Abstract:
In the cold regions because of harsh climates, there exists no or an inadequate number of
monitoring stations. It is indeed a challenge to generate the hydrographs of ungauged basins
with scanty information from limited gauged basins. As a result, it has important implications
for existing water resources systems as well as for future water resources planning and
management since high elevation mountains are all important sources of water to the billions
in the lowlands in these climatic regions.
The Mo Chhu and Po Chhu catchments in Bhutan are used in this study to assess the
regionalization of hydrological model parameters from one catchment to the other
neighbouring catchment having similar characteristics using ABCD hydrological model
incorporating snowmelt parameter. The Mo Chhu catchment was considered as the gauged
catchment and its hydrological parameters were simulated through model calibration and
validation, and then transferred to the neighbouring Pho Chhu catchment. For the
corresponding watersheds, precipitation, streamflow and temperature daily data were collected
for the 11 years from 2006~2017 from the National Centre for Hydrology and Meteorology in
Bhutan and checked by visual comparison, single and double mass curve analysis and annual
water balance to ensure data reliability, consistency and to identify suitable data periods for
model calibration and validation. For the model performance evaluation, Root Mean Square
Error (RMSE), Pearson correlation coefficient (r) and Coefficient of determination (R2) were
used as the objective functions. The Pearson correlation values for calibration and validation
of Mo Chhu basin are 0.84 and 0.88, respectively. When the same model parameters were
transferred to Pho Chhu basin, Pearson value for validation was found to be 0.82, indicating
good inter-basin parameter transferability and effective model regionalization.
Comparing and analyzing the results of ABCD model with and without snow parameter "m",
it can be concluded that the model with snow parameter performs better due to proper
simulation of the major contribution to basin flow from snowmelt. Approximately, over 52%
of the basin flows can be attributed to snowmelt during summer and spring and the
incorporation of snow processes in the monthly ABCD model has thus significantly improved
model performance in snow-covered areas in Bhutan