Dear Dr. Puranadare,
You have raised very valid points for discussion. As these points required inputs from our CWC experts, it took some time to get it.
The replies to your questions are as below:
1. To what extent Distributed & Ensemble Models models are being used in India? Any example & its experience?
a) Distributed models:
Distributed models capture the spatial distribution of input variables like rainfall, temp and physical parameters like land use, soil, elevation etc. The recent study on water availability using spatial inputs for all the basins in Basin planning unit of Central Water Commission are done based on distributed Modelling ( 56m LULC resolution)
http://www.cwc.gov.in/main/downloads/Reassessment%20of%20Water%20Availability%20-Main%20Report.pdf
IIT Delhi used the distributed SWAT model for climate change impact analysis for Ganga basin. Besides, the fully distributed models like SWAT, quasi distributed model like WMS and others are in use in academic institutes and other research institutes.
b) Ensemble models:
The multi-model ensembles are expected to bring out more reliability in the model outputs regarding the future runoff regimes of the basins than that could be brought about using individual models. IMD has the operational forecasts models on short to medium range for various user specific applications like public weather forecasting, agriculture, hydrology, disaster management etc.
Water availability is affected by the anticipated changes in temp, precipitation, atmospheric and oceanic circulations and other climate variables depending on the scenarios. The climate change impact on ET, rainfall, runoff and water availability has been shown to be affected by the uncertainty associated to climate scenarios. An ensemble of hydrological models displaying a range of complexity is used for research in IITM, IMD and NCMRWF. In 2007, a new statistical forecasting system based on the ensemble technique was introduced for the seasonal rainfall forecasting over the country as a whole.
IITM and IMD use the method to improve the accuracy, reliability and range of weather forecasts through the use of ensemble and multi-model ensemble techniques. Besides, National Centre for Medium Range Weather Forecasting, Noida uses global ensemble prediction system of UKMO with 50 ensemble members.
Seasonal and extended Range Prediction group of IITM has been providing experimental real-time forecast of the active-break spells of Indian Summer Monsoon Rainfall since 2011 up to 4 pentad lead using an indigenously developed Ensemble Prediction system based on Climate Forecast System Model. The EPS generates a large number of forecasts from different initial conditions so that the expected forecast and also the expected spreads or uncertainties in terms of probability from this forecast can be informed.
2. What is the mechanism to document changes in basin properties & notify the same? Its periodicity?
Land use changes may have significant impact on erosion and agricultural soil properties, including soil degradation by acidification, leaching and organic matter depletion. Land use pattern is a key factor for landscape planning and development. There is no clear cut mechanism to document changes in basin properties and notify the same. In case there is a distinct change in the land use pattern due to anthropogenic or natural phenomena, the same can be documented in the LULC change. Also, there are no guidelines for periodicity as such. But annual changes are mapped by NRSC, Hyderabad through lULC mapping. NBSS Nagpur maps the soil texture changes through survey periodically.
3. How authenticity & reliability of hydrological data is ensured in practice?
Water resources cannot be managed, unless we know where exactly they are, in what quantity and quality, and how variable they are likely to be in the foreseeable future. The hydrological data must be of authentic and reliable. The data quality required for a specific purpose will depend to a significant degree on the requirements of the application areas and it needs to be recognized that not all data is fit-for purpose in all application areas.
BIS/ISO standards are available in this domain for establishing the gauges, recording the water levels, measuring discharges in the open channels etc. By strictly following the prescribed methods and necessary precautions the reliability and authenticity of the data can be ensured. The hydrological data collection network has to be automated (through advanced types of sensors and telemetry) to avoid systemic & human errors. O & M of this network also has a large impact on the quality & reliability of the data. In CWC, regular inspection of sites are carried out by higher officials (viz. Sub Divisional, EE,SE and CE) and river discharge also observed with additional check current meters to ensure the quality of the data.
In addition to the above, number of statistical tests like Screening, Homogeneity Test, Randomness Test, Consistency Check, Primary and Secondary Validation etc. are applied to validate the correctness of hydrological data and relevant acceptance, rejection or modification are generally applied to the dataset before being used in any hydrologic analysis. Software packages like HYMOS, SPSS or SYSTAT are very useful.
4. Should it not be mandatory to have qualified hydrologists in Water Resources Department to give justice to all matters related to hydrology?
Yes, it is always better to have qualified hydrologists and water resources professionals to deal with planning, design of water resources and WR modeling in particular using domain knowledge providing hydrological inputs.
The very objective of the present course is to create a pool of trained hydrologists across various Organisations; who would have necessary knowledge & skills to give justice to all matters related to hydrology.
Thanks for starting the discussion on the subject.
All the best.
Dattakumar Chaskar