Impacts of climate change on river hydrology and energy economics in Budhigandaki river basin
Date
2022
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Faculty of Hydrology and Metrology
Abstract
Water management has become a challenging task due to the increasing population,
rapid urbanization and industrialization. Availability of observed hydro-meteorological
data plays a crucial role in water budgeting for the country like Nepal that relies heavily
on hydroelectricity for its energy needs. Quantification of available water at the local
scale and examining how it is impacted by climate change (CC) is extremely important
from the water management perspective at the river basin level. Budhigandaki River
Basin (BRB) of Nepal, was chosen for this study in assessing climate change impact on
river hydrology utilizing well calibrated and validated Soil Water Assessment Tool
(SWAT), consequent impact on hydroelectric energy generation. Extending this aspect
further, the micro-economic assessment of the Budhigandaki hydroelectric project was
also made in this study.
This study assessed the interannual variability of hydroclimatic condition of the BRB
using daily hydrological and meteorological data for the period from 1983 to 2012. To
evaluate the impact of climate change on hydrological phenomenon in the study basin,
future climate data under two Representative Concentration Pathways (RCP 4.5 and
RCP 8.5) with four climatic conditions (cold-wet, warm-wet, warm-dry and cold-dry)
for each RCP were considered. Digital elevation model (DEM) data, land use and land
cover, and soil data of the basin are the spatial data required in the hydrological
simulation that were utilized. The climate change impact on flow, hydroelectric energy
generation and energy economics were evaluated by comparing these variables with the
baseline.
Historical data shows that there is a very high variability in daily, monthly, seasonal
and interannual flow in the study basin. Future annual precipitation in BRB varies
significantly and is projected from -9% to 23% for RCP 4.5 and -11% to 21% for RCP
8.5 scenarios compared to the baseline value (1530 mm). The mean annual temperature
increases 1.7
o
C for RCP 4.5 and 3.9
o
C for RCP 8.5 by the end of this century. SWAT
model was calibrated and validated at Arughat gauging station considering 30 years
daily flow data. Model evaluation using four statistical parameters (NSE, PBIAS, RSR
and KGE) showed that the developed model performed very well to simulate river flow.
Additional validation of the model done at three supplementary points; two in the
upstream and one in the downstream of calibration point (Arughat) also showed that
vi
the developed SWAT model for BRB is well calibrated. To compare the performance
of flow simulation methods in the basin level, a new evaluation statistical index, the
Global Performance Index (GPI), was introduced in this study. SWAT hydrological
model preformed the best among the different methods considered for flow estimation
as evaluated by GPI in BRB.
Annual mean flows are projected to increase in the future scenarios; 10 to 31% in RCP
4.5 and 5 to 57% in RCP 8.5 scenarios with respect to the baseline flow of 240 m
/s.
The analysis of future extreme flow shows an increasing trend in case of annual
maximum one-day flow and a decreasing trend in low flow case. These results indicate
a need to alter the design of hydraulic structures and selection of storage project over
runoff-river project for climate resilience. Future annual energy of the Budhigandaki
Hydroelectric Project is expected to increase by 9 to 13% compared to the baseline
value (3385 GWh) that is equivalent to annual revenue of 20 to 28 million USD.
Results of this study show that storage hydroelectric projects with the provision of
flexible operating rules are desirable. Financial policies related to hydroelectricity need
to be revised with the changes in the future climatic conditions. The findings of this
study are expected to be useful for hydrologists, economists and decision-makers to
plan the use of available water judiciously in the future.
Keywords: Climate change, river hydrology, hydroelectricity, energy economics, GPI,
SWAT, Budhigandaki
Description
Keywords
Climate change, River hydrology, Hydroelectricity, Energy economics