Browsing by Author "Rao, G. Venkata"

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    Evaluation of NCEP-GFS-based Rainfall forecasts over the Nagavali and Vamsadhara basins in India
    Rao, G. Venkata; Reddy, Keesara Venkata; Sridhar, Venkataramana; Srinivasan, Raghavan; Umamahesh, N. V.; Pratap, Deva (Elsevier, 2022-11-01)
    Rainfall forecasting and its spatio-temporal variability is important for many hydrological applications. It is critical to understand the uncertainty and verify the quality of rainfall forecasts provided by Numerical Weather Prediction (NWP) models. In the present study, the National Center for Environmental Prediction (NCEP) Global Forecast System (GFS) model performance is evaluated for day-1 to day-5 forecast with a threshold of 1 mm/day in the Nagavali and Vamsadhara river basins, India. From the results, the model predicted the rainfall with a correlation coefficient of >0.3 and probability of detection >0.6 for day-1 and day-3 forecasts. The bias in rainfall prediction shifted from overestimation to underestimation by 30% as forecast lead time increased. The total mean error is decomposed into hit, false, and missed bias. The main sources of total mean error are hit bias and false bias. However, missed bias influenced total mean error as lead time increased. Bias correction is applied for the rainfall events with a rainfall intensity >12 mm/day. RMSE improved by >18% for day-1 forecast in both the Nagavali and Vamsadhara basins, and the improvement ranged between 3% to 9% for other days. In the Nagavali basin, BIAS and ME improved and ranged from 44% to 65% for day-1 to day-5 forecast, whereas in the Vamsadhara basin, it ranged from 65% to 93%. Our findings are useful for early warning dissemination during the flood events, resource mobilization to protect communities, and sustainable water resources planning and management.
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    Real-Time Flood Forecasting using an Integrated Hydrologic and Hydraulic Model for the Vamsadhara and Nagavali basins, Eastern India
    Rao, G. Venkata; Nagireddy, Nageswara Reddy; Keesara, Venkata Reddy; Sridhar, Venkataramana; Srinivasan, Raghavan; Umamahesh, N. V.; Pratap, Deva (Springer, 2024-02-23)
    Due to recent rainfall extremes and tropical cyclones that form over the Bay of Bengal during the pre- and post-monsoon seasons, the Nagavali and Vamsadhara basins in India experience frequent floods, causing significant loss of human life and damage to agricultural lands and infrastructure. This study provides an integrated hydrologic and hydraulic modeling system that is based on the Soil and Water Assessment Tool model and the 2-Dimensional Hydrological Engineering Centre-River Analysis System, which simulates floods using Global Forecasting System rainfall forecasts with a 48-h lead time. The integrated model was used to simulate the streamflow, flood area extent, and depth for the historical flood events (i.e., 1991–2018) with peak discharges of 1200 m3/s in the Nagavali basin and 1360 m3/s in the Vamsadhara basin. The integrated model predicted flood inundation depths that were in good agreement with observed inundation depths provided by the Central Water Commission. The inundation maps generated by the integrated modeling system with a 48-h lead time for tropical cyclone Titli demonstrated an accuracy of more than 75%. The insights gained from this study will help the public and government agencies make better decisions and deal with floods.
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    Spatio-temporal analysis of rainfall extremes in the flood-prone Nagavali and Vamsadhara Basins in eastern India
    Rao, G. Venkata; Reddy, K. Venkata; Srinivasan, Raghavan; Sridhar, Venkataramana; Umamahesh, N.V.; Pratap, Deva (Elsevier, 2020-05-29)
    Understanding the spatio-temporal distribution of rainfall characteristics has a major role in assessing the availability of water resources over a catchment. Therefore, it is necessary to understand the changes in rainfall characteristics using gridded precipitation data and robust statistical analysis for making decisions. In this study, the trends in rainfall and rainfall extremes over the Nagavali and Vamsadhara river basins are studied at three time steps (long-term-1901-2018, pre-1950, and post-1950) with four different Mann-Kendall (MK) tests using daily gridded rainfall data of 118 years (1901–2018). The spatial patterns of the trends are evaluated with the kriging interpolation method. Magnitude in rainfall and rainfall extremes (CDD, CWD, PRCPTOT, R10MM, R20MM, R40MM, R95PTOT, RX1DAY, and RX5DAY) are analyzed using the Sen’s slope method. Except in the monsoon season, a decreasing trend is observed in all the rainfall extremes in post-1950 compared to pre-1950 period. Whereas, in the monsoon an increasing trend is observed for the extremes in post-1950 period. Overall period (i.e, 1901–2018) an increasing trend is observed for rainfall and rainfall extremes in the pre-monsoon (March–May), monsoon (June–Sep) seasons and a decreasing trend in the winter season (Dec–Feb) for both the basins. No obvious trends are evident in the post-monsoon season (Oct–Nov). At the annual scale, rainfall and rainfall extremes exhibited an increasing trend. Overall, the Nagavali basin experienced more extreme rainfall events indicating the higher vulnerability of floods while the middle and lower portions of the Vamsadhara basin shown increase in extremes. When linked with hydrological analysis, insights gained from this study are useful for flood vulnerability mapping and risk assessment for both the basins.