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Mesoscale Water Balance Components Variability Assessment Under The Changing Role Of Temperature And Precipitation Over Snow-glaciers Induced Teesta River Catchment, Sikkim Himalayas, India

Congress: 2015
Author(s): Vishal Singh, Manish Kumar Goyal
Civil Engineering Department, Indian Institute of Technology Guwahati, Assam, India1

Keyword(s): Sub-theme 3: Hydrology,
Abstract

Vishal Singh (Corresponding Author), Department of Civil Engineering, Indian Institute of Technology Guwahati, Guwahati-781039, India Contact No. +918011034682 Email -- vishal.singh@iitg.ernet.in Tel: +91-801103468

Manish Kumar Goyal (Co-Author), Department of Civil Engineering, Indian Institute of Technology Guwahati, Guwahati-781039, India Email - mkgoyal@iitg.ernet.in Tel: +91-361-2583328 Fax: +91-361-2582440

Introduction

In the assessment of streamflow and sub-watershed scale contribution of water balance components (e.g. streamflow) have vital importance in the hydrology. This uncertainty is also aggravated in snow-dominated catchments because of larger interaction among snowmelt and hydrologic processes. This study presents an assessment of the impacts of increasing temperature phenomenon on a series of climate indicators of hydrological regimes across the Himalayan catchment, using a distributed hydrological model SWAT (soil water assessment tool) with climate scenarios constructed using CMIP5 climate ensembles including RCP2.6, RCP4.5, RCP8.5 and AMIP (Fifth Generation Atmospheric General Circulation Model) climate model. Prior studies have focused on macro-scale approaches. Therefore, this study is investigated and evaluated based on the various hydrological components at sub-watershed scale in a glacier and snowmelt induced Teesta river catchment, Sikkim Himalayas, India. The main aim of this study is to assess the water balance components variability in terms of increasing temperature phenomenon on the resultant water balance components through detailed simulation and optimization of the watershed parameters. The existed variability among the water balance components and watershed parameters are identified through the generation of long tern time series present and future hydrological scenarios on a spatial scale at sub-catchment level.

Methods/Materials

This whole study has been divided into three sections: (1) climate downscaling and time series analysis of the temperature and precipitation using CMIP5 based multiple climate ensembles, (2) generation physical data inputs (e.g. landuse/landcover map, soil map, digital elevation model) and preparation of other hydro-meteorological variables (daily temperature, daily precipitation etc.) to setup the SWAT model for simulation of water balance components at sub-catchment scale and (3) forecasting of future water balance components using CMIP5 based multiple climate ensembles. The hydrological model uncertainty is also explored using globally accepted sequential uncertainty domain parameter fitting (SUFI2) algorithm with special integration of SWAT model. The advantage of this approach is that it accounts various sources of uncertainties such as uncertainty in driving variables (e.g. rainfall, runoff), conceptual model, parameters and measured data in special context of various objective functions. The objective functions viz. P-factor, r-factor and coefficient of determination (R2) will be utilized for checking the model strength through model calibration and validation using observed times series data sets.

Result and Discussion

This work is under process. The downscaling part of this current study has been completed. Though, the hydrological modeling of detailed water balance components are still due to be completed. We have divided this study into two time duration based on the observed data sets availability (1979-2005) and future forecasting using CMIP5 based climate ensembles (2006-2100). Based on the time series analysis, we interpret our results to mean that main climate driven factor such as temperature is significantly increased during the past years and upcoming years and has shown large variability across the sub-catchments. The precipitation trends based on the observed data sets and model forecasted data sets have shown significant variability even at sub-catchment level. This notified variability among the temperature and precipitation may indeed alter the water balance during the near-term as well as in the long term futuristic scenarios. However, the magnitude of changes depends upon location specific conditions of the catchment. We also noticed that these changes were mostly happened on the high elevative parts of the catchment.

Conclusion

The major practical advantage of this study is to enhance the understating of snow glaciated catchment components on sub-watershed scale for water resource requirements by formulating locally relevant policies. The current approach together with the multi-objective functions based on parametric estimation may be replicated across other basins to determine relevant requirements and strategies. In this study, various hydrological and meteorological parameters have been considered and evaluated to quantify the precipitation, snowpack, snowmelt and water yield contribution at different parts of the watershed. A sequential uncertainty parameter fitting approach is applied for SWAT model parameterization, sensitivity and uncertainty analysis. SUFI2 approach has provided a supplementary scope of the study. It helps to understand various model calibration parameters with associated uncertainty under changing role of temperature and precipitation, especially at sub-catchment level. The SWAT model demonstrated a significant scope in the current study is of Satluj basin, as using three objective functions viz. p-factor, r-factor and R2 for model calibration and two functions (viz. t-stat and P-value measurement) for sensitivity analysis.
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