A geographic information system (GIS) based graphical user interface for irrigation management within an ArcGIS customization has been developed using Visual Basic for Applications for estimation of spatially distributed irrigation water requirements. It is capable of providing an appropriate framework for manipulating, visualizing and analyzing spatial data to support decision making in irrigation management. Its application is demonstrated through a case study for use in the field.
Irrigation is one of the most important inputs for efficient and sustainable agricultural production (Gundogdu et al. 2002; Ortega et al. 2005). According to the Food and Agriculture Organization (FAO), one of the biggest challenges for agriculture in the coming decades will be to ensure food security for the world's steadily growing population (Bergez et al. 2012). Proper management of an irrigation system reduces water demand, which leads to water saving for other uses, improves agricultural productivity, and further helps in reduction of the environmental impact of irrigation (Hargreaves et al. 1985; Suryavanshi & Reddy 1986; Bastiaanssen et al. 2000). Irrigation management is therefore of paramount importance to irrigation professionals/planners/managers, for it involves multi-tasks and multi-stakeholders with varying goals. It is of common experience that spatial and temporal variabilities create problems for traditional irrigation management support systems (Lin et al. 2004).
Customization of geographic information systems (GIS) with Visual Basic for Applications (VBA) can be a solution for irrigation management. Most of the data related to irrigation management is complex as it is both temporally and spatially distributed in nature (Pervez & Hoque 2008; Naidu & Giridhar 2011). Its integration has led to the introduction of GIS and other technologies (Martin 1996; Bastiaanssen & Bos 1999; Bioggio & Ding 2001; Kjelds & Storm 2001; Nixon et al. 2001; Su & Wen 2001; Ray et al. 2002; Liang & Wu 2012) in irrigation management. GIS play an important role in transferring information in easily communicable form, such as maps, to farmers, planners and experts for irrigation planning and management (Maguire et al. 1991; Goodchild 1992; Ray et al. 2000; Muthanna & Amin 2003; Todorovic & Steduto 2003; Suresh Babu et al. 2012).
GIS have been widely applied in all scientific fields and practical activities. With environmental management, their use covers a broad spectrum, including a simple formula, and visualization of natural data as maps, visualization of pollutant concentrations in the environment and their spatial distribution (Gajos & Sierka 2012). Sheate et al. (2012) developed a methodology for mapping ecosystem services using GIS and readily available, existing land use/land cover datasets. Karteris et al. (2016) used GIS extensively to extrapolate the results from the building to the city scale and worked out a green sustainable strategy for the Mediterranean using environmental modelling.
ArcGIS is one of the most commonly used GIS applications in the irrigation and water resource management sectors (Tsihrintzis et al. 1996). It can be customized with the VBA development environment, which is fully supported by ArcGIS. This capability can be used to develop an essential tool for modeling of spatially distributed irrigation water requirements (Teixeira & Pereira 1992; Choudhury et al. 1994; Yamashita & Walker 1994; Hales & Burton 2000; Heinemann et al. 2002; Rao et al. 2004; Fortes et al. 2005; Lozano & Mateos 2008; Raut et al. 2008; Dhakal 2010). No such work has yet appeared in the literature in which ArcGIS customization has been developed using VBA for estimation of spatially distributed irrigation water requirements.
Thus, the present study was undertaken with the specific objective of developing a graphical user interface for irrigation management (GUIIM) within an ArcGIS customization using VBA for estimation of the spatially distributed irrigation water requirements. Its application is demonstrated through a case study area of Lakhnauta Minor of the Sidholi Distributary of the Upper Ganga Canal (UGC) system of Uttarakhand State, India through generation of thematic maps of rainfall, effective rainfall, daily reference evapotranspiration, daily crop evapotranspiration, and net irrigation requirement (NIR).
DEVELOPMENT OF INTERFACE
The development of the interface for each component is described below.
Irrigation requirement interface tool
Rainfall menu and its module
The Rainfall Raster module allows access to the rainfall layer and its rainfall field data. This module uses the rainfall layer and its rainfall field data as input and interpolates rainfall data using inverse weight techniques to produce a rainfall raster map of the area included by the points. The Effective Rainfall Raster module allows access to the rainfall layer and its effective rainfall field data. This module uses the rainfall layer and its effective rainfall field data as input and for interpolating rainfall data using the same technique to produce an effective rainfall raster map of the area included by the points.
The Rainfall Raster Fields module uses the rainfall raster map and fields polygon as a mask and extracts the rainfall raster map to produce a rainfall raster map of the study area only included by the field layer. The Peff Rainfall Raster Fields module uses the effective rainfall raster map and fields polygon as a mask and extracts the rainfall raster map to produce the rainfall raster map of the area of interest.
Reference ET (ETo) menu and its module
The Update Weather module allows the selection of a polygon layer of the cropped field and allows linking of the ETo graphical window. The ETo graphical window allows selection of the weather data from the existing station available in the database. The weather data listed in the ETo graphical window are loaded from the prepared database inside the interface and can be edited and saved for further uses. The weather data can be used for each field or can be used for all fields at once. After editing, the weather data update button allows updating and the storing of the new values.
ET0 is computed inside its graphical window through respective command buttons. Different methods of ET0 computation can be triggered by respective command buttons, as for example, the FAO Penman-Monteith equation, Irmak and Hargreaves methods. The computed ETo values appear in its fields in every row of the grid. The update command updates all the weather data and computes the ETo value in respective cells and in its database for further use. The graphical window for ETo allows updating of the weather parameter and computation of ETo (Figure 6(b)).
The Raster ETo module allow access to the field layer and its ETo field data. This module uses the rainfall layer and its ETo field data as input and produces the ETo raster map.
Crop ET (ETc) menu
The Crop ET (ETc) menu and its attached modules allow the updating and selection of the crop data, soil data and soil moisture data required for computation of the crop evapotranspiration and irrigation requirement. This menu allows generation of the thematic raster map of the crop evapotranspiration and water requirement for the selected field layer. This module allows selection of the field layer and required calculations and updating of the crop data, soil data and soil moisture data. Further, it allows development of thematic raster maps of crop evapotranspiration and water requirement for the area of interest.
The Crop ET (ETc) menu comprises two modules, namely Update Crop ET and Raster ETc (Figure 6(c)). The Update Crop ET module allows first the selection of a layer for the field. After layer selection it allows links to the ETc graphical window.
The crop data listed in the graphical window of ETc are imported from the prepared database inside the interface and can be selected for use in the soil water balance process. The computed data for crop evapotranspiration and irrigation requirement values can be used for either each field or for all fields at once and data can be updated and stored in the database using the update button. The Raster ETc module allows access to the field layer and its ETc field data in the field's layer attribute table. This module uses the field layer and its ETc field data as input and process to produce a crop evapotranspiration (ETc) raster map of the area of interest. The ETc graphical window can perform the following task regarding computation of crop evapotranspiration and irrigation requirement.
Selection and update soil type
The soil type for each field can be selected from the drop-down combo box and can be stored by the command button. The soil type can be used for each field or used for all at once through the respective command buttons. The type of soil in each field is used for computation of crop coefficient and water requirements in cropped fields.
The user is allowed to select commonly used crops through the combo box. Crop data which are not available in the combo box can also be placed by the user with values defined by the user.
Correction of Kc mid and Kc end for local climate
The Kc values (FAO paper-56, table 12) used in the interface are the typical expected values of average Kc under standard climatic conditions. For local climatic conditions the Kc value needs to be corrected. The user is allowed to make adjustments for the local or specified climate. The correction of the crop coefficient for local climate conditions is possible through the command button.
Soil water balance and allocating irrigation
By calculating the soil water balance of the root zone on a daily basis, the timing and depth of future irrigations can be estimated. The module allows users to model soil water balance in the root zone and forecasting of irrigation requirement.
Irrigation management module
The irrigation management module generates the raster map of NIR. It uses the raster map of water requirement and effective rainfall, generated by the interface, to produce a thematic raster map of net irrigation.
After development of the irrigation water requirement interface it was applied in the Lakhnauta Minor of the Sidholi Distributary of UGC of Uttarakhand State, India.
Application of the interface in UGC
Spatial database preparation
In this study, standard rice crop data were included in the interface and crop duration was inserted manually. Other crop information such as root zone depth and crop coefficient for respective development stage are stored inside the interface database and selected during execution of the interface. The selected soil type is sandy loam. It is assumed that soil is homogeneous and paddy crop is planted all over the study area.
Data preparation consists of preparation of the spatially distributed GIS data of the selected area with the polygon of the cropped field's boundary and the spatial points of the weather stations near the study area. Separate layers for each rainfall point data covering the field's layer and field's polygon layers are prepared using ArcGIS 9.3.
The Rainfall layer contains data of rainfall (mm), runoff coefficient (Pcoff) and effective rainfall (Peff) for each distributed point, hence the field of the column for each category was prepared and linked with the attribute table of the rainfall layer. The Rainfall layer contains the rainfall field where rainfall data are stored, the Pcoff field to store the rainfall coefficient to be used for that station and the Peff field to store effective rainfall data. Similarly the field layer contains data of fields Tmax, Tmin, RHmax, RHmin, z, v, n, Lat, h, j, ETo, ETc for weather parameter input for computation of the reference evapotranspiration. Fields named Kc and ETc are also added to store crop factor data and crop evapotranspiration data.
Processing and interface setup
The interactive tool developed within ArcGIS is used for the data input, processing of the data and developing the output thematic maps. Computations required in determining evapotranspiration and irrigation parameters are integrated within the interactive tool triggered by command buttons supported by respective codes. Setup of the interface primarily consists of input of the required data, selection of the relevant data from the list and process for the thematic map. The process also requires selection of the appropriate method of computation for reference evapotranspiration from the list provided in the interface, selection of crop data, soil data from list and processing. A flowchart of the interface setup and data processing is presented in Figure 3.
Generation of thematic map
Spatial information is crucial for efficient irrigation management. In this study, daily weather data for December 2013 were selected to animate maps containing basic control functions to display the maps in an interactive manner. To fulfill the requirement of animated maps pertaining to weather parameters, evapotranspiration and irrigation requirements were created. The user can store and access the created maps as and when needed.
The computed values of ETc and ETo data for each polygon field are used to generate a thematic raster map of reference evapotranspiration and crop evapotranspiration. For interpolation, the raster IDW interpolation technique was employed. The VBA code attached to the raster map of the Reference ET and Crop ET module of the interface tool helps in generating thematic maps of the effective rainfall.
The irrigation requirement thematic raster map is generated using the irrigation requirement module in the interface tool. The module uses thematic raster maps of effective rainfall and crop evapotranspiration. A subtraction cell-by-cell technique is used to generate the irrigation requirement map. The VBA code attached to the irrigation management module of the interface tool allows the generation of a thematic map of irrigation requirement.
Generation of thematic maps using interface
The interface was used for generation of thematic maps for the selected study area with the selected weather, soil and crop data. Daily weather data from Global Weather Data for SWAT (http://globalweather.tamu.edu/) was used for the rainfall and weather data to be processed by the interface and simulate the irrigation requirement. The interface processed these data for simulation of irrigation requirement with the study area.
Generation of rainfall map and effective rainfall map
Generation of reference evapotranspiration map (ETo)
Generation of crop evapotranspiration map (ETc)
The crop ET module in the interface was given as input with a spring wheat crop. The crop coefficient and crop stage data for standard climate conditions were automatically loaded from the interface data. Local climate correction was applied with the weather data automatically loaded from the interface for the field layer. The layer of cropped field was used for processing to generate the daily crop evapotranspiration map (Figure 12).
Generation of net irrigation requirement map
Thus, this tool can be used to generate raster maps of irrigation requirement parameters and is intended for use by irrigation authorities and irrigation management consortia to analyze water requirements and to make easy and quick decisions. The interface tool consists of a graphical user interface, capable of real-time simulation, and is user friendly. The developed interface is prompt in decision-making and capable of spatial irrigation management. Spatial maps can provide information more effectively. The developed spatial maps can be easily interpreted by farmers, planners and specialists for spatial irrigation management.
SUMMARY AND CONCLUSION
The study demonstrated the development and application of a GIS based graphical user interface for irrigation management (GUIIM) within an ArcGIS customization using VBA for simulation of spatial irrigation water requirements. The developed interface tool was successfully employed for Lakhnauta Minor of the Sidholi Distributary of the UGC system of Uttarakhand State, India, to generate spatial thematic maps pertaining to irrigation water requirements including reference evapotranspiration, crop evapotranspiration, rainfall and effective rainfall maps with weather, crop and soil data as input. The GUIIM and generated maps can be helpful in information sharing and visualization for irrigation experts and farmers in irrigation management. The developed interface can be used by irrigation experts for generating thematic maps and further effective irrigation management regarding irrigation allocation and scheduling. Thus, ArcGIS can be customized effectively using VBA to develop a tool capable of simulating spatial irrigation water requirements, which is useful in the decision-making process in irrigation management. This interface tool can be effectively used for any command area to generate thematic maps pertaining to irrigation water requirements.