Total Crop Water Requirement Research Articles

Crop water requirement and irrigation scheduling under climate change scenario, and optimal cropland allocation in lower kulfo catchment

Crop water requirement and irrigation scheduling in Lower Kulfo Catchment of southern Ethiopia have not assessed under climate change scenarios, and the allocation of crop land also not optimal that signifcantly challenges to crop productivity.Therefore, this study was conducted to evaluate the effects of climate change on future crop water requirements, and irrigation scheduling, and to allocate cropland optimally. Bias of projected precipitation and temperature were corrected by utilizing Climate Model data with the hydrologic modeling tool (CMhyd). Alongside, crop water requirements and irrigation scheduling were assessed using Crop Water Assessment Tool. After estimating crop water requirement, crop land were allocated optimally using General Algebraic Modeling System programming with non-negativity constraints (scenario 1), and non-negativity constraints based on farmers adaptation (scenario 2). Average reference evapotranspiration from 2030 to 2050 and 2060 to 2080 was increased by 11.9 %, and 16.2 %, respectively compared with the reference period (2010–2022). The total seasonal crop water requirements were 4,529 mm, 4866.7 mm, and 5272.2 mm under 2010 to 2022, 2030 to 2050, and 2060 to 2080 climate change scenarios, respectively. The meean irrigation interval in 2010–2022, 2030 to 2050, and 2060 to 2080 climate change scenarios were 8 days, 7 days, and 5 days, respectively. This irrigation interval was decreased by 14 % (2030–2050), and 34 % (2060–2080) compared with the reference period. In 2030 to 2050 and 2026 to 2080 climate change scenarios, the required irrigation water at the inlet of main canal increased by 6.8 %, and 18 %, respectively. The optimal allocated area for tomato (60.4 %), maize (20.8 %), and watermelon (18.8 %) in scenario 1 with net benefit of 1.47*108 Ethiopian Birr. The allocated areas in scenario 2 were (48 %) for maize, (31.6 %) for tomato, and (20.4 %) for watermelon with 1.34*108 Ethiopian Birr net benefit it was reduced by 19.1 % compared with the net benefit in scenario 1. Fruit crops alone may not suffice for local food needs and to address this, small farmers should grow maize, tomato, and watermelon. This research aids policymakers in encouraging climate-resilient agriculture and improving small-scale farmers' awareness through conducting workshops and training.

Estimation of irrigation water requirement and irrigation scheduling for major crops using the CROPWAT model and climatic data

Abstract The world is facing an acute water shortage. The present irrigation techniques used in the Hyderabad district, Pakistan, are not demand-driven. The present study was carried out to determine the crop water requirement (CWR), irrigation water requirement (IWR), and irrigation scheduling for major crops grown in the Hyderabad district using the CROPWAT model based on climatic, soil, and crop data. The analysis revealed that the total CWR for the entire growing season for sugarcane, banana, cotton, and wheat were 3,127.0; 2,012.3; 1,073.5; and 418.9 mm, respectively. However, the IWR for sugarcane, banana, cotton, and wheat for the entire growing season was found to be 2,964.0; 1,966.7; 1,052.7; and 407.6 mm, respectively. However, the contribution of rainfall was 163.0, 45.6, 20.8, and 11.3 mm during sugarcane, banana, cotton, and wheat, respectively. The CWR and IWR were higher during the dry season due to high temperatures and low relative humidity. However, the IWR of each crop was low in the initial stage which increased with the growing stage until the peak at the full growth stage. The study recommends the use of CROPWAT to investigate the irrigation water requirements with accuracy.

Estimation of Crop Water Requirements and Irrigation Scheduling for Major Crops Grown in India's North-Eastern Region

The water demand of some agricultural crops grown in Assam was assessed in this research. To estimate the crop water requirements of potato, chili, and brinjal, the FAO-CROPWAT model was used. The climatic parameters like rainfall, solar radiation, wind speed, sun hours, relative humidity, minimum and maximum temperature were collected for 30 years from the Indian Meteorological Department (IMD) to estimate the crop water requirement (CWR). The reference evapotranspiration (ETo) was computed by using the Food and Agriculture Organization (FAO)-recommended Penman-Monteith method and was found to vary from 1.84 mm/day to 4.49 mm/day. The calculated ETo was further used to compute the CWR, the net irrigation requirement (NIR), and the gross irrigation requirement (GIR) to plan for irrigation application during the growing stages of the selected crops. The total CWR of potato, chili, and brinjal was estimated to be 260.6 mm, 262.1 mm, and 274.2 mm, respectively, and the total NIR of potato, chili, and brinjal sowed on the 1st of October was found to be 162.8 mm, 149.0 mm, and 167.2 mm, respectively, with an irrigation efficiency of 70%. In December, the CWR and NIR of potato and brinjal were found to be the highest. The month with the least effective rainfall (8.5 mm) was December. The findings of the study showed that efficient irrigation water management and irrigation scheduling can be achieved by using the CROPWAT model to maximize crop yield and minimize crop water stress.

Relieving water stress by optimizing crop structure is a practicable approach in arid transboundary rivers of Central Asia

With the challenges of arid transboundary river water management among Central Asian countries, it is important to evaluate the water stress and propose practicable climate adaptation strategies. This study used the Syr Darya Basin (SDB) in a Central Asia data scarce region as the study area and, conducted the first quantified analysis of the spatiotemporal characteristics of water supply and requirements at the basin and irrigation district scale; identified its driving mechanisms based on systematic monitoring data concerning reservoir regulation and complex crop structure from 2000 to 2018; and a climate change scenario combined with a crop restructuring scenario was applied to evaluate water conservation effects and propose a climate adaptation strategy from 2019 to 2030. The results showed that runoff increased by 7.45 billion m3 but the water withdrawal decreased by 3.42 billion m3 after reservoir regulation in the basin during 2000–2018. Due to the unified water allocation, it was challenging to conduct and usually exceeded the plan by 0.4–8.5 %. The total crop water requirement (TCWR) mainly derived from cotton (61.5 %), winter wheat (12.1 %) and rice (13.9 %) increased by 3.15 billion m3 (+30.7 %) and the influence of crop area (380 million m3/a) was greater than that of climate (130 million m3/a). The wind speed (27.5 %) and rice area (19.2 %) also significantly contributed to the TCWR variation. The contradiction between water supply and requirement resulted in water scarcity in the basin. From 2019–2030, the water conservation effect of winter wheat (+20 %) under the restructuring scenarios reached 28.7 mm, which helped relieve water stress under the scenario of a 0.51–0.91 °C increase. Thus, priority planting of a winter wheat rotation and low water consuming crops is a practicable approach for coping with water scarcity and adapting to climate change in arid transboundary rivers of Centra Asia.

An Artificial Intelligence Approach to Manage Crop Water Requirements in South Africa

Estimation of crop water requirements is of paramount importance towards the management of agricultural water resources, which is a major mitigating strategy against the effects of climate change on food security. South Africa water shortage poses a threat on agricultural efficiency. Since irrigation uses about 60% of the fresh water available, it therefore becomes important to optimise the use of irrigation water in order to maximize crop yield at the farm level in order to avoid wastage. In this study, combined application of an artificial neural network (ANN) and a crop – growth simulation model for the estimation of crop irrigation water requirements and the irrigation scheduling of potatoes at Winterton irrigation scheme, South Africa was investigated. The crop-water demand from planting to harvest date, when to irrigate, the optimum stage in the drying cycle when to apply water and the amount of irrigation water to be applied per time, were estimated in this study. Five feed –forward backward propagation artificial neural network predictive models were developed with varied number of neurons and hidden layers and evaluated. The optimal ANN model, which has 5 inputs, 5 neurons, 1 hidden layer and 1 output was used to predict monthly reference evapotranspiration (ETo) in the Winterton area. The optimal ANN model produced a root-mean-square error (RMSE) of 0.67, Pearson correlation coefficient (r) of 0.97 and coefficient of determination (R2) of 0.94. The validation of the model between the measured and predicted ETo shows a r value of 0.9048. The predicted ETo was one of the input variables into a crop growth simulation model, called CROPWAT. The results indicated that the total crop water requirement was 1259.2 mm/decade and net irrigation water requirement was 1276.9 mm/decade, spread over a 5-day irrigation time during the entire 140 days of cropping season for potatoes. A combination of the artificial neural networks and the crop growth simulation models have proved to be a robust technique for estimating crop irrigation water requirements in the face of limited or no daily meteorological datasets.

Assessment of Sectoral Virtual Water Flows and Future Water Requirement in Agriculture Under SSP-RCP Scenarios: Reflections for Water Resources Management in Zhangye City

Water scarcity is a core issue that constraints the high-quality development of arid areas in northwestern China. Zhangye is an oasis city located in the Heihe River Basin in northwestern China. It is populated with an agriculture-dominated economy and faces more and more serious water crises. Virtual water is an indicator that can measure the embodied water in the traded products, which has been widely applied for making rational policies for water resources management. In addition, clarifying water requirements in agricultural sectors under future climate change scenarios is essential to develop more appropriate adaptation strategies. From this perspective, this study aims to evaluate and compare virtual water flows among various sectors in Zhangye for the years 2012 and 2017 with a single regional input-output model and to further clarify the future water requirement tendency in agriculture during 2020–2050 under different shared socioeconomic pathways and representative concentration pathways (SSP-RCP) scenarios. The results showed that the planting sector directly contributed most of the total water consumption with the highest direct coefficient of 3307.5 m3/yuan in 2012, whereas the manufacture of food products and tobacco processing sector had the largest proportion of indirect water consumption (99%) mainly from intermediate inputs of agricultural products. Water consumption intensity of all sectors on average decreased by 22% during 2012–2017, indicating an increasing water utilization efficiency in economic industries. Household consumption also can improve water utilization efficiency as the major pathway for final consumption (86.4% in 2017). Water scarcity in Zhangye was becoming increasingly prominent since virtual water net exports were higher than local consumption, especially in the agriculture, manufacturing, and energy supply industries. Moreover, under climate change scenarios, we found the highest level of water requirement per unit area occurred in 2000, but it still had an incremental potential by 2050, especially in SSP585. The high requirement intensity and large-scale maize planting caused a rising tendency of total crop water requirement with an annual increasing rate of 8.4% from 1980 to 2050. This makes it possible to adapt to climate change through scientific management measures and technical means. We further made policy implications for adaptive management of water resources in Zhangye.

Quantifying Impacts of Future Climate on the Crop Water Requirement, Growth Period, and Drought on the Agricultural Watershed, in Ethiopia

Quantifying the influence of climate change on the crop growth period, water requirement, and drought conditions is essential for integrated crop production system planning. In this study, the effects of climate models from the Coupled Model Inter-comparison Product (CMIP5) on Crop Water Requirement (CWR), Length of Growth Period (LGP), and drought conditions were quantified for Lake Hawassa watershed in Ethiopia. In this study, two regional climate models were selected that showed better performance on the evaluation criteria after applying a quantile mapping bias correction procedure. The impact analysis was conducted for two Representative Concentration Pathways (RCPs) (RCP4.5 and RCP 8.5). Drought analysis was performed using the standardized anomalies of rainfall (S-index). The future growing season of the area is projected to be between April 15 and May 1 on average for all years. The total crop water requirement was projected to increase to a value of 3,258.7 mm on average under both the RCP4.5 and RCP8.5 scenarios for all the stages at the end of 2080s from its baseline value of 3,180.4 mm. In addition, the drought forecast analysis shows extreme drought with S-index values <−1.6 in the 2050s and 2080s under RCP 8.5. Of all the time periods, the 2050s recorded the smallest number of years (10 out of 30 years) with a positive S-index value, indicating projected precipitation shortages during these time periods under RCP 8.5. With this result, the combined impacts of climate change on crop production factors are expected to be high in the region. The results suggest an early warning for the study region considering low economic and technological development as in many developing parts of the world. Therefore, understanding the future changes in climate variables and their impacts can be an important input for developing a better plan for adaptation and mitigation measures.

Estimation of Crop Water Requirement Based on Planting Structure Extraction from Multi-Temporal MODIS EVI

Estimation of crop water requirement (CWR) is key to the rational water use and agricultural water conservation in arid regions. Using remote sensing data to obtain long-term CWR over large areas helps water resources management in water-scarce areas. This study, taking the Kaidu-Kongqi River basin in arid northwest China as the study area, investigated the feasibility of synergistically using phenological characteristics, Savitzky-Golay filter, harmonic analysis and decision tree to extract crop planting structures (CPS) from MODIS EVI, and meanwhile analyzed the spatiotemporal variation in the estimated CWR. The results show that the integrated method for CPS identification and extraction is feasible and reliable with the classification accuracy over 80%. The mid-season stage requires the most water and cash crops need more water than cereal crops. Summer accounts for 69% the total growing season water use. The significant increase in the area of high water demand crops such as cotton raised the total CWR of the basin surging from 14.91× 108m3 in 2000 to 34.92×108m3 in 2017. The spatial distribution of CWR was more related to crop types and area than to climatic conditions. Controlling the expansion of arable land and optimizing the agricultural planting structure remain important tasks for the sustainable management of water resources in the basin.

Application of FAO-CROPWAT Modelling on Estimation of Irrigation Scheduling for Paddy Cultivation in Batticaloa District, Sri Lanka

Agriculture sector is one of the main sources of income in the North eastern and some of the North western parts of Sri Lanka. Over the past decade, many countries around the world have witnessed a growing scarcity and competition for water among different users. Since Agriculture is the major user of water, improving agricultural water management is essential to any irrigation management approach specially to apply the exact amount of water to the field in order to meet crop water requirement. This study aims to estimate water requirement of rice by using the model CROPWAT. According to the study, effective rainfall was found to be 601mm and 133 mm in Maha and Yala season respectively. Total crop water requirements are 349 mm and 436 mm in Maha and Yala season respectively. Irrigation scheduling carried out by CROPWAT revealed that, the gross irrigation requirement is 473 mm and net irrigation requirement is 331 mm. Net scheme irrigation requirements are 40, 106, 100 and 22 mm per month in May, June, July and August respectively. Further, flow of net scheme irrigation requirements is found to be 0.15, 0.41, 0.37 and 0.08 l/s/ha in May, June, July and August respectively. Therefore, the model for planning of irrigation water requirements of rice is very important for efficient utilization of water and to meet the possible change of climate in agricultural sector.

Evaluation of water demand and supply under varying meteorological conditions in Eastern India and mitigation strategies for sustainable agricultural production

Spatio-temporal variability of water demand and supplies under different meteorological conditions and their linkage with dynamic groundwater (annually utilizable groundwater) reserve was investigated in a Canal Command (area irrigated by a canal system) of Eastern India. Annual irrigation water supply from surface water sources (i.e., canal, river lift and tanks) and groundwater sources (i.e., shallow and deep tubewells) was estimated for different meteorological conditions. Annual water demands as crop irrigation requirements (CIRs) for the prevailing cropping patterns in the study area were also assessed under different meteorological conditions using crop evapotranspiration and effective rainfall data. Thereafter, the estimated irrigation water supply and irrigation water demand were subjected to spatio-temporal and statistical analyses. The mean annual CIR in the study area was estimated at 7002 ± 852 MCM during 2004–2013 period. Boro paddy was found to be the most water-consuming crop, accounting for about 50% of the total crop water requirements. The mean annual dynamic groundwater reserve (DGWR) in the study area was estimated to be 5169 ± 782 MCM. Considering DGWR as an additional source of irrigation water, 28, 25 and 35 blocks were characterized as ‘water surplus’ during ‘normal,’ ‘dry’ and ‘wet’ years, respectively. Also, DGWR substantially reduced demand–supply gaps in the remaining blocks. The surplus water available in the blocks due to DGWR availability could be used to mitigate water-deficit condition in neighboring blocks. Thus, this study suggests cost-effective alternatives for the efficient management of available water resources and identifies management strategies for sustainable agricultural production under diverse climatic conditions.

Increased crop water requirements have exacerbated water stress in the arid transboundary rivers of Central Asia

Water scarcity and ecological degradation as a result of the expansion of irrigated agriculture in arid regions have become global issues. A better understanding of the changes in crop water requirements (CWRs) is important for promoting sustainable development, particularly the water resource management of transboundary rivers. In this study, the latest and complete meteorological station and crop area data, the CropWat model, and the slope method were used to estimate the CWR in the Syr Darya Basin (SDB) of Central Asia from 2000 to 2018. The spatiotemporal variation of the water requirements for primary crops at the city scale was first assessed. The impacts of climate and cultivated land change on the CWR were quantified, and the associated impacts of the CWR on the water resources and environment were discussed. The results revealed that the mean unit area CWR of the SDB was 944.1 mm and the rate of increase was 7.6 mm/a from 2000 to 2018. The area of the primary crops expanded by 5851.6 km2, and the total CWR increased at a mean rate of 2.0 × 108 m3/a, with the majority of this change being concentrated between 2010 and 2018. By 2018, the total CWR reached 194.8 × 108 m3. The lower reaches of the SDB were associated with a high CWR and a high rate of increase. Along with the reduction in basin water resources, the increased CWR has exacerbated the water stress in the SDB. Sensitivity analysis indicated that the dominant factors influencing the change in the CWR are cultivated land change (65.0%) and climate change (35.0%). Owing to a reasonable crop planting structure, the middle reaches maintained a relatively low CWR and rate of increase. Given the predicted changes in climate, optimizing crop planting structure and controlling the expansion of cultivated land in order to reduce the CWR can help to mitigate water scarcity.

Analysis of climate change effects on crop water availability for paddy, wheat and berseem

Climate change has been a serious concern in the 21st century and mitigation strategies on its effects are less researched. The increase in temperature and changes in rainfall have forced researchers to ponder over reducing the wastage of fresh water. This paper deals with the rain water availability and the crop evapotranspiration (ETc) changes occurring and projected to occur over a time period of fifty years. Three major crops, paddy, wheat and berseem fodder were considered for three locations. Observed data and forecasted data for precipitation and temperature was obtained from India Meteorological Department and Can Esm2 model respectively. The Mann–Kendall (MK) test and the Thiel-Sen's Slope estimator (TSS) test were applied on the crop stage wise aggregated rain water available and the ETc to analyze the effects of climate change. In addition to the above study, the historical and projected means of crop period wise aggregated effective rainfall, total net irrigation requirement and total crop water requirement for a range of dates of sowing/transplanting for the above mentioned crops and locations were analyzed. It was seen by the analysis that the rainwater availability is seen to decrease and the temperatures increase with a delay in the sowing dates in the future scenarios causing an increase in the crop water requirements. Suitable shifting of the crop sowing or transplanting dates is seen to aid to better exploit the available rainwater and minimize the irrigation application.

Water Budgeting of Babhulgaon Micro Watershed under Deficit Rainfall Years

Water budget under deficit rainfall years was conducted at Babhulgaon micro watershed, Parbhani district of Maharashtra state considering crop water demand, human and livestock consumption. On the main streams, there were nala bunds and farm ponds constructed for rainwater harvesting and supplemental/protective irrigation. During the year 2014, a total rainfall of 398.1 mm was received, which was 52% deficit than average normal rainfall. The major losses were occurred as soil evaporation and transpiration are 59.71 mm and 155.26 mm, respectively. The surface runoff of 29.87 mm (11%) was estimated and the soil moisture of 103.50 mm was utilized for crop growth and which was found to be insufficient for normal crop growth, thus effected the crop yields. The crop water requirements of kharif and rabi season were 339.45 and 70.10 ha-m, respectively. The total crop water requirement of the year 2014 was 409.55 ham. During 2015, an amount of 407.8 mm of rainfall received which was 51% deficit to average normal monsoon rainfall. The major losses observed were due to soil evaporation and transpiration as 61.94 mm and 161.61 mm respectively. In 2015, rainfall was well distributed and only two storms were observed in the month of September resulted in a surface runoff of 18 mm which was 4.42% of rainfall. The ground water recharge contribution was 52.36 mm (12.84% of rainfall). The soil moisture storage of 107.77 mm was observed and found to be insufficient for crop growth. The crop water requirement of kharif and rabi season was 337.55 and 81.00 ha-mm, respectively. The total crop water requirement of the year 2015 was 418.55 hamm. The outflow characteristics indicated that there is additional possibility for construction of rainwater harvesting structures like nala bunds, earthen dams and farm ponds etc., because total available water storage capacity in all existing structures is about 21 to 35% of annual runoff only. The deficiency of water resources in the Babhulgaon micro watershed can be managed by harvesting the available potential runoff and its efficient utilization through modified cropping pattern.

Assessing the Effect of Different Water Table Depths on Water Use, Yield and Water Productivity of the Okra Crop

An experimental study was carried out on a Lysimeter with the aim of partially meeting WRs (Water Requirements) of the Okra crop through SWT (Shallow Water Table) while maintaining the SWT at various levels below the ground surface. Under the study, CWR (Crop Water Requirement), yield, water productivity, salt accrual and contribution of SWTs towards meeting the CWR are assessed. The study was designed in accordance with the principles of CRD (Complete Randomized Design) with three treatments and four replications. The treatments; viz. T 1 , T 2 , and T 3 consisted of maintaining the WTDs (Water Table Depths) at 45, 60 and 75 cm, respectively, below the ground surface. The crop was irrigated with a good quality water having EC w = 0.50 dS m-1 and pH = 7.3. The results of the study showed that the crop consumed the maximum amount of water under T 1 treatment, followed by T 2 and then by T 3 treatment. Accordingly, the contribution of SWTs towards the CWR is 94.8, 93.2 and 42.9% of the total CWR under the T 1 , T 2 , and T 3 treatments, respectively. Maximum yield is attained under T 3 treatment, followed by T 2 treatment and then by T 1 treatment. Likewise, maximum water productivity is achieved under T 3 treatment, followed by T 2 treatment and then by T 1 treatment. The dry bulk density (ρ ρ ρ ρ ρ d) of the soil, under T 1 and T 2 treatments, increased slightly; however, it remained unchanged under the T 3 treatment. The EC se (Electrical Conductivity) of the soil increased, whereas, the pH value of the soil decreased under all the treatments. Statistically, significant difference (p 0.05) under the three treatments. Accordingly, to make profitable use of SWTs, improve WUE and productivity, and maintain soil fertility, the depth of SWT be controlled at 75 cm for growing of the Okra crop. Adapting to this guideline will help in availing the maximum contribution of SWTs towards meeting the CWR and achieve the larger aim of water conservation.

Assessing potential land suitable for surface irrigation using groundwater in Ethiopia

Although Ethiopia has abundant land for irrigation, only a fraction of its potential land is being utilized. This study evaluates suitability of lands for irrigation using groundwater in Ethiopia using GIS-based Multi-Criteria Evaluation (MCE) techniques in order to enhance the country's agricultural industry. Key factors that significantly affect irrigation suitability evaluated in this study include physical land features (land use, soil, and slope), climate (rainfall and evapotranspiration), and market access (proximity to roads and access to market). These factors were weighted using a pair-wise comparison matrix, then reclassified and overlaid to identify suitable areas for groundwater irrigation using a 1-km grid. Groundwater data from the British Geological Survey were used to estimate the groundwater potential, which indicates the corresponding irrigation potential for major crops. Results indicated that more than 6 million ha of land are suitable for irrigation in Ethiopia. A large portion of the irrigable land is located in the Abbay, Rift Valley, Omo Ghibe, and Awash River basins. These basins have access to shallow groundwater (i.e., depth of groundwater less than 20 m from the surface) making it easier to extract. The comparison between available groundwater and total crop water requirements indicate that groundwater alone may not be sufficient to supply all suitable land. The study estimates that only 8% of the suitable land can be irrigated with the available shallow groundwater. However, groundwater is a viable option for supplementing surface water resources for irrigation in several basins in the country.

Regional variation in agricultural water demand and water availability in Uttar Pradesh, India

Water is one of the important and scarce natural resource that triggers the growth of crop production. But water availability varies from the region to region depending upon the rainfall, geological formation etc. Due to growing demand of water for various uses and erratic rainfall,the water availability for crop production declining very fast in different regions of Uttar Pradesh. Water scarcity is becoming a serious challenge for government, researchers, economist and policy makers. Much effort is being made to reduce water use by crops and produce ‘more crop per drop’. Present study was an attempt to find out region-wise consumptive water demand for crop production and water availability. The study was based on secondary data. The CropWat model was used to find out the crop water requirement. Results suggests that total water demand for Eastern region, Central region, Bundelkhand region and Western region and it was found to be 70478, 38366,13790, 64703 MCM, respectively. Out of total crop water requirement, the highest share comes from wheat, rice and sugarcane in Eastern and Central region. In the Eastern region the share of crop water requirement for wheat, rice (k) and sugarcane was estimated to be 92.93 per cent of the total crop water requirement, whereas in case of Central region it was 87.64 per cent to total crop water demand. In Western region share of water requirement for growing wheat, sugarcane and rice (k) to total crop water requirement was estimated to be 88.79 per cent. During 2013–14, the annual water availability was found more than the crop water demand for Eastern, Central and Bundelkhand region, whereas in case of Western region water demand for crop production was more than the water supply from all the sources.

Remote Sensing Based Estimation of Evapo-Transpiration Using Selected Algorithms: The Case of Wonji Shoa Sugar Cane Estate, Ethiopia

Remote sensing datasets are increasingly being used to provide spatially explicit large scale evapotranspiration (ET) estimates. The focus of this study was to estimate and thematically map on a pixel-by-pixel basis, the actual evapotranspiration (ET_a) of the Wonji Shoa Sugarcane Estate using the Surface Energy Balance Algorithm for Land (SEBAL), Simplified Surface Energy Balance (SSEB) and Operational Simplified Surface Energy Balance (SSEBop) algorithms. The results obtained revealed that the ranges of the daily ETa estimated on January 25, February 26, September 06 and October 08, 2002 using SEBAL were 0.0 - 6.85, 0.0 – 9.36, 0.0 – 3.61, 0.0 – 6.83 mm/day; using SSEB 0.0 - 6.78, 0.0 – 7.81, 0.0 – 3.65, 0.0 – 6.46 mm/day, and SSEBop were 0.05 - 8.25, 0.0 – 8.82, 0.2 – 4.0, 0.0 – 7.40 mm/day, respectively. The Root Mean Square Error (RMSE) values between SSEB and SEBAL, SSEBop and SEBAL, and SSEB and SSEBop were 0.548, 0.548, and 0.99 for January 25, 2002; 0.739, 0.753, and 0.994 for February 26, 2002;0.847, 0.846, and 0.999 for September 06, 2002; 0.573, 0.573, and 1.00 for October 08, 2002, respectively. The standard deviation of ET_a over the sugarcane estate showed high spatio-temporal variability perhaps due to soil moisture variability and surface cover. The three algorithm results showed that well watered sugarcane fields in the mid-season growing stage of the crop had higher ET_a values compared with the other dry agricultural fields confirming that they consumptively use more water. Generally during the dry season, ET_a is limited to water surplus areas only and in wet season, ET_a was high throughout the entire sugarcane estate. The evaporation fraction (ETrF) results also followed the same pattern as the daily ET_a over the sugarcane estate. The total crop and irrigation water requirement and effective rainfall estimated using the Cropwat model were 2468.8, 2061.6 and 423.8 mm/yr for January 2001 planted and 2281.9, 1851.0 and 437.8 mm/yr for March 2001 planted sugarcanes, respectively. The mean annual ET_a estimated for the whole estate were 107 Mm³, 140 Mm³, and 178 Mm³ using SEBAL, SSEB, and SSEBop, respectively. Even though the algorithms should be validated through field observation, they have potential to be used for effective estimation of ET in the sugarcane estate.

Effects of temperature and growing seasons on crop water requirement: implications on water savings

Water savings can be improved through reducing agricultural water consumption. The crop water requirement (CWR) depends on several factors including temperature and growing seasons. This study investigated the effects of temperature and growing seasons on CWR in Saudi Arabia. Increase in temperature by 1°C increased the CWR by 1.9 - 2.9%, 1.9 – 3.0% and 2.2 – 3.8% for dates, alfalfa and wheat respectively. Total CWR was estimated to be 8713 million cubic meters in 2011, which showed an increase of 1.8 – 2.9% for 1°C increase in temperature. CWR for wheat was more sensitive to growing seasons than dates and alfalfa. Empirical relationship was developed to predict the effects of growing seasons on CWR for wheat while changes in CWR for dates and alfalfa were not significant. Through shifting growing seasons and minimizing the effects of temperature for the major crops, significant amount of groundwater may be saved, which can reduce the production of costly desalinated water. Keywords: Water resources; conservation; crop water requirement; temperature; growing seasons; policy

Determination of Optimal Irrigation Scheduling for Maize (Zea Mays) at Teppi, Southwest of Ethiopia

Appropriate irrigation practice is relevant for increased crop productivity and conservation of water resources. No or little concern has been given to the necessity and extension of existing irrigation technologies while the impacts of climate change are visible throughout Ethiopia. A field study was carried out for determining optimal irrigation scheduling for maize production at Teppi, South west Ethiopia for three successive years. The objectives of the study were to evaluate the effect of different irrigation regime (different soil moisture depletion levels) on yield and water use efficiency of hybrid maize (BH-140). The treatments were set based on the recommended soil moisture depletion levels for maize (MAD=0.55). Then five levels of soil moisture depletion were selected for evaluation of optimum irrigation scheduling namely SMD1 (60%), SMD2 (80%), SMD3 (100%), SMD4 (120%), and SMD5 (140% of the recommended value, 0.55). The result indicated that SMD4 has significantly (P<0.05) increased the grain yield and water use efficiency of maize crop on a clay loam textured soil. In addition the total crop water requirement was 535.60 mm. However, the reduced soil moisture depletion level below the recommended values (SMD1 and SMD2) has resulted lower both grain yield and crop water use efficiency. This study also revealed that the appropriate irrigation interval at each crop growth stage should be identified for ease of work to the users.

Modeling water requirements of major crops and their responses to climate change in the North China Plain

The North China Plain (NCP) is one of the most important food production bases in China. However, its agriculture water resources are threatened by climate change. In this paper, the CROPWAT model is used to evaluate crop water requirement (CWR), crop green water requirement (CGWR), and crop blue water requirement (CBWR) for main crops in NCP (winter wheat, summer maize, cotton, millet, and soybean) with a spatial resolution of 5 arc-minute from 1961 to 2010. Their responses to future climate changes are investigated. The results show that the mean annual total CWR of the main crops during growing periods amounted to 114.68 km3 a−1 in the past 50 years. More than 72 % of CWR to support NCP crop production is green water. The spatial distributions of CWR, CGWR, and CBWR are closely related to the planting areas and irrigation availability. Summer maize, millet, and soybean are high CGWR crops with proportions of above 84 %, while the lowest CGWR proportion is in winter wheat, 58.89 %. For climate change impacts in future, holding the crop planting system and irrigation conditions unchanged, it is projected that the total CWR in 2030s will require approximately 8.75–11.25 km3 a−1 additional water. Results show that the CWR increase in 2030s is mainly due to the increase in temperature. Under the projected temperature in 2030s and the current rainfall scenario, total CWR, CGWR, and CBWR increments were 8.58, 1.76, and 6.82 km3 a−1, respectively. Nearly 80 % of the CWR increment is from the increase in CBWR. Therefore, agricultural water shortage crisis will further aggravate under future climate change scenarios in NCP, and effective water-saving measures must be taken to mitigate the negative effects of climate change.