Effect Of Rainfall Research Articles

The catastrophic 13 November 2015 rock-debris slide in Lidong, south-western Zhejiang (China): a landslide triggered by a combination of antecedent rainfall and triggering rainfall

ABSTRACTOn 13 November 2015, a disastrous rockslide-debris avalanche occurred in the Lidong village of Liandou District, Lishui City (south-western Zhejiang, China), which overwhelmed 27 houses and killed 38 people in the village. The geological survey on the slope revealed that prior to this incident, a rupture zone existed between the highly weathered volcanic rock and the underlying weathered volcanic rock in this slope. The rupture zone has dip direction coinciding with the slope aspect and some of the existing cracks in the surface are likely extended from the surface to the rupture zone. This study summarizes the past history and main characteristics of the landslide, simulates the correlation between the safety factor of the slope and the rainfall level using a physically based triggering model, and analyses the distribution of the effective antecedent rainfall that influences landslide occurrence, showing that the landslide on 13 November 2015 was triggered by the very low intraday rainfall and the 15-day antecedent rainfall. The results demonstrate that for a potential unstable slope with increasingly wet antecedent conditions, very low daily rainfall may be able to trigger landslides on a given day, which is important for improving landslide warning systems based on the rainfall–landslide relationship.

Assessing the Potential of Rain-Water Harvesting (in situ) for Sustainable Olive (Olea europaea L.) Cultivation in Water-Scarce Rain-Fed Areas

The improvement of water productivity in olive cultivation and its production on sustainable basis in areas marked as water deficit. The most essential, natural and cheapest water resource in such water-prone areas of the world is rainfall. The collection and constructive use of rain-water runoff, also known as water harvesting, has the potential to cope with the water scarcity in the semi-arid and dry, sub-humid regions of the world to sustain olive production. Among all the available micro-irrigation techniques, construction of micro catchments can help farmers to produce crops such as olive orchards with minimum water resources. Research experiments were conducted at Barani Agricultural Research Institute (BARI), Pakistan situated in region where the climate is semi-arid subtropical and the annual rainfall varies from 500-1000 mm. To compare water productivity of different micro-catchment methods, three field plots with three different shapes i.e., square, rectangular, and triangular (V shape) were constructed with 3-5% slope. Olive trees, due to their expensive premium quality edible oil and natural adaptability to grow in marginal lands and better drought tolerance, were used as subject crop to evaluate the performance of micro catchments rain water harvesting techniques. Results concluded that micro catchment structures showed significantly better yield (8-9%) as compared to control and are best suitable to sloppy terrene. Only three supplement irrigations were required for sustainable olive plant cultivation through drip/bubbler irrigation system. Average effective rainfall of both years was 594 mm from which 505 mm (85%) was used by olive plants in micro catchments. Conclusively, micro-catchment structure can be utilized as efficient technique to harvest rain water and sustainable cultivation of olive in semi-arid and arid climates.

CHOICE OF THE DESIGN RAINFALL FOR SEWERAGE ASSESSMENT USING ANALYTICAL TOOL DATER IN SLOVAKIA

Storm water management in urbanized areas is currently a global issue. In order to verify the correct functioning of the sewer networks and their objects, it is necessary to regularly assess their hydraulic capacity. Key of assessing the capacity of single and rainwater sewer networks is the calculation of the amount of surface runoff and the selection of a suitable design rainfall model. This article deals with the issue of effective decision making in the choice of the design rainfall for the hydraulic assessment of the sewer systems. DATER (decisive analytical tool for effective rainfall) was used as a analytical tool for rain analysis. This article incorporates case study in town of Vráble. During this research, several meteorological stations have been allocated in the area of interest in order to record actual rainfall data leading to its comparison with synthetic design rainfall.

How can streamflow and climate-landscape data be used to estimate baseflow mean response time?

Mean response time (MRT) is a metric describing the propagation of catchment hydraulic behavior that reflects both hydro-climatic conditions and catchment characteristics. To provide a comprehensive understanding of catchment response over a longer-time scale for hydraulic processes, the MRT function for baseflow generation was derived using an instantaneous unit hydrograph (IUH) model that describes the subsurface response to effective rainfall inputs. IUH parameters were estimated based on the “match test” between the autocorrelation function (ACFs) derived from the filtered base flow time series and from the IUH parameters, under the GLUE framework. Regionalization of MRT was conducted using estimates and hydroclimate-landscape indices in 22 sub-basins of the Jinghe River Basin (JRB) in the Loess Plateau of northwest China. Results indicate there is strong equifinality in determination of the best parameter sets but the median values of the MRT estimates are relatively stable in the acceptable range of the parameters. MRTs vary markedly over the studied sub-basins, ranging from tens of days to more than a year. Climate, topography and geomorphology were identified as three first-order controls on recharge-baseflow response processes. Human activities involving the cultivation of permanent crops may elongate the baseflow MRT and hence increase the dynamic storage. Cross validation suggests the model can be used to estimate MRTs in ungauged catchments in similar regions of throughout the Loess Plateau. The proposed method provides a systematic approach for MRT estimation and regionalization in terms of hydroclimate and catchment characteristics, which is helpful in the sustainable water resources utilization and ecological protection in the Loess Plateau.

Water pricing following rainfall distribution and its implications for irrigation agriculture: A case study from Vélez Blanco, Andalusia (1967–2006)

This study uses data from water auctions, conducted by the traditional irrigation community of Vélez Blanco. Water prices are comprehensively compared and statically correlated with local precipitation data on different temporal scales; the data analyzed reach back to 1967. The local prevailing Mediterranean climate is characterized by a mean annual precipitation amount of 419mm, while effective rainfall (≥1mm) occurs averagely at 37days per year. The rainfall distribution data used were of daily, seasonal and annual resolution and are assessed on their influence on the local water price formation. The results were validated with information about local agricultural practices and subjective perceptions of the vega’s status, gained from interviews with local farmers. Results show that high correlation coefficients are achieved when water prices and precipitation data are correlated on a monthly scale. The highest correlation coefficients are achieved with a temporal offset of one month throughout the spring and summer season. Interestingly, neither short term water surplus, nor long term water deficit (consecutive drought years) are clearly reflected. Based on the given data-base, annual rainfall distribution has proven to be a significant factor that influences water price formation in the Vega of Vélez Blanco.

An analysis of the unit hydrograph peaking factor: A case study in Goose Creek Watershed, Virginia

Study regionGoose Creek Watershed, Loudoun County, Virginia, USA. Study focusExisting U.S. Army Corps of Engineers (USACE) policy suggests that the unit hydrograph peaking factor (UHPF) – taken as the unit hydrograph peak of any flood runoff, including the probable maximum flood, over unit hydrograph peak of the inflow design flood (IDF) – range between 1.25 and 1.50 to ensure dam safety. It is pertinent to investigate the impact of extreme flood events on the validity of this range through physically based rainfall-runoff models not available during the planning and design of most USACE dams. The UHPF range was analyzed by deploying the Gridded Surface Subsurface Hydrologic Analysis (GSSHA) model. New hydrological insightsThis study concludes that design events with return periods greater than 5-years are required for the UHPF to fall within the guidance range and that UHPF becomes less sensitive to rainfall intensity with increasing accumulation time. An effective rainfall factor (ERF) is introduced to validate existing UHPF guidance as well as provide a nonlinear UHPF scaling relation when effective rainfall does not match that of the UH design event. Finally, a method for quantifying the effect of hydrologic parameter and precipitation magnitude uncertainty on UHPF are demonstrated. The Goose Creek facility is shown to maintain dam safety given current UHPF guidance as it was designed using 25-year return-period rainfall.

Quantifying Roughness Coefficient Uncertainty in Urban Flooding Simulations through a Simplified Methodology

A methodology is presented which can be used in the evaluation of parametric uncertainty in urban flooding simulation. Due to the fact that such simulations are time consuming, the following methodology is proposed: (a) simplification of the description of the physical process; (b) derivation of a training data set; (c) development of a data-driven surrogate model; (d) use of a forward uncertainty propagation scheme. The simplification comprises the following steps: (a) unit hydrograph derivation using a 2D hydrodynamic model; (b) calculation of the losses in order to determine the effective rainfall depth; (c) flood event simulation using the principle of the proportionality and superposition. The above methodology was implemented in an urban catchment located in the city of Athens, Greece. The model used for the first step of the simplification was FLOW-R2D, whereas the well-known SWMM software (US Environmental Protection Agency, Washington, DC, USA) was used for the second step of the simplification. For the training data set derivation, an ensemble of 100 Unit Hydrographs was derived with the FLOW-R2D model. The parameters which were modified in order to produce this ensemble were the Manning coefficients in the two friction zones (residential and urban open space areas). The surrogate model used to replicate the unit hydrograph derivation, using the Manning coefficients as an input, was based on the Polynomial Chaos Expansion technique. It was found that, although the uncertainties in the derived results have to be taken into account, the proposed methodology can be a fast and efficient way to cope with dynamic flood simulation in an urban catchment.

What Do They Have in Common? Drivers of Streamflow Spatial Correlation and Prediction of Flow Regimes in Ungauged Locations

AbstractThe spatial correlation of daily streamflows represents a statistical index encapsulating the similarity between hydrographs at two arbitrary catchment outlets. In this work, a process‐based analytical framework is utilized to investigate the hydrological drivers of streamflow spatial correlation through an extensive application to 78 pairs of stream gauges belonging to 13 unregulated catchments in the eastern United States. The analysis provides insight on how the observed heterogeneity of the physical processes that control flow dynamics ultimately affect streamflow correlation and spatial patterns of flow regimes. Despite the variability of recession properties across the study catchments, the impact of heterogeneous drainage rates on the streamflow spatial correlation is overwhelmed by the spatial variability of frequency and intensity of effective rainfall events. Overall, model performances are satisfactory, with root mean square errors between modeled and observed streamflow spatial correlation below 10% in most cases. We also propose a method for estimating streamflow correlation in the absence of discharge data, which proves useful to predict streamflow regimes in ungauged areas. The method consists in setting a minimum threshold on the modeled flow correlation to individuate hydrologically similar sites. Catchment outlets that are most correlated ( ) are found to be characterized by analogous streamflow distributions across a broad range of flow regimes.

The effects of stemflow on redistributing precipitation and infiltration around shrubs

Abstract The experiments of stemflow of two semiarid shrubs (Caragana korshinskii and Hippophae rhamnoides) and its effect on soil water enhancement were conducted from 1st May to 30th September of 2009-2013 in the Chinese Loess Plateau. Stemflow values in C. korshinskii and H. rhamnoides averaged 6.7% and 2.4% of total rainfall. The rainfall threshold for stemflow generation was 0.5 and 2.5 mm for C. korshinskii and H. rhamnoides. When rainfall was less than 17.0 mm, the funnelling ratios were highly variable, however, stable funnelling ratios were found for rainfall greater than 17.0 mm for C. korshinskii. The funnelling ratios of H. rhamnoides first increased until a threshold value of 10.0 mm and then the funnelling ratios begin stabilize. The wetting front depths in the area around stem was 1.4-6.7 and 1.3-2.9 times deeper than area outside the canopy for C. korshinskii and H. rhamnoides. Soil moisture at soil depth 0-200 cm was 25.6% and 23.4% higher in soil around stem than that outside canopy for C. korshinskii and H. rhamnoides. The wetting front advanced to depths of 120 and 100 cm in the area around stem and to depths of 50 cm in the area outside the canopy for C. korshinskii and H. rhamnoides suggested that more rain water can be conserved into the deep soil layers through shrub stemflow. Soil moisture was enhanced in the area outside the shrub canopy, only when rainfall depth is > 4.7 and 5.1 mm, which is an effective rainfall for the area for C. korshinskii and H. rhamnoides. While for the area around stem of C. korshinskii and H. rhamnoides, the corresponding threshold values are 3.2 and 4.3 mm. These results confirmed that stemflow has a positive effect on soil moisture balance of the root zone and the enhancement in soil moisture of deeper soil layers.

An estimation of water resources in flooded, connected underground mines

When studying discharges in closed mines with relevant environmental impact, the first step is to undertake a complete hydrogeological study of the mining system. In this study, some inactive and flooded coal mines in NW Spain were characterized. The water resources (recharge) of each mine were evaluated considering the infiltration of effective rainfall over mined areas, the groundwater contribution, and the losses from surface watercourses. The studied mine drainage corresponds to a mining reservoir of 5 connected mines. The resources of this reservoir were estimated in 54L s−1 for an average year, coming mainly from rainfall as well as losses from irrigation systems during the summer. The volume of voids of the reservoir was estimated by using different approaches: the calculation of the void left by the mining activity and the volume of infiltrated water during the mine flooding. In this particular case, the volume of voids below the discharge level (water reserves) are estimated to be around 1Mm3, which makes them useful for storage and regulation of water, as well as for the production of energy. The acid mine water discharge is of poor quality, and affects the receiving watercourses. Strategies, such as the reduction of the mine's water flow, avoiding water level fluctuations, and passive treatment systems could be applied to diminish these negative effects. The methodology explained here is believed to be suitable for application in closed mines where there is not much information available.

Determination of patterns of rainfall history creating situations for accurate classification of rain-fed paddy fields with SAR backscatter coefficients

It is worthwhile to classify paddy fields based on the long-term frequency of ponding, which strongly determines the yield of rice. However, the direct measurement of the frequency requires a large number of backscatter images from synthetic aperture radar (SAR). Another approach is the indirect estimation of the relative frequency of ponding from differences in ponding frequency with the same rainfall history. Any combination of backscatter coefficients with such rainfall history should result in a high accuracy of classification of paddy fields based on the relative frequency of ponding. This study aims to establish methodologies for the classification of rain-fed paddy fields into two categories: ‘wet’ and ‘dry’ fields, based on ponding frequency using a small number of time-series SAR backscatter coefficients that depend on the flood situation and soil water content of the land surface. By analyzing 21 images acquired by the ALOS-PALSAR during 2007–2011, patterns of rainfall history with obvious large differences between the two categories of paddy fields were determined. Through supervised classifications using a random forest classifier, it was evident that the backscatter coefficients onset of rainy seasons for years with an above average precipitation, would be suitable as variables for accurate classification. In years where the precipitation (1379mm/year) neared the average (1330mm/year), the supplementary use of a quartile deviation of the backscatter coefficient within each plot, that indicated a degree of partial ponding, increased the classification accuracy. It was also evident that the effective rainfall index, which registers a rough estimate of rainwater acculturation in the soil, was useful in the determination of periods of significantly large variations in the backscatter coefficient between categories of rice fields.

Water Footprint as an Emerging Environmental Tool for Assessing Sustainable Water Use of the Bioethanol Distillery at Metahara Sugarcane Farm, Oromiya Region, Ethiopia

In Ethiopia, sugarcane estate farms and bioethanol distilleries are being expanded at an alarming rate to provide alternative sustainable energy as renewable, affordable, and low carbon footprint bioenergy for the transportation sector. The promotion of bioethanol production is definitely poised to cause high competition for water resources. Thus, the aim of this study was to investigate the water footprint (WF) of sugarcane molasses-based bioethanol production of the Metahara sugarcane farm. Ten years of meteorological data (2007–2016) were collected from the Metahara weather stations and processed through the CROPWAT 8 model using the Penman-Monteith method. Sugarcane coefficient (K c ) was taken from FAO data; and sugarcane growing seasons, fertilizer application rates, sugarcane yield, and factory data were obtained from the Metahara factories. Reference evapotranspiration varied from 4.73 to 7.98 mm/day whereas effective rainfall (R eff) values ranged from 256.4 to 743.6 mm/growing season of sugarcane (16 months). The estimated sugarcane water requirement (SWR) ranged from 2544.1 to 4833.3 mm/growing season. The ANOVA test (p > 0.05) for R eff showed statistically insignificant differences in means but the test for SWR (p < 0.05) revealed a statistically significant differences in means. The average sugarcane WF was 217.69 m3/t whereas the bioethanol WF was 3106.7 L/L. Hence, the WF of bioethanol production in the Metahara distillery is higher than the global average, indicating pressure on local water resources. Therefore, the results of this study may help policy makers to develop appropriate water resource management for the extensively growing sugar and bioethanol industries in Ethiopia.

Estimation of Evapotranspiration andIrrigation Scheduling of Lentilusing CROPWAT 8.0 Model for Anantapur District, Andhra Pradesh, India

To achieve effective water allocation and planning, the information about Lentil crop water requirements, irrigation withdrawals, soil types and climate conditions were gathered from the study area i.e. Anantapur district of Andhra Pradesh (A.P). The main objectives of the study area wereto estimate the Lentil crop water requirement (i.e., evapotranspiration) and deciding the proper sowing time in semi-arid agro-climatic conditions.The CROPWAT 8.0 was used to estimate the climatic water deficit, net irrigation requirement (NIR) and gross irrigation requirement (GIR) under different rainfed and irrigated conditions with six different growing dates with aninterval of 10 days.The results showed that the best sowing dates were last week of September to 1st week of October, which gives thebest utilization of rainfall as effective rainfall. The net and gross irrigation requirement(NIR and GIR) varied from a minimum to maximum as 69.7 mm, 110.3 mm, 78.2 mm, 119.4 mm, 114 mm and 165.9 mm; respectively for all sowing dates. Thus by adopting a proper sowing date and irrigation scheduling criteria, it is possible to save 49.7 mm of water as NIR for theearly sown crop.

CONSUMPTIVE USE OF WATER BY SELECTED CASH CROPS IN MALAYSIA

A rapid development in economic sectors has induced the water depletion in most of the developing country, particularly for Malaysia. This study estimates the consumptive water use of cultivating 5 cash crops, i.e. cassava, maize, rice, sugarcane and sweet potato in Peninsular Malaysia. The consumptive water uses for cultivating these 5 crops was determined based on the CROPWAT 8.0 and Penman Monteith model. CROPWAT 8.0 model was used to compute the evapotranspiration and crop water requirement (effective rainfall and irrigation requirement) of the cash crops grown in Peninsular Malaysia from 2005-2013 (9 years). It was found that the green water uses for cultivating cassava, maize, paddy, sugarcane and sweet potato for Peninsular Malaysia is higher than the blue water use. In conclusion, water use for cultivating agricultural crops will accelerate the competition on the consumption of clean water with the other sectors. However, the availability of water resource in Peninsular Malaysia is sufficient to fulfil the demands for water at the present time.

An inexact stochastic-fuzzy optimization model for agricultural water allocation and land resources utilization management under considering effective rainfall

Agricultural water management faces challenges from ecological environment stress (e.g. water scarcity issues, land resources pressure, and climate conditions) and uncertainties exist among multifarious activities in agricultural water resources management systems. In this study, an inexact stochastic-fuzzy programming model was proposed for irrigation water resources allocation and land resources utilization management under considering multiple uncertainties. In the model, uncertainties can be directly integrated into the optimization process through reflecting parameters and coefficients as interval values, fuzzy sets, random variables, and their combinations. The developed method is applied to planning irrigation water resources allocation and cropland pattern under considering the limited surface water and groundwater, the random effective rainfall, and the imprecise crops water requirements in Jining City. A number of scenarios corresponding to different fuzzy probability of violating constraint are examined in order to obtain the best management program under various scenarios, and search reasonable tradeoffs between varied system benefit and system-failure risk. The results indicated that agricultural water allocation is explicitly affected by uncertainties expressed as randomness and fuzziness, and the results are valuable for supporting the adjustment or justification of the existing water resources management schemes and a desired land utilization plan for regions socioeconomic development under uncertainty.

Hydrologic behavior of model slopes with synthetic water repellent soils

In the natural environment, soil water repellency decreases infiltration, increases runoff, and increases erosion in slopes. In the built environment, soil water repellency offers the opportunity to develop granular materials with controllable wettability for slope stabilization. In this paper, the influence of soil water repellency on the hydrological response of slopes is investigated. Twenty-four flume tests were carried out in model slopes under artificial rainfall; soils with various wettability levels were tested, including wettable (Contact Angle, CA<90°), subcritical water repellent (CA∼90°) and water repellent (CA>90°). Various rainfall intensities (30mm/h and 70mm/h), slope angles (20° and 40°) and relative compactions (70% and 90%) were applied to model the response of natural and man-made slopes to rainfall. To quantitatively assess the hydrological response, a number of measurements were made: runoff rate, effective rainfall rate, time to ponding, time to steady state, runoff acceleration, total water storage and wetting front rate. Overall, an increase in soil water repellency reduces infiltration and shortens the time for runoff generation, with the effects amplified for high rainfall intensity. Comparatively, the slope angle and relative compaction had only a minor contribution to the slope hydrology. The subcritical water repellent soils sustained infiltration for longer than both the wettable and water repellent soils, which presents an added advantage if they are to be used in the built environment as barriers. This study revealed substantial impacts of man-made or synthetically induced soil water repellency on the hydrological behavior of model slopes in controlled conditions. The results shed light on our understanding of hydrological processes in environments where the occurrence of natural soil water repellency is likely, such as slopes subjected to wildfires and in agricultural and forested slopes.

Standardization of alternate wetting and drying (AWD) method of water management in low land rice (Oryza sativa (L.))

Alternate wettting and drying (AWD) systems save water compared with continuoussubmergence (CS) irrigation. However, the reported effect on yield varies widely and detailedcharacterizations of the hydrological conditions of AWD experiments are often lacking so thatgeneralizations are difficult to make. We compared the effects of AWD and CS on crop andwater productivity in rice in the field experimentations in India. The experiment was conductedin irrigated lowlands and followed AWD practices by using field water tube. Crop and waterproductivity was significantly differed between AWD and CS of irrigation. The average grainyield was 5.8–7.4 t ha-1 with AWD irrigation methods and 7.5–7.6 t ha-1 with CS. The pooledvalues of irrigation water applied, effective rainfall and seasonal volume of water input variedfrom 1390, 216 and 1646 mm, respectively under CS and 708 to 1142 mm, 238 to 300 mm and1048 to 1420 mm, respectively under AWD irrigation regimes. Irrigation water applied in AWDirrigation regimes amounted to 50.9 to 82.1% of CS (1390 mm), averaged over two seasons, thecrop in different AWD irrigation regimes used water 63.6 to 86.2% of the CS (1646 mm)suggesting that the AWD practice enabled water saving of 13.8 to 36.4% in different treatments.Therefore, in view of considerable water saving (26.6 to 35.0%) and higher water productivitythe AWD method of water management is the best practice to meet the cope of water scarcity inlowland rice production.

Reference evapotranspiration (ETo) and irrigation water requirement of different crops in Bihar

For irrigation scheduling and better management of the water, estimation of irrigation water requirement of the crop is essentially required. The study was conducted for estimation of daily reference evapotranspiration (ETo) by FAO Penman-Monteith method using 30 years (1985-2015) mean meteorological data of two locations Sabour (zone III A) and Patna (zone III B) in Bihar. The crop evapotranspiration was estimated using crop coefficients of different crops like rice,kharif maize, wheat, rabi maize, green gram and summer maize at Sabour and Patna locations. Irrigation water requirement for different crops was estimated based on crop evapotranspiration and effective rainfall during the growing period of the crop. The mean annual reference evapotranspiration (ETo) was found 3.6 mmday-1 at Sabour and 4.1 mmday-1 at Patna. The total crop evapotranspiration was maximum for rice crop in kharif season 546.0 and 607.3 mm at Sabour and Patna respectively and lowest for wheat crop in rabi season 212.9 mm and 243.3 mm at Sabour and Patna respectively. Net irrigation water requirement was maximum for summer maize366.3at Sabour and 508.2 mm at Patna for rice crop whereas lowest in kharif maize 67.5 and 161.4 mm at Sabour and Patna respectively.

Spatiotemporal Patterns of Crop Irrigation Water Requirements in the Heihe River Basin, China

Agricultural expansion, population growth, rapid urbanization, and climate change have all significantly impacted global water supply and demand and have led to a number of negative consequences including ecological degradation and decreases in biodiversity, especially in arid and semi-arid areas. The agricultural sector consumes the most water globally; crop irrigation alone uses up more than 80% of available agricultural water. Thus, to maintain sustainable development of the global economy and ecosystems, it is crucial to effectively manage crop irrigation water. We focus on the arid and semi-arid Heihe River Basin (HRB), China, as a case study in this paper, extracting spatiotemporal information on the distribution of crop planting using multi-temporal Thematic Mapper and Enhanced Thematic Mapper Plus (TM/ETM+) remote sensing (RS) images. We estimate the spatiotemporal crop irrigation water requirements (IWRc) using the Food and Agriculture Organization of the United Nations (FAO) Penman-Monteith method and reveal variations in IWRc. We also analyze the impact of changes in crop planting structure on IWRc and discuss strategies for the rational allocation of irrigation water as well as policies to alleviate imbalance between water supply and demand. The results of this study show that effective rainfall (ER) decreases upstream-to-downstream within the HRB, while crop evapotranspiration under standard conditions (ETc) increases, leading to increasing spatial variation in IWRc from zero up to 150 mm and between 300 and 450 mm. Data show that between 2007 and 2012, annual mean ER decreased from 139.49 to 106.29 mm, while annual mean ETc increased from 483.87 to 500.38 mm, and annual mean IWRc increased from 339.95 to 370.11 mm. Data show that monthly mean IWRc initially increased before decreasing in concert with crop growth. The largest values for this index were recorded during the month of June; results show that IWRc for May and June decreased by 8.14 and 11.67 mm, respectively, while values for July increased by 5.75 mm between 2007 and 2012. These variations have helped to ease the temporal imbalance between water supply and demand. Mean IWRc values for oilseed rape, corn, barley, and other crops all increased over the study period, from 208.43, 349.35, 229.26, and 352.85 mm, respectively, in 2007, to 241.81, 393.10, 251.17, and 378.86 mm, respectively, in 2012. At the same time, the mean IWRc of wheat decreased from 281.53 mm in 2007 to 266.69 mm in 2012. Mainly because of changes in planting structure, the total IWRc for the HRB in 2012 reached 2692.58 × 106 m3, an increase of 332.16 × 106 m3 (14.07%) compared to 2007. Data show that 23.11% (76.77 × 106 m3) of this increase is due to crop transfers, while the remaining 76.89% (255.39 × 106 m3) is the result of the rapid expansion of cultivated land. Thus, to maintain both the sustainable development and ecological security of the HRB, it is crucial to efficiently manage and utilize agricultural water in light of spatiotemporal patterns in IWRc changes as well as IWRc variations between different crops. The cultivation of water-demanding crops and the further expansion of agricultural land should also be avoided.

GCM‐related uncertainty in forecasting irrigation and design water requirement for paddy rice fields

ABSTRACTThe aim of this study is to identify the global circulation model (GCM)‐related uncertainties regarding the climate‐change impacts that affect the water management in paddy rice fields. The crop evapotranspiration, effective rainfall, net irrigation water requirement (NIWR), and design water requirement (DWR) were simulated from 1981 to 2100 using 36 climate‐change outputs of 23 GCMs. In particular, the DWR indicates the NIWR of a drought with a 10‐year return period, which is used for the design of an agricultural reservoir in the Republic of Korea. The NIWR is the main factor for determining irrigation water supply and managing agricultural water resource. The average changes of the NIWR compared with the periods from 1981 to 2014 are from 5.2 to 8.3% in the central region and from 3.2 to 6.1% in the southern region under RCP (representative concentration pathways) 4.5. The largest increase from the average NIWR was simulated by the MIROC‐ESM (745.8 mm year−1). These results showed that the selection of GCM could lead to overestimates or underestimates of the potential impacts of climate change. Therefore, water managers should consider that each GCM simulated a different NIWR to enable the application of the appropriate GCMs for drought management, water‐resource development, or irrigation supply. Under the GCMS variations, an NIWR was identified, thereby allowing for a DWR estimation for which multi‐GCMs were used. Under RCP 4.5, the DWR gradually increased in future periods compared with the trends from 1981 to 2014, and the average rates increased 9.4% and 6.0% in the central and southern regions, respectively. The results showed that if the capacity of an agricultural water‐resource facility is maintained at its present status, an increase of the DWR may lead to water‐supply shortage.