Developing a “Centre of Excellence for Hydrologic Modeling” and giving leadership to the Country in hydrologic modelling services is one of the four major tasks assigned to NIH under the NHP. To grow and sustainan, the centre has to become knowledge repositories in hydrological processes understanding, advanced tools and techniques, advancement taking place from time-to time globally on hydrological research, tools and techniques to respond to the India's hydrologic modelling services. To attain this objective, the Institute has to have capabilities and resources to develop demand driven tools and techniques using popular computational platforms and help capacity building of the Country through technology and knowledge disseminations. The aim is to make India self reliante in water management tools and techniques to help decision making on movement, availability, fate and quantity and quality management of both surface and sub-surface water. The 'Centre of Excellence' will primarily deal with three components: Surface water Modeling; Groundwater Modeling; and Water Quality Modeling. Web-enabled models and e-learning packages on hydrological modules will be developed.

CONEPT NOTE Centre of Excellence for Hydrologic Modeling (CoEHM) at National Institute of Hydrology, Rorrkee

To become self-reliant by  developing, strengthening and excelling on various fronts of “Hydrologic Modelling” activities and cater hydrologic modelling services to the country as knowledge repositoriescentre on various facets of hydrology, advanced tools and techniques,and dissemination of those by continuing education and training to differentimplementing agencies of NHP and other professionals.

A “Hydrological Modelling” unit would be considered a “Centre of Excellence”, if it possesses the following characteristics:

• Has competence to act as  knowledge repositories for hydrologic modelling,
• Has aspiration to develop  hydrological models and modelling tools,
• Has ability to give quick responses to queries from  state and central agencies, stakeholders, and other aspirants,
• Has desire to adopt advanced  knowledge on models&modeling tools,
• Has good International & National network and cooperation for updating advanced knowledge  on modelling and for accessing global best practices,
• Has ability to take forward continuing education & knowledge dissemination activities,
• Has expertise to develop simplified hydrological modules for quick assessment & computation,
• Has dedicated team for developing  software and modeling tools,
• Has facilities of advanced hardware and software , etc.  

Over the passage of time, mainly in last three decades, with the advancement of computational facilities, data acquisition, interpretation and integration technologies, and better process understanding, a numerous hydrological models based on stochastic, deterministic(lumped, semi-distributed & distributed), and process description (empirical, conceptual and physical) approaches covering surface water, groundwater and water quality were developed worldwide and successfully applied for solving real life problems of various dimensions and categories. Most of those hydrological models were developed by professionals from the developed countries, which have long standing onscientific data acquisition systems andadvanced skills. Capabilities and potentiality of the developed models for simulating thehydrological responses,for which they were developed, were also demonstrated for solving wide range of problems using databases as depicted in the models. Most of the models developed have their own merits, limitations, data requirement and complexities in use.A model suitable for a particular case analysis has limitation to describe the results effectivelyto some other hydrological problems. A number of conceptualized generic models based on different approaches or by employing numerical schemes on governing equations of the respective hydrological processes were also developed and put into the public domain for wide range of applications. Some of those process based generic models have received worldwide acceptability and are popularly used. 
The advancement of satellite based digital data acquisition systems and RS & GIS techniques as data management tools, some of the widely used conceptualized generic models are promoted as commercial products by a number of International professional organizations either as standalone model or by integration to one-another with  user friendly interfaces. These commercial products have gained or are gaining popularity in many countries including India, because of increasing hydrological problems driven by population dynamics and economic development, user friendly data handling and graphical interfaces, good promotional and marketing strategy, etc.Successful applications of all those models in Indian hydrological contexts are not guaranteed unless conditions based on which theyhad been derived are satisfied. Albeit the commercial models are mostly generic in nature,supported by user friendly integrated interfaces, and have promising potential for successful applications but they are priced and require specialized training for successful use. Rely on commercial models aiming to customized, time to time up-gradation and continuous skill development may not be a logical proposition to attain self sufficiency in hydrological modelling for country like India that has excellent expertise on hydrological modelling knowledge. We need to develop our own skill for becoming self reliant on developing indigenous framework of integrated models and to provide sustaining modelling services.There are number of open source models, which have wide acceptability worldwide, but lack in user friendly integrated interfaces and rigorous testing in Indian hydrological conditions. The promising open source models together with hydrological modules developed and tested using Indian hydrological data can be integrated with advanced data management tools by developing appropriate interfaces to make them users friendly.
A great deal of success on hydrological modelling in India is evident from academia and research organizations.Numerous published scientific papers and study reports from researches in India revealed, successful applications of some promising hydrological models in Indian context and development of own source codes and their successful field applications. However, most of the tested source codes remained in the backbench due to lack in professional approaches for making  those source codes user friendly in the data management, graphical interfaces and promotional activity. The promising part of those developed source codes and models are;they had been indigenously developed to suit Indian hydrological conditions and tested with available hydrological data. The indigenously developed models and their computational capabilities in simulating hydrological responses could give a better standing than using rigorous data driven models promoted commercially.
Hydrological models are developed to solve field problems and help faster decision making in resource management and forecasting natural extremes events, etc. Therefore, the beneficiaries of any developed hydrological models are the professionals, who use those models to resolve some questions. Thecommon concerns among readymade model users in India are: which model is the best for what purposes, how to calibrate a model, what data ranges are required for calibration and validation, how to select a model for correct scenarios analysis, etc. Reasons of such concern may be due to lack of understanding, skills and knowledge on limitations in the application of hydrological models. The success and fate of a hydrological model depend on the skill of the person using the tool and the databases one has for the modelling. Nevertheless, the successful application of hydrological models and modelling approaches mostly found giving unexpected results or not satisfactory outputs due to lack of appropriate data library and adequate data. These can be made possible to counteract when the system is adequately understood and conceptualized with good databases and the personsusing the model have sufficient knowledge on modelling. Modelling is not just entering data into existing modelling packages and reporting the results; a garbage in can bring a garbage out. Modelling requires thorough understanding of the system to refine the conceptualized elements to maximize knowledge about current state of a hydrological behaviour and the possible future impacts of proposed development.
Sustainable development and management of water in the context of emerging climate change impacts in addition to the other hydrological issues pose major challenges for spatiotemporal assessment and auditing of water availability, both on local and regional scale, and scenario analysis of water systems behaviour due to various hydrological interventions and natural stresses. These can eventually be achieved by integrated modelling approaches using models, which are compatible to hydrological conditions, data availability and users in India; and whose characteristics and behaviours are well understood for deriving the uncertainty and inconsistency.
Scientific understanding of hydrological systems, data gathering, monitoring and computational technologies in India are rapidly expanding. These advancements many ways simplify the modelling tasks easy, less time consuming and help in taking quick decision. However, for identifying, suggesting and integrating the best suited models for integrated modelling approaches for varying hydrological and hydro-geological conditions, there is a need to full-scale application and testing of most promising open access and commercial hydrological models by systematic data collection from select pilot hydrological basins and evaluate the performances of the models emphasising the degree of uncertainty for different levels of data and parameters simplification. Based on the performances evaluation,standardization of the models for different applications would only be possible.To achieve these, there is a need to become self-reliant in hydrological modelling by systematic analyses of various modelsto evolve as knowledgerepositories for catering the continuing education and services on advanced modelling tools, techniques and in capacity building to the field & other water professionals.
Based on the above, the gaps in India are briefly listed below:

• Numerous promising hydrological models covering areas of surface water, groundwater and water quality are available as open source&commercialmodels. The commercial modelsare gaining popularity in India, because: (i) there are no indigenously developed contending models; (ii) they have user friendly data handling, data management and graphical interfaces; (iii) these models havegood promotional and marketing strategy, etc. However, these models are highly priced and require specialized training and time-to-time up-gradation for successful use. There are number of open source models, which have wide acceptability worldover, but lack in user friendly integrated interfaces. The promising open source models need a comprehensive performance analysis in the context of Indian hydrological conditions and data to accept as a part of the integrated hydrological model(s) or to promote as the best suited model(s) for Indian conditions.
• Uses of both commercial and open source models in India depend on access of the models, conveniencesof users, data availability and knowledge on modeling. These uses are found mostly confined in the research areas. Field professionals have limited access to hydrological models owing to lack in understanding, skills require to use the model, knowledge on limitations embedded in the models, etc and also lack of information on the modelsto decide which models are the bestfor what purposes and how to select a model for correct scenarios analysis.
• Lack of standardization and customization of models based on hydrological conditions, data need and results expected, level of uncertainty describes by the model, categorization of models’ parameters, users skills necessary, etc can also be regarded as gaps.
• Hydrological models developed in academia and research organizations in India based on modelling exercises and source codes developed using Indian hydrological data are yet to translate in the form of professional modules in the hydrological models being used in India.
• To suggest which models suit for what data ranges and hydrological conditions and level of uncertainty describes by a model, gap between data requirement by the models and data availability is inevitably common in Indian context. To ascertain efficacy ofa model, there is a need to full-scale application and testing of most promising open access and commercial models by systematic data collection from select pilot hydrological basins and evaluate the performances of the models to ascertain the degree of uncertainty for different levels of data use and parameters simplification.
•  Model(s) good for specific purposes may not give expected results to other hydrological conditions arewell known fact but seldom recognized when applied due to inadequate knowledge about models’ capability and limitations.
• Lack of functional arrangement between the field/implementing organizations and the expert Institutes about sustainable disseminative approach is an important gap.
• Integrated water resources management (IWRM) has emerged as the way forward for sustainable water resources development and management. Therefore, the hydrological models and modeling services should be such that they deal with components of IWRM andare capable to simulate integrated response of components. There is a need to develop /implement “Integrated Hydrological Model(s)” by integrating surface water, groundwater, water quality, vadose zone, snow & glacier and sediment transport components and use the results for planning and management of water resources.

Recognizing the above gaps, the objectives of CoEHM are framed to address the followings:

• Review, identify and select promising open source and licence based widely used hydrological models covering different areas of hydrology and evaluate critically their strength, weaknesses, characteristics, dimensions, I/O requirements, etc for full-scale application;

• Evaluatecomprehensive performancesof the domain models by applying them into same databases obtained from devised systematic data monitoring activitiesof few pilot basins andinter-compare their responses to categorize them as per their performances, data requirements, sensitivity of parameters, andascertain the level of uncertainty of each model,

• Standardize guidelines & procedures for use of various categories of models and prepare a library of parameters’values for different hydrological and hydrogeological conditions and water quality constituents,

• Searchand examine scope to integrate promising hydrological models developed in India and tested with Indian hydrological conditions& data, as added/optional modules in  modelsdecided from (ii) by proper synthesizing,

• Develop web-enabled models for most frequently used hydrologic componentsand share those in public and professional domain. Develop e-learning demonstration and dissemination materials for capacity building of  field professionals,

• Provide hydrological modelling services to the country including Implementing Agencies (IAs) of NHP by continuing education and dissemination of advanced knowledge, tools & techniques,and act as knowledge repositories centre for interacting and guiding in hydrologic modelling activities;

• Build-up network and coordination by cooperation, engagement and exchange programwith National and International organizations/professionals involved in developing hydrological model(s) and explore possibility to associate them in “Make in India Hydrologic Models” program and in dissemination & training activities.

• Finally, bring out prospectivehydrological models, which can be endowed as referenced models for up-gradation and promotion in the Country, and develop a comprehensive decision support system to address“Integrated Hydrologic and Water Resources Management” by integrating the potential hydrologic modules in user-friendly data management tools and platform.

The following methodologies are envisaged to achieve the objectives:

• Prepare status document covering all aspects of hydrologic modelling, viz. surface water modelling that includes rainfall-runoff and flood modelling, snow/glacier melt runoff modelling, water resources systems modelling, and soil erosion and sediment yield modelling; groundwater modelling that includes, flow and contaminant transport; and surface water quality modelling, by reviewing status of the above aspects in India. The review would focus on: (a) issues and challengesin the respective area, (b) gaps, (c) state-of-art techniques/methodologies, (d) models available/developed on different areas, (e) characteristics of models and their scope and limitations,(f) a critical appraisal on available models,(g) improvement /modification/simplification necessary to adopt those in the Indian context, etc.

• The status document would lead to selection of few promising models (open source and commercial model) for their performance evaluation. The detailed insights of the selected models including their mathematical and numerical settings, I/O environment, and data requirement for full-scale implementation would be studied.

• Three representative basinsas pilot cases would be taken up for comprehensive performance evaluation of the selected hydrological models. These representative basins would systematicallybe instrumented and experimented to generate suitable databases including parametric values as required by different models fortheir full-scale application and performance evaluation.

These three representative basins are:

• Upper Yamuna Basin upto Delhi
• Tel Basin in Odisha
• Narmada Basin

• As these three pilot cases would represent specific hydrological issues and problems, therefore, by taking them as special projectsto address a number of purposes could economize time, efforts and money. These purposes are: (a) systematic data collection efforts by setting instrument or observatory to obtain required time-series data for full-scale application of different models, (b) use of those data for giving solutions to  problems of the respective catchment under different hydrological scenarios, and (c) use of data for testing & performance evaluation of different models.

• Based on the performance evaluation, the models shall be categorized and standardized.

• Simultaneously, the exploratory work for studying the insights and capability of hydrological models developed in India shall also be continued.

• Development of user-friendly interfaces of promising models and integration of one module to another shall also proceed simultaneously.

• Education and dissemination activities related to modelling and modelling tools shall also be taken up suitably.

• Web-enabled and e-learning modules shall also be part of continuing efforts.

• To pursue and achieve the envisaged objectives, a great deal of expert knowledge on various aspects of hydrology, modelling skills, mathematical knowledge, software expertise, computer program writing, etc. shall be necessary. The critical and intellectual parts in development of a computer source codeare managing array variables in computation on space-time and managing the matrices in the iterative processes. Navigation of data and results from one module to another and running the computational engines simultaneously. To accomplish these tasks, skilled professionals from India and abroad as per the requirement on various subject matters shall be associated with activities of “CoEHM” by either hiring or outsourcingjob-wise. 

The following outputs are expected from the activities of “CoEHM”:

• A peer-reviewed status document on “Hydrologic Modelling” emphasising current status and future directions. This has been completed and is being publishrd.
• Identified promising hydrological models recommending their features, areas and problems for which suitable for uses, data requirement, etcshall be an important output.
•  Standardize guidelines and procedures for hydrologic modelling.
• Web-enabled models for commonly required hydrologic components estimation.
• Training and dissemination of knowledge, advanced tools and technologies to IAs and other professionals.
• Capacity building of the country on hydrological modelling.
• Shall emerge as a self-reliant centre to cater “Hydrologic Modelling” services to the country.
• A number of promising hydrological models suitable for India shall be fabricated by user friendly interfaces for ease in uses.

Highly complicated and time consuming works are associated with the activities of “Centre of Excellence”. Writing correct source codes and making computer programs full-proof are tedious and time consuming jobs. The works associated with writing a computer program having array variables that deal with 3 Cartesian coordinates and one time domain variable requires good passion, tremendous skills and understanding. Capturing work elements on timeline and maintaining the timeline are difficult. A typical workflow diagram showing major work elements and expected outputs is given in Figure 1.

Figure 1 : Workflow diagram showing major activities of “Centre of Excellence”.