plot and then was applied to predict the concentration of bensulfuron-methyl in one paddy block in the Sakura river basin, Ibaraki, Japan, where a detailed field survey was conducted. The PCPF-B model simulated well the behavior of bensulfuron-methyl in individual paddy plots. It also reflected the runoff pattern of bensulfuron-methyl at the block outlet, although overestimation of bensulfuronmethyl concentrations occurred due to uncertainty in water balance estimation. Application of water management practice such as water-holding period and seepage control also affected the performance of the model. A probabilistic approach may be necessary for a comprehensive risk assessment in large-scale paddy areas.

Risk assessment and validation of flood disaster based on fuzzy mathematics

Floods often take place around rivers and plains, which indicates a higher risk of flooding in these areas. This paper adopts fuzzy comprehensive assessment (FCA), simple fuzzy classification (SFC), and the fuzzy similarity method (FSM) to assess flood disaster risk in Kelantan, Malaysia. Validation data, such as the flooded area, paddy area, urban area, residential area, and refuges, were overlaid to validate and analyze the accuracy of flood disaster risk. The results show that (1) 70–75% of flooded areas lie within the higher and highest risk zones, which shows an effective assessment accuracy; (2) paddy, built-up, and residential areas concentrated in the higher and highest risk zones are more likely to be destroyed by flood disasters; (3) 200–225 refuges in the higher and highest risk zones account for around 50% of all refuges, which means that more refuges should be built in the higher and highest risk zones to meet the accommodation requirement; (4) three methods proved to be feasible and effective in evaluating flood disaster risk, among which FCA is more suitable for the study area than the two other methods.

지역기후모형 자료를 이용한 낙동강 권역의 논 관개용수 수요량 예측

The paddy irrigation demand for Nakdong river basin in Korea due to the climate change have been analyzed using regional climate model outputs. High-resolution (27 <TEX>${\times}$</TEX> 27 km) climate data for SRES A2 scenario produced by the Meteorological Research Institute (METRI), South Korea, and the observed baseline climatology dataset (1971-2000) were used. The outputs from the ECHO-G GCM model were dynamically downscaled using the MM5 regional model by METRI. Maps showing the predicted spatial variations of changes in climate parameters and paddy irrigation requirements have been produced using the geographic information system. The results of this study showed that the average growing season temperature will increase steadily by 1.5 <TEX>$^{\circ}C$</TEX> (2020s A2), 3.2 <TEX>$^{\circ}C$</TEX> (2050s A2) and 5.2 <TEX>$^{\circ}C$</TEX> (2080s A2) from the baseline (1971-2000) 19.8 <TEX>$^{\circ}C$</TEX>. The average growing season rainfall will change by -3.4 % (2020s A2), 0.0 % (2050s A2) and +16.5 % (2080s A2) from the baseline value 886 mm. Assuming paddy area and cropping pattern remain unchanged the average volumetric irrigation demands were predicted to increase by 5.3 % (2020s A2), 8.1 % (2050s A2) and 2.2 % (2080s A2) from the baseline value 1.159 <TEX>${\times}$</TEX> <TEX>$10^6\; m^3$</TEX>. These projections are different from the previous study by Chung (2009) which used a different GCM and downscaling method and projected decreasing irrigation demands. This indicates that one should be careful in interpreting the results of similar studies.

Impact of the December 2004 tsunami on soil, groundwater and vegetation in the Nagapattinam district, India

The tsunami of 26 December 2004 struck the Nagapattinam District, Tamil Nadu, India. Sea water inundation from the tsunami caused salinization problems for soil and groundwater in coastal areas of the district, and also induced salt injuries in crops. To document the recovery of the agricultural environment from the tsunami, we conducted observations of the soil, groundwater, and vegetation. Soil electrical conductivity increased sharply after the tsunami, but returned to pre-tsunami levels the following year. Groundwater salinity returned to pre-tsunami levels by 2006. These rapid rates of recovery were due to the monsoon rainfall leaching salt from the highly permeable soils in the area. MODIS NDVI values measured before and after the tsunami showed that vegetation damaged by the tsunami recovered to its pre-tsunami state by the next rice cropping season, called samba, which starts from August to February. From these results, we conclude that the agricultural environment of the district has now fully recovered from the tsunami. Based on the results, we have also identified important management implications for soil, groundwater, and vegetation as follows: 1) due to the heavy monsoon rainfall and the high permeability of soils in this region, anthropogenic inputs like fertilizers should be applied carefully to minimize pollution, and the use of green manure is recommended; 2) areas that were contaminated by sea water extended up to 1000 m from the sea shore and over pumping of groundwater should be carefully avoided to prevent inducing sea water intrusion; and 3) data from a moderate resolution sensor of 250 m, such as MODIS, can be applied to impact assessment in widespread paddy field areas like the Nagapattinam District.

Pedo-transfer function for saturated hydraulic conductivity of lowland paddy soils

In paddy field, soil saturated hydraulic conductivity (Ks) plays as an important component in the calculation of irrigation requirement of the water balance equation and also for irrigation efficiency. Several laboratory and field methods can be used to determine Ks. Laboratory and field determinations are usually time consuming, expensive and labour intensive. Pedo-transfer functions (PTF) serve to translate the basic information found in the soil survey into a form useful for broader applications through empirical regression of functional relationships, such as simulation modelling. Since PTFs have not been applied to paddy soils in the study area, a lot of field measurements will require high labour input to determine Ks hence high cost. This study attempts to seek a simplified method for determining Ks values based on common existing soil properties through PTF technique. Soil samples (n = 408 samples) were collected randomly depending on the soil series within the 2,300 ha Sawah Sempadan rice cultivation area. Both field work and laboratory work were carried out. The samples were then analysed for the following properties: dry bulk density (Db), soil particle percentage (Sand-S, Silt-Si and Clay-C), organic matter (OM) and geometric mean diameter (GMD). The measured Ks values were obtained by using the falling head method. The parameters were then used as inputs for developing a Ks model by regression analysis using Statistical Analysis System (SAS) package. Stepwise regression analysis was applied to determine the best fit model based on R2 and significant level. The results of the study showed that there is a high spatial variability of the saturated hydraulic conductivity in the paddy area. The best regression model for estimating Ks was based on C, Db, OM and GMD with the dependent variable (Ks) in a form of natural logarithm. The model inputs introduced by stepwise regression are commonly available therefore, this model is useful to replace the conventional method.

Adequacy of Crop Residue Biomass as Renewable Energy Source for Tea Drying in Assam: A Spatial Assessment Debendra Chandra Baruah

Assarn is the largest tea producing state with an annual contribution of about 51% of nation's production. Coal, TD 011, and natural gas are used in tea drying as a source of thermal energy. Crop residue biomass is considered as a potential substitute of fossil energy. Availability of sufficient biomass in the vicinity of user location, avoiding costly transportation, is one of the major considerations. The present investigation makes a spatial analysis of paddy crop residue biomass availability vis-A-vis energy demand in tea drying in ten spatial units representing all the dismcts of Assam. Paddy is a major crop in Assarn and grown in all the districts. Energy availability from paddy crop residue biomass was compared with the thermal energy demand for tea drying. Husk fuelled gasification and straw fired combustion technologies were considered with assumed levels of energy conversion efficiencies. The analysis indicated that tea drying in Assam required 12.43 PJ of thermal energy annually. Total annual available bio-energy was estimated as 5.09 PJ and 23.37 PJ from paddy husk and paddy straw, respectively. Overall, bio-energy availability from paddy husk would be sufficient to fulfil only 40.97% of the demand of the state. However, entire thermal energy demand for tea drying in Goalpara, Kamrup, Lakhimpur, Nagaon and Karbi-Anglong could be fulfilled through husk generated bio-energy in these districts. For the state as a whole as well as in seven spatial units (baring Dibrugarh, Sivasagar and North Cachar), bio-energy available from paddy straw would be adequate to fulfil the thermal energy demand for tea drying. Dibrugarh and Sivasagar were deficient in paddy residue biomass. An index is defined to test the adequacy of crop residue biomass to support energy demand in tea processing as ratio of growing areas of paddy and tea. The districts with ratio more than 3.58 were found to meet the resource adequacy criteria

경기도 벼 재배지 노린재류의 발생소장과 벼 반점미 피해

벼 재배지에서 발생하는 노린재의 종류와 발생소장, 반점미 피해를 구명하기 위해 화성, 평택 등 경기지역 6개 시군 12개 읍면의 논과 논둑에서 노린재 발생밀도와 노린재 종류별 피해양상을 조사하였다. 논둑에서 채집된 노린재는 모두 30종이었고, 화성과 시흥에서 흑다리긴노린재(Paromius exiguus), 평택, 파주, 이천에서 홍색얼룩장님노린재(Stenotus rubrovittatus)가 우점하였다. 논에서 채집된 노린재는 모두 23종이었고, 시흥에서 흑다리긴노린재, 평택, 파주, 이천에서 홍색얼룩장님노린재가 우점하였다. 흑다리긴노린재는 화성 시화호 등 주로 서해안 습지에서 월동하고 증식한 후 이동하여 <TEX>$8{\sim}9$</TEX>월에 논둑에서 최고의 발생을 보였으며, 홍색얼룩장님노린재와 시골가시허리노린재(Cletus punctiger)는 <TEX>$8{\sim}9$</TEX>월에, 가시점둥글노린재(Eysarcoris aeneus)는 <TEX>$6{\sim}7$</TEX>월에 논둑에서 발생이 많았다. 벼에 노린재 종류별로 접종하여 반점미 피해를 확인한 결과, 유숙기 접종시 가시점둥글노린재가 10.2%, 흑다리긴노린재가 4.8%, 호숙기 접종시는 홍색얼룩장님노린재(Stenotus rubrovittatus)가 4.3%, 흑다리긴노린재가 2.7%의 반점미율을 보였다. 흑다리긴노린재에 의한 반점미 피해증상은 피해부위의 표면이 매끈하고 함몰되는 것이 없었으나, 가시점둥글노린재에 의한 반점미 피해증상은 흑다리긴노린재와 유사하지만 피해부위가 함몰되는 것이 많았고 그 표면은 거칠었다. 홍색얼룩장님노린재는 벼 낱알 위쪽을 가해하여 반점이 윗부분에 집중되는 특징이 있었다. This study was carried out to survey the occurrence of stink bugs and pecky rice grain caused by the stink bugs in paddy fields in six districts of Gyeonggi-do. In the levee of the paddy fields, 30 species of the stink bugs were collected, and the dominant species were Paromius exiguus in Hwaseong and Siheung, and Stenotus rubrovittatus in Pyeongtaek, Icheon and Paju. In the paddy fields, 23 species were collected, and the dominant species were Paromius exiguus in Siheung, and Stenotus rubrovittatus in Pyeongtaek, Icheon and Paju. P. exiguus overwintered and proliferated mainly in the west coastal region, where its host plants, Imperata cylindrica and Calamagrostis epigeois, were abundant, and then moved to paddy fields later in the season, resulting in the peak density in September in paddy area. Stenotus rubrovittatus and Cletus punctiger were abundant in paddy area in August and September, and Eysarcoris aeneus was abundant in June and July. When the stink bugs were inoculated on the rice, the rate of pecky rice caused by E. aeneus and P. exiguus at milk ripe stage was 10.2% and 4.8%, respectively, and the rate by S. rubrovittatus and P. exiguus at dough ripe stage was 4.3% and 2.7%, respectively. The damage shape of pecky rice was distinctive according to the species. The surface of pecky rice by P. exiguus was very smooth but the surface of pecky rice by E. aeneus was rough and caved. In the pecky rice by S. rubrovittatus, the spot occurred at the topside of the grain.

Conserving bird species in Japanese farmland: Past achievements and future challenges

A high proportion of threatened and near-threatened species in the world now inhabit farmland. Although much data regarding the impact of agriculture on farmland biodiversity have been accumulated in Western countries, such information, particularly on the impact of rice cultivation, is fragmentary in other parts of the world and has rarely been disseminated internationally. Therefore, this paper aims to clarify what information has become available through earlier studies in Japan, where farmland mainly consists of rice paddy areas, and give directions for future studies about the impact of agriculture on farmland birds in Japan. This study made three notable observations. First, a review of earlier studies of farmland bird species in Japan uncovered some evidence of both increases (e.g., wildfowl and cranes) and declines (e.g., waders) in population size. Second, this paper closely examined case studies of two types of typical farmland birds: (1) geese and cranes foraging on crops and/or harvested remains of crops and (2) waders and egrets foraging on small organisms in farmland, not agricultural crops. This portion of the study identified some potential routes through which human activities in farmland affect bird species in Japan, and offered practical implications for conservation and management of these species supported by scientific data. Finally, based on the results of this review, three key tasks for future conservation studies and practices in Japanese farmland were suggested: (1) establishing quantitative indices based on monitoring surveys in farmland to track the population status, (2) collecting further evidence of the impact of agriculture, particularly on population-level responses by birds, and in a food-web context, and (3) applying evidence-based conservation to practice.

水稲地域における集団的な獣害対策の現状と非農家の協力の可能性―京都府南丹地域の２市町を事例として―

Questionnaire surveys were conducted for all leaders of 209 farmers' unions of Kameoka City and Kyotanba Town in Kyoto Prefecture to analyze the present state of the group activities to decrease agricultural damage caused by wildlife at paddy areas. The group activities in a group were carried out at 70.1% of all farming communities damaged by wildlife, most of which depended on fences for protecting farmlands from wildlife. Of the farming communities, 46.8% answered that they required non-farmers' cooperation for the activities, but it was at only 28.1% of the farming communities where non-farmers cooperated on work or expenses for the activities.

Consideration of Hourly Change in Discharge from a Paddy Area

本稿では，茨城県福岡堰地区を対象に，流出水が集まる中通川（集水面積2,267 ha，うち水田面積1,221 ha）で観測された流量の日内変化に注目し，その原因を検討した．2004年から2006年において，中通川の水位を圧力式自記水位計によって30分毎に連続観測したところ，無降水時には6時頃を最高水位，18時頃を最低水位とする明確な日内変化が確認された．そこで，集水区域内の末端排水路についても水位を連続観測し，また，近隣の水田地帯で観測された蒸発散量記録を入手・検討することで，地域内での水の動きを定量的に分析した．その結果，以下のことが明らかになった．i）本対象地域では，排水路のレベルによらず，水位・流量の変化は同一の傾向を示している．ii）蒸発散量と流量の時間変化はほぼ一致しており，水量的にも高い相関関係が確認された．iii）中通川流量の日内変化は，水田群への安定した用水供給のもと，蒸発散によって水田湛水位が日内変化することによって発生していると推察される．

Agricultural landscape change in China's Yangtze Delta, 1942–2002: A case study

Over the past 60 years, China's ancient agricultural village landscapes have been transformed by unprecedented changes in rural policy, population and agricultural technology. The village landscapes of China's Yangtze Plain are among the most ancient, densely populated and intensively managed in the world and have undergone extremely rapid development in recent decades, causing the wholesale transformation of traditional village landscape structure, primarily at fine spatial scales (< 30 m). Here we investigate the causes and consequences of these fine-scale changes, 1942–2002, using a case study of landscape change within a regionally representative sample of village landscapes in Yixing County. High-resolution mapping was coupled with historical data obtained by interviews with elder farmers and archival sources, with uncertainties quantified using Monte Carlo methods. The already dense agricultural populations of 1942 had increased by about 50% by 2002, and this was accompanied by an intensification of land management that caused 53% of land area to undergo a substantial change in landscape class. Paddy area declined by 22% from 1942 to 2002, and this was coupled with an 8% net increase in built surfaces, a 14% increase in aquaculture surface, and most surprisingly, by a 5% net increase in land cover by closed canopy woody vegetation. Most of this change was caused by fine-scale land transformations that fragmented larger managed features into smaller features that incorporated a wider variety of management practices, thereby simultaneously increasing both landscape heterogeneity and complexity. Population growth, agricultural policy changes and market-oriented land management strategies combined to produce these significant long-term agricultural landscape changes. By coupling detailed analysis of fine-scale local landscape transformation processes with land use history across three time periods, this study identified the causes of ecologically significant landscape changes and may also help to indicate future change trends within some of the most densely populated and productive agricultural landscapes in the world.

Estimating Land Use Impacts on Regional Scale Urban Water Balance and Groundwater Recharge

Anthropogenic activities have exerted increasingly large-scale influences on terrestrial ecological systems from the past century, primarily through agriculture; however, the impact of such changes on the hydrologic cycle is poorly understood. As one of the important land use (LU) in the coastal Dogo Plain of the Seto Inland Sea, Japan, paddy fields have been decreasing with the increase in urbanization in recent decades. As the main source of water in the Dogo Plain, groundwater plays an important role in providing people with fresh water and contributing to stream base flow. The purpose of this study is to analyze the water resource and evaluate the effect of LU change on groundwater table fluctuation in this coastal plain. Firstly, the observations of groundwater table and the investigation of water balance were carried out in this alluvial plain. Then, a distributed four-block three-layer water balance model was employed to analyze the groundwater table fluctuation with response to the change of paddy field area. Moreover, the role of paddy field in recharging groundwater in the basin has been clarified. Results show that groundwater table depends not only on rainfall and discharge from rivers, but also on irrigation water and topology of the study area. The net groundwater recharge was positive in irrigation periods whereas that in non-irrigation periods was nearly equal to zero or negative. The results of this study would be helpful to the urban development policy and land use planning decision.

Use of RADARSAT‐1 data and a digital elevation model to assess flood damage and improve rice production in the lower part of the Chi River Basin, Thailand

In Thailand, flooding due to seasonal monsoon conditions frequently destroys a substantial amount of rice production, the most important agricultural activity of the country. Taking the 2001 monsoon flooding that hit the Lower Chi River Basin as an example, we developed a new method for accurately assessing damage to flood‐affected paddies. A RADARSAT‐1 image acquired during peak flooding was combined with a 30‐m digital elevation model (DEM) to develop a ‘flood‐level‐determination’ algorithm for estimating floodwater depth. Based on the elongation capability of the rice varieties, a water depth of 80 cm was used to separate ‘non‐damaged’ from ‘damaged’ paddy areas, indicating that about 60% of the paddy fields in the flooded areas were non‐damaged paddies. To minimize the loss of rice and maximize farmers' incomes, a map of rice varieties appropriate for the damaged paddy areas was produced, combining the flood‐affected paddy map with the flood frequency map. Our results demonstrate the potential of using single‐date RADARSAT‐1 data and a DEM to provide accurate and economic means of assessing flood damage to rice fields that can be used to improve rice production.