Penman Method Research Articles

Evaluating potential evapotranspiration methods in a rapidly warming Arctic region, SW Spitsbergen (1983–2023)

Study regionsHornsund, SW Spitsbergen, Svalbard – area representing atlantic sector of High Arctic Study focusSvalbard's warming climate significantly alters its hydrological conditions. Evapotranspiration, a crucial hydrological component, is understudied in this High Arctic environment. In this study, daily potential evapotranspiration (PET) estimates for the period 1983–2023 were calculated using meteorological data from the Polish Polar Station Hornsund (SW Spitsbergen). 11 different PET methods were applied, those include radiation-based, temperature-based, radiation-temperature-based, and combined methods. New hydrological insights for the regionThe results show a large spread in the annual sum of PET ranging from ∼20 mm/y (Kharrufa) through ∼300 mm/y (Penman-Monteith) up to ∼450 mm/y (Abtew). Trends analysis shows different outcomes depending on the length of the averaging period. Using a daily timescale, PET methods tend to show more similar patterns of changes than using monthly timescales. The changes in PET estimates differ between the models, hence classifying PET methods should consider their sensitivity to meteorological changes. PET estimates were compared with pan measurements at a daily time scale in 2022–2023. The Penman method produced the best results in relation to pan measurements. In other cases, despite a relatively high linear correlation, calibration to local conditions is needed to scale the outcomes and limit biases. This study improves understanding of how PET models perform in the rapidly changing High Arctic climate.

Priestly-Taylor Coefficient Evaluation for Konya Closed Basin

Measurement of evaporation in the field is difficult and expensive; thus, the empirical evaporation estimation methods have been developed. However, these estimation methods have both advantages and disadvantages. The main disadvantage is that their coefficients were determined by the climatic conditions of the study areas. One of these methods is Penman. The Penman method, accepted as a reference, has reached the closest estimations to the measurement of evaporation in the field of the different parts of the world. However, it needs lots of measured climatic data. The Priestley-Taylor method was derived to reduce the measured data needs of the Penman method. Priestly and Taylor represented the variables such as saturated and actual vapor pressures and wind speed with coefficient of 1.26. The researchers have continued to study on the calibration of the  coefficient for their studies’ area since this method has been known to underestimate evaporation value in areas where advection is effective. The present study consists of two stages. First, evaporation was tried to be estimated with these two methods by using the measured climatic data of five meteorological stations in the Konya Closed Basin. Estimated values were evaluated making comparison with the pan measurements. Although slightly higher values were estimated from the pan measurements with each method, the Penman method was found to be relatively more consistent on the basis of statistical indicators. Second,  coefficient was obtained as 1.28 for the study area by using three artificial intelligence-based optimization algorithms. The Penman method was used for comparison in this stage. It was concluded that there was no need for any calibration of the  coefficient and the original one was found to be valid for the study area as well.

STUDY OF IMPROVING THE IRRIGATION NETWORK SYSTEM FOR THE SALURAN INDUK MADIUN (SIM) IN MAGETAN REGENCY

The Saluran Induk Madiun, abbreviated as SIM, is the primary waterway that irrigates the SIM Irrigation Area. Jati Dam, located in Gondangan Village, Gorang-Gareng District, Magetan Regency, is the primary source of the SIM Irrigation Area. This SIM Irrigation Area gets its main supply from Jati Dam; Jati Dam is the upstream or the beginning of the flow in the SIM Irrigation Area. In conditions before rehabilitation, the Jati Dam had a discharge of 4000 l/s to irrigate the entire SIM Irrigation Area. Especially for the SIM Irrigation Area in Magetan Regency, obtaining water supply from the Jati Dam at 17% of 350,746 l/s, the discharge value can only meet the paddy cropping pattern of 30%. Looking at these problems, the Government of Indonesia is seeking rehabilitation work to increase agricultural barns production. Therefore, it is necessary to research the improvement of irrigation network systems to determine the ratio of water availability before and after rehabilitation, water demand, and the value of increasing agricultural profits. This research uses the F.J. Mock to assess the availability of water discharge FAO Modified Penman Method and the amount of evapotranspiration used to analyze water demand for each cropping pattern. A comparison of the value of the availability and demand for water is presented in the form of a water balance.From the results of the analysis that has been carried out, it is concluded that the highest water availability in the SIM Irrigation Area in Magetan Regency before rehabilitation was 1.37 m3/sec, and the lowest was 0.74 m3/sec. In conditions after rehabilitation, the highest was 5.75 m3/sec, and the lowest was 4.64 m3/sec. It is known that the supply from the Jati Dam, in conditions before rehabilitation, was 17%, and in conditions after rehabilitation, it increased to 28%. The highest irrigation water requirement is the cropping pattern that uses 100% paddy of 3.01 m3/sec. Seeing the value of water availability compared to the still significant water demand, the Jati Dam intake can be reduced from 28% to 20% so that the remaining water can be distributed to the following secondary waterways. Water availability at a percentage of 28% is 5.75 m3/sec; at 20%, it becomes 3.49 m3/sec. This debit can fulfill the highest water demand of 3.01 m3/sec. In conditions before rehabilitation, the availability of water was only able to meet the planting pattern of Paddy (30%) - Paddy (25%) - Secondary crops (100%) with a profit of Rp.26,161,069,519.00. Whereas in conditions after rehabilitation, the availability of water can fulfill the planting pattern of Paddy (100%) - Paddy (100%) - Paddy (100%) with a profit reach up to Rp.115,325,883,740.00.

Assessing the Reliability of Satellite-Derived Evapotranspiration Data Using Numerical Modified Penman Method at Citarum Watershed

Evapotranspiration is an essential part of water availability analysis and crop water needs that are useful to estimate irrigation water demand. Since discharge measurement stations are limited, the analysis of water availability is the most important part of water management planning. Citarum watershed is the biggest watershed in West Java, supplies raw water to Jakarta, the capital city of Indonesia. Modified Penman is the common equation to analyze evapotranspiration, which was developed by Food and Agriculture Organization (FAO) and modified for tropical areas. Evapotranspiration is one term of the water balance equation. To determine water losses, it is necessary to solve this equation. Another source of evapotranspiration data is provided by the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite's standard product, MOD16A2. In order to used the evapotranspiration satelilite data to fullfill the lack of groud station data, the reliability of satelite data is needed. The objective of this study is to compares and analyzes the reliability of satellite evapotranspiration potential images with the numerical Modified Penman method at Citarum Watershed. Modified Penman is one of several methods that calculate the evapotranspiration potential based on climate data. MOD16A2 was used for simulation data, and Modified Penman was used for baseline data. The reliability of the two simulations was analyzed by the skewness percentage of each pixel and period. The distribution of percent skewness indicates the performance of satellite evapotranspiration on the Modified Penman that represents the actual condition. The sensitivity of satellites is greatly affected by local weather conditions.

Ketersediaan dan Kebutuhan Air Daerah Irigasi Ameroro Kabupaten Konawe

In general, sources of agricultural irrigation in Indonesia still rely on rainwater, so the productivity of wetland agriculture, especially rice, is highly dependent on rainwater as an agricultural input. In this position, irrigation (weirs) is important in maintaining the availability of water for agricultural irrigation needs. This study aims to analyze water availability and water demand from Ameroro Irrigation. Both of these results provide information (pattern) of farmer planting. Research data comes from primary and secondary. Comparative analysis of the supply and demand for irrigation water using the Penman method and the F.J. Mock method to determine the amount of water flow from rainfall data, the hydrological characteristics of the catchment area, and evapotranspiration. The results of this study position that the construction of the Ameroro Dam has a vital role in maintaining the balance of irrigation (inflow and outflow). Maintaining this balance is at the same time the basis for irrigation engineering management efforts for agricultural activities. For farmers, those who live on or cultivate functional agricultural land A, B, and C start the planting season in May or in another month taking into account that the maximum plant growth period does not occur in the October period.

ANALISIS KEBUTUHAN AIR TANAMAN SELADA (Lactuca sativa L.) PADA INCEPTISOL DAN VERTISOL BERBASIS INTERNET OF THINGS (IoT)

Lactuca sativa L. has good economic prospects, but lettuce production often declines due to the unmet water requirement of lettuce. This study aimed to determine the water needs of lettuce on Inceptisol and Vertisol based on the Internet of Things (IoT). The location study was in the green house, Huluduotamo Village, Bone Bolango Regency, from September to October 2021, while the Vertisol and Inceptisol samples were from Sidomukti Village, Gorontalo Regency. This study used the Penman method with the Cropwat 8.0 application which was integrated with a smartphone through the Blynk (IoT) application. The water requirement yield of lettuce plants in September on Vertisol and Inceptisol in the early phase was 2.45 mm/day, the middle phase was 3.73 mm/day, and the final phase was 3.54 mm/day. Soil moisture detection device at field capacity moisture content produces 319 Analog Digital Converter (ADC) and soil in moist conditions reaches 534 ADC. The analog data value of the water content of the Inceptisol field capacity is 343 ADC and the soil in a moist state is 574 ADC. The performance of the device for detecting soil moisture in the water condition of the 15% field capacity of Vertisol and 22% Inceptisol is more effective than the gravimetric method.

Prediction of Streamflow of the Anai-Weir Catchment Using Both the SWAT and Mock Models

This research focuses on predicting the streamflow of the Anai-weir catchment using the SWAT (Soil and Water Assessment Tools) and Mock models. The catchment studied is approximately 34,024 ha wide. The rainfall and climatological data were collected from the three nearest rainfall stations, namely Kandang IV (13.8 km far), Kasang (15.2 km far), and Sicincin Stations (11.2 km far), from 2010 to 2019. The first research methodology is to delineate the catchment, form a Hydrologic Response Unit (HRU), and then enter the climatological data into the SWAT model to estimate the daily streamflow. This daily streamflow is then averaged over a semi-monthly period. The second research methodology is to estimate an evapotranspiration depth based on the climatological data using the Modified Penman method, and then predict the semi-monthly average-daily streamflow using the Mock model. The results obtained from both methods are then compared with the Anai-weir AWLR-data. The average results from each method, namely, the SWAT model, the Mock model, and the AWLR data have the same tendency, but the Mock model results are closer than the SWAT model results to the AWLR data. This indicates that the Mock model is more suitable than the SWAT model for the existing data conditions. Even though the SWAT model considers more variables than the Mock model does.

Evaluation of water balance in the Jaro Irrigation area, Tabalong Regency, South Kalimantan Province

In the Tabalong Regency, South Kalimantan Province, many irrigation networks have not worked optimally. The Jaro Irrigation Area is one of these irrigation networks, the majority of available fields are planted with Paddy. Evaluation of irrigation water to irrigate paddy fields is very important for optimal growth and development of paddy. The objective of this research is to evaluate the water balance, the potential area for paddy field area development can be obtained by applying the optimal crop pattern. Analysis of the rainfall data used in this study with statistical analysis in the form of validation and correction of rainfall data. Rainfall data was obtained from the Tropical Rainfall Measurement Mission (TRMM) and the Meteorology, Climatology, and Geophysics Agency (BMKG) Jaro Station in the period 2013-2019, the data using statistical analysis obtained a correlation coefficient and regression equation. The regression equation is used to obtain the corrected rainfall value which will be used in the hydrological analysis. Water requirement analysis with several cropping pattern scenarios. Calculation of evapotranspiration using the Modified Penman method. The F.J Mock method is used to develop the discharge value. Dependable discharge, 80%, is used to estimate water availability. Furthermore, an evaluation of the water balance is carried out for each scenario, and the result of information on surplus or deficit conditions can be obtained each month. Analysis of water demand discharge based on planting scenarios is divided into three. First Scenario with a high-yield paddy - a high-yield paddy according to the existing conditions at the research location. The second scenario is with a high-yield paddy - high-yield paddy - beans and the third scenario is with a high-yield paddy - paddy. According to the results of the water balance evaluation for the three scenarios, the potential area can be reached up to 900 ha from 850 ha with the chosen crop pattern in scenario number 2.

Kebutuhan Air Irigasi pada D.I Krueng Pasee Aceh Utara

Water demand is the amount of water volume that must be met for irrigation, in the Krueng Pasee irrigation area of North Aceh has an irrigation network area of 5579 Ha. The purpose ofthis research is to obtain the maximum and minimum irrigation water demand discharge in the study area. This research can be an additional source of knowledge for writers in particular and for readers in general. As well as the results of this study can be known the value of rice planting water needs. The data used in the research is rainfall data sourced from BMKG (Meteorology, Climatology, and Geophysics Agency) Malikussaleh, used to calculate effective rainfall and climate data sourced from BMKGMalikussaleh in the form of temperature data, solar irradiation data, wind speed data and humidity or temperature data used to calculate evapotranspiration (ETo). ETo is a combination of evaporation and transpiration which is defined as the event of water loss from plant tissue and the surface of the soil usedas a place to grow plants. In analyzing ETo using the Penman Modification Methodology. The Penman method by adjusting the wind function according to local conditions produces the best approach to the evapotranspiration rate of the lysimeter results. The consumptive use of plants (ETc) during the land preparation period uses the results of the calculation of water requirements for land preparation (IR). Crop consumptive use (ETc) after land preparation is a calculation between evapotranspiration and cropcoefficient. The calculated irrigation water requirement (NFR) results in water requirement in the form of mm/day. Irrigation water requirements are converted to l/dt/ha with a conversion rate of 1/8.64. The smallest water demand calculation discharge was obtained in November-1 at Q = 4.32 m3/det and thelargest water demand in February -1 at Q = 13.40 m3/det. At the research location, rice planting begins in January-I, with a rice-soybean planting pattern. From the calculation of water demand, Krueng Pasee Irrigation Area has the smallest water demand in November-1 and the largest water demand in February-1.

Evaporation from snow surface: A multi-model evaluation with the FLUXNET2015 dataset

Evaporation from snow surfaces (Ess) is a critical component of snow mass balance, and its accurate estimation is essential for the water balance at high latitudes and altitudes. Selecting an appropriate model is important for achieving an accurate estimation of Ess. However, there have been few studies focused on the choice of Ess models. In this study, we evaluated six commonly used Ess models at twelve eddy covariance sites in the FLUXNET2015 dataset. The six models considered include an empirical method (EM), two bulk aerodynamic (BA) methods, two energy-based models (maximum entropy production (MEP) model and Priestley-Taylor (PT) model), and a combination model (Penman model). The results show that the performance of the six models differs significantly, and no single model consistently outperforms the others across all sites. Overall, the Penman method performs the best on both the hourly and daily scales with Kling-Gupta efficiency (KGE) coefficients of 0.75 and 0.65 on the two timescales, respectively. Therefore, we recommended the Penman model as the preferred model for Ess estimation. In the absence of net radiation data, we suggested using the EM model as it noticeably outperforms the other four models. The reason for the poor performance of the two BA models, with KGE values less than 0.4, may be attributed to their unreasonable parameterization of atmospheric stability. On the other hand, ignoring or simplifying the aerodynamic term is likely responsible for the poor performance of the MEP and PT models.

EVALUASI KEBUTUHAN DAN KETERSEDIAAN AIR IRIGASI DALAM RANGKA PENINGKATAN HASIL PERTANIAN

The availability of water in irrigation areas can affect agricultural productivity. Water balance must be maintained so that there is no shortage of water. Cikunten II has an area of 4.362 ha, mostly in the Tasikmalaya district. This study aims to analyze the water requirement and balance. Data analysis used the KP01 guidelines and the Cropwat program. The data analysis results obtained differences in reference plants' evapotranspiration results using the Modified Penman method in KP and Pennman–Monteith in the Cropwat program. The difference between the two methods is 133,83% due to the difference in albedo coefficients. The effective rainfall for paddy and secondary crops, the KP method analysis is lower than the Cropwat simulation of 110.10%. Availability of water using data from the Ciwulan weir with a reliability of 80% obtained a maximum discharge of 2,73 m3/sec. The water requirement was calculated during planting periods I, II, and II. The KP method is greater than the Cropwat method with a percentage of 277.42% in analyzing water requirements in the Paddy-Paddy-plants cropping pattern. The availability of water in the Cikunten area using Cropwat has fulfilled the needs marked by a more stable k factor than the KP01 method.

Performance evaluation of evapotranspiration estimation methods in Sultanpur, Uttar Pradesh, India

Accurate estimation of evapotranspiration plays a vital role in judicious irrigation scheduling. Keeping this in view, a study was undertaken to compare the performance of five methods, viz. Penman method (PM), FAO Penman Monteith (FAO-PM), Priestley-Taylor (PT), FAO Radiation method (FAO-RM) and Hargreaves methods (HM) for Sultanpur District of Uttar Pradesh, India using the daily weather data acquired from automatic weather station during 2016-17. The performance evaluation of selected methods was carried out using linear regression and simple statistical analysis to suggest a substitute of FAO-PM for estimation of reference evapotranspiration using minimal climatic parameters available at regional scales. It was observed that the PM method performed the best and was in line with estimated ET0 by FAO-PM method with coefficient of determination (R2), Root Mean Square Error (RMSE), Mean Absolute Error (MAE), Modified Nash-Sutcliffe Coefficient (EMNS), Percent Bias (PBIAS) estimated as 0.94, 0.54, 0.40, 0.73, 3.74 for the year 2016 and 0.95, 0.44, 0.36, 0.73, 6.01 in 2017, respectively. Nonetheless, it was observed form this study that the PM method which requires four parameters, viz. daily solar radiation, maximum and minimum air temperature, and wind speed can be a substitute to FAO-PM that require more parameters for ET0 estimation in data scarce situations.

Analysis of water balance and hydrodynamics of Lake Beseka, Ethiopia

Abstract This study aims to calculate the water balance, interaction with irrigation water inflow, and hydrodynamics of Lake Beseka by a spreadsheet-based model using climatic, hydrological, multi-temporal satellite images, groundwater, and lake chemistry data. The rainfall for the catchment was estimated as 558.4 mm/year, whereas the mean evaporation was computed as 2,214 mm/year by the Penman method. The annual direct rainfall contribution to the lake was found to be 25.84 MCM (million cubic meters) with a runoff inflow in the catchment area of 37.2 MCM. This balance pointed to the mean evaporation of 108.2 MCM/year in the lake indicating that the water inflow was greater than the outflow. A major cause for the rise of the lake level was the drainage of excess irrigation water toward the lake, mainly from the Fentale Irrigation Farm. The average increment of the groundwater level in the area was 12 cm/year from 2010 to 2014. From 1998 to 2014, the electrical conductivity was reduced by 25.6%, and calcium was increased by 96%. The study outlined that appropriate irrigation drainage should be implemented in the catchment to ensure the balance between the rainfall, infiltration, and surface runoff to optimize economic and social welfare in the area.

Estimation of crop water requirement for Bargi left bank canal command area-Jabalpur M.P. India

Effective water management methods are needed to maximize crop yield that required calculating crop water requirement correctly. Evapotranspiration is the main component of hydrological cycle, so it is important to estimate this component in an accurate manner which is necessary for many hydrological studies. The water requirement of any crop can be estimated by multiplying reference crop evapotranspiration with crop coefficient values. Various method of estimation evapotranspiration is available at present. However, in this paper the best method is focused to compute evapotranspiration for crop water requirement. It was found that the wheat has the highest water requirement whereas maize has the minimum water requirement throughout the periods and the February month requires the maximum supply of water. The Gross water requirement is found out to be 16,082,177.24 m3 per year and 5,064,098.5 m3 per year by Blaney Criddle Method and modified Penman method respectively.

Identifying Reservoirs and Estimating Evaporation Losses in a Large Arid Inland Basin in Northwestern China

Reservoirs play a vital role in agricultural irrigation, food security, and ecological protection in arid and semi–arid areas where water resources are scarce. In the Tarim Basin (TB) in northwestern China, a large number of reservoirs have been built or are being built, resulting in significant evaporation losses. However, information about the distribution, area and evaporation rate of the reservoirs in TB is limited. To contribute, we present an inventory of reservoirs and calculate their monthly surface area and evaporation rate during the study period of 1990–2019, using the TerraClimate dataset, Google Earth Engine (GEE) platform, Landtrendr algorithm, Penman method, and Landsat images. The results suggest: (1) The inventory of 167 reservoirs in TB consists of 142 existing reservoirs (built before 1990), 5 new reservoirs (mountain reservoirs, built during 1990–2019), and 20 dried–up reservoirs (plain reservoirs that went extinct during 1990–2019). (2) The reservoir types in TB are mainly plain reservoirs with an altitude of less than 1500 m and an area of less than 10 km2, accounting for about 88% of the total number of reservoirs. (3) The surface area of the reservoirs increased at a significant rate (p < 0.05) of 12.45 km2/y from 401 km2 in 1990 to 766 km2 in 2019. (4) The evaporation rate of the reservoirs increased at a slight trend of 0.004 mm/d/a and varied from 2.57 mm/d in 1990 to 2.39 mm/d in 2019. Lastly, (5) The evaporation losses of reservoirs in TB significantly increased (p < 0.05) from 4.72 × 108 m3 to 4.92 × 108 m3 due to the significant increase in reservoir surface area (p < 0.05) and the slight increase in evaporation rate from 1990 to 2019. This study provides essentials of the reservoir inventory, surface area, and evaporation rate with considerable baseline inferences for TB that may be beneficial for long–term investigations and assist in local water resources decision support and sustainable management in arid regions.

Comparison of evaporation estimation methods for water surface under floating coverage in arid areas

The main purpose of this study is to evaluate evaporation estimation methods for water surfaces under floating coverage in arid areas. The natural water surface evaporation methods (namely, the mass transfer method (MT), Bowen ratio energy balance (BREB) method, Penman method, the Penman-Monteith method (PM), and the Priestley-Taylor method (PT)) are corrected to establish the covered water surface evaporation methods, which are based on the micrometeorology near the covered water surface, energy balance components, and Bowen ratio. The radiation term of the natural water surface evaporation model is corrected by introducing the Bowen ratio of the entire surface, which includes the uncovered water surface and the floating cover surface. The mass transfer coefficient and aerodynamic impedance in the aerodynamic terms of the natural water surface evaporation model were corrected. Taking the evaporation of the water surface covered by spheres (coverage rate of spheres is 76.4%) as an example, based on the rose change characteristics of the above parameters, the effects of these modified evaporation models are comprehensively evaluated from three different time scales (even months, odd months and the complete test period). The evaluation methods include the root mean square error (RMSE), index of agreement (D), mean bias error (MBE), and coefficient of determination (R2). The results show that under three different time scales, the Penman-Monteith model is the most promising and superior in estimating water surface evaporation under floating coverage (for the complete test period, RMSE=0.11 mm·d−1, D=0.99, MBE= 0.07 mm·d−1, and R2 =0.99); the Priestley-Taylor model is slightly less effective in estimating evaporation than the Penman-Monteith model, and the mass transfer model and the Penman model are less effective in estimating evaporation. Furthermore, the analysis of the Penman-Monteith model shows that the evaporation of the radiation term (69.5%) is higher than that of the aerodynamic term (30.5%) during the evaporation of the water surface under floating coverage, while the evaporation of the radiation term is dominant. Moreover, during the complete test period, the weights of the radiation evaporation and aerodynamic evaporation changed significantly with time. The proportion of radiation evaporation varies from 54.8% to 81.7%, while that of aerodynamic evaporation varies from 18.3% to 45.2%.

Assessment on spatial extent of arid and semi-arid climatic zones of India using GIS


 In this study, a quantitative assessment of spatial extent of arid and semi-arid climatic zones of India was performed for the period from 1988 to 2018 using potential evapo-transpiration (PET) calculated by Modified Penman Method, estimated from global climate data sets. Climatic water balances computed for 625 stations across the country are used for classifying to bio-climate types based on moisture index and areas falling under arid climatic zones in India are delineated using ArcGIS 10.5. It was noticed a considerable changes in the country’s arid and semi-arid climatic zones between the two periods; 1992 and 2018. Overall, there has been a net percent change in hyper arid, typic arid and semi arid (dry) areas is 5.62, 1.62 and 7.17 percent, respectively. Dryness and wetness are increasing in different parts of the country. There is also change in rainfall, PET and moisture index over a period of time which is vital to determine aridity pattern of any region. Thus, results are of great significance for studying the assessment of temporal and spatial dry climatic water balance of India, which can help immensely in the management of water resources and sustainability of crop production under changing climatic conditions.

DIFFERENT METHODS FOR MEASURING EVAPORATION IN A TROPICAL RESERVOIR: THE CASE OF THE GAVIÃO RESERVOIR IN THE STATE OF CEARÁ

ABSTRACT Studies that allow the estimation of evaporation in reservoirs represent an important action for the adequate management of water resources. Thus, this study aimed at estimating evaporation in the tropical reservoir Gavião, located in the municipality of Pacatuba, Ceará, Brazil, and to verify the effect of these estimates on the water availability of the reservoir using the VYELAS model. The results of Penman's methods and the Water Balance were compared with the values obtained from the hydrostatic pressure sensor, the most accurate. It was possible to verify that, in relation to the pressure difference method, all the conventional methods overestimate the evaporation in the reservoir. The method that presented estimates closer to those obtained by the pressure difference sensor was that of Penman, based on data from an onboard station in the lake, with a deviation of only 12%. The method of water balance also presented reliable results for monthly average. The two methods usually accepted in the evaporation calculation (water balance ignoring the infiltration; and Penman's method for meteorological station data on land distant from the lake) presented the most disturbing evaporation values significantly altering the water availability. The results of the VYELAS model showed that evaporated flows, estimated by several methods, exceeded the reference flow by up to 83%. The results demonstrate the great sensitivity of the estimate of water availability in relation to the evaporation rate in the lake.

ANALISA KETERSEDIAAN DEBIT AIR SUNGAI CIBUNI MENGGUNAKAN METODE F.J MOCK DAN NRECA

In a hydropower planning plan, an important factor that must be known is: the amount of monthly discharge and flagship discharge, as well as the river canfography. To calculate the amount of water availability in Cibuni watershed for the needs of the PLTMH, the discharge analysis of the F.J MCOK method and the NRECA method and the magnitude of the potential evapotranspiration use the Penman method. Hujang bulk data used is rainfall data obtained from 5 rain stations in the form of monthly rainfall for 16 years from 1996-2011. From the calculation of the F.J Mock method for the availability of water in Cibuni Das, a maximum discharge of 28.46 m3 / dt and minimum water discharge of 0.11 m3 / dt. As for the NRECA method is a maximum water discharge of 26.50 m3 / dt and minimum water discharge of 2.77 m3 / dt. Based on the calculation results, for the F.J Mock method is more suitable for use in Cibuni watershed compared to Nreca.

The needs and availability analysis of irrigation water of Way Wayah Irrigation Area

Optimization of agricultural land is an effort to mprove and increase land support capacity, in such a way become more productive farmland. The Local Government of Pringsewu Regency planned to develop irrigation network by utilizing Way Wayah river. This study aims to design irrigation area in Way Wayah and to analyse water availability of Way Wayah river and water need of the planned irrigation area. Irrigation network design includes analysis of determining the location of the weir, so that it can be estimated the area of designed paddy field, the catchment area as well as the availability of water resources. Analysis includes spatial analysis using Geographical Information System, hydrologic analysis for water availability and Penman method for irrigation water need. The results show that (1) the planned weir will be located in Giri Tunggal with catchment area of 7,238.9 ha, the area of total paddy rice fields (existing and planned paddy rice fields) is 960.46 ha; (2) The need for water are 6196.88 m3 ha-1 season-1 and 6556.96 m3 ha-1 season-1 for planting seasons 1 and 2 respectively. Water availability is sufficient during preparation and planting periods