Papers by Rakesh Kayastha
Journal of Glaciology, 2020
Climate-induced cryospheric changes can have a significant impact on the downstream water availab... more Climate-induced cryospheric changes can have a significant impact on the downstream water availability. In this study, the Open Global Glacier Model (OGGM) and the Glacio-hydrological Degree-day Model (GDM) are integrated to project the response of cryospheric and hydrological systems to climate change until 2100. The study area comprises six sub-basins of glacierized Koshi River basin covering Nepalese and Chinese territories. The output from OGGM is provided as input to GDM along with the spatial and hydro-meteorological data. The average glacier area change in all the sub-basins from 2021 to 2100 is estimated as 65 and 85% decrease and the average glacier volume change is estimated as 76 and 86% decrease for RCP 4.5 and 8.5 scenarios, respectively. The future simulated discharge shows an increasing trend in pre-monsoon and monsoon seasons and a decreasing trend in post-monsoon and winter seasons after 2060 in all the sub-basins, which can lead to wetter wet seasons and drier dry ...
Frontiers Earth Science, 2020
An assessment of the water supply and its seasonal and annual changes over the century in the Hig... more An assessment of the water supply and its seasonal and annual changes over the century in the High Mountain Asia (HMA) region is of increasing interest due to its potential impact on one-sixth of the global population. In order to understand the changing hydrology and snow and ice melt, we used remotely sensed Advanced Scatterometer (ASCAT) observations of glacier melt (GM) and a distributed and gridded Glacio-hydrological Degree-day Model (GDM) in three river basins: Tamor, Trishuli and Marsyangdi. The GDM-estimated contribution of snowmelt, icemelt, rainfall and baseflow in river flows is found to be most accurate in the Trishuli River basin, with Nash-Sutcliffe efficiency (NSE) between the estimated and observed discharges of 0.81 and volume differences of −0.5%, and reasonably accurate in the Tamor River basin, with NSE of 0.69 and volume difference of −7.51%. Similarly, NSE of 0.81 and volume difference of 4.64% in Marsyangdi River basin. We find strong similarities in the timing of glacier melting using the GDM and from observations from the ASCAT GM, determining the seasonal start of glacier melting to within 6 days on average. In all basins ASCAT GM observes melting at higher elevations relative to GDM, average of 5,328 m a.s.l. Systematic differences in glacier melting area determined by modeling and satellite observations indicate ASCAT may have suboptimal resolution, view geometry and/or polarimetry for delineating glacier melting at the process-scale in complex topography, especially in the ablation zone. This is the first step in examining the remote sensing products that could potentially be incorporated into hydrologic models to increase the accuracy of the hydrologic flow as well as the ability to estimate river discharge in other basins with limited data.
Glacio-Hydrological Degree-Day Model (GDM) Useful for the Himalayan River Basins
Dimri A., Bookhagen B., Stoffel M., Yasunari T. (eds) Himalayan Weather and Climate and their Impact on the Environment. Springer, 2020
This chapter describes a Glacio-hydrological Degree-day Model (GDM)
which uses degree-day factors... more This chapter describes a Glacio-hydrological Degree-day Model (GDM)
which uses degree-day factors for estimating snow and ice melt that calculates total discharge from a river. It is a physically based gridded glacio- hydrological model which is useful for the Himalayan river basins. The GDM is successfully used in the Marsyangdi River basin (MRB) and Trishuli River basin (TRB). The model is first calibrated and validated by using observed discharge over the period of 2004–2014. A long-term continuous simulation is then carried out for 2020–2100 in both basins. Results show that the model simulations are good. The Nash-Sutcliffe Efficiency (NSE) are 0.79 and 0.83 for the period of 2004–2007 in MRB and from 2007 to 2010 in TRB, respectively during the calibration period and 0.81 and 0.76, for the period of 2008–2010 in MRB and from 2011 to 2014 in TRB, respectively. The snow melt and ice melt contributions to total discharge in MRB are 15% and 13%, respectively whereas 12% and 16% in TRB for the calibration period. The Representative Concentration Pathways (RCPs) 4.5 W m−2 scenario for the period of 2020–2100 shows an average increase of simulated discharge by 1.43 m3 s−1 per year and 0.25 m3 s−1 per year for MRB and TRB, respectively. Similarly, in RCP 8.5 the discharge increases by 0.71 m3/s per year and 0.94 m3 s−1 per year in MRB and TRB, respectively. The model can be used as a promising tool for the study of hydrological system dynamics and potential impacts of climate change on the Himalayan river basins.
which uses degree-day factors for estimating snow and ice melt that calculates total discharge from a river. It is a physically based gridded glacio- hydrological model which is useful for the Himalayan river basins. The GDM is successfully used in the Marsyangdi River basin (MRB) and Trishuli River basin (TRB). The model is first calibrated and validated by using observed discharge over the period of 2004–2014. A long-term continuous simulation is then carried out for 2020–2100 in both basins. Results show that the model simulations are good. The Nash-Sutcliffe Efficiency (NSE) are 0.79 and 0.83 for the period of 2004–2007 in MRB and from 2007 to 2010 in TRB, respectively during the calibration period and 0.81 and 0.76, for the period of 2008–2010 in MRB and from 2011 to 2014 in TRB, respectively. The snow melt and ice melt contributions to total discharge in MRB are 15% and 13%, respectively whereas 12% and 16% in TRB for the calibration period. The Representative Concentration Pathways (RCPs) 4.5 W m−2 scenario for the period of 2020–2100 shows an average increase of simulated discharge by 1.43 m3 s−1 per year and 0.25 m3 s−1 per year for MRB and TRB, respectively. Similarly, in RCP 8.5 the discharge increases by 0.71 m3/s per year and 0.94 m3 s−1 per year in MRB and TRB, respectively. The model can be used as a promising tool for the study of hydrological system dynamics and potential impacts of climate change on the Himalayan river basins.
Journal of Glaciology, 2020
Climate-induced cryospheric changes can have a significant impact on the downstream water
availab... more Climate-induced cryospheric changes can have a significant impact on the downstream water
availability. In this study, the Open Global Glacier Model (OGGM) and the Glacio-hydrological
Degree-day Model (GDM) are integrated to project the response of cryospheric and hydrological
systems to climate change until 2100. The study area comprises six sub-basins of glacierized
Koshi River basin covering Nepalese and Chinese territories. The output from OGGM is provided
as input to GDM along with the spatial and hydro-meteorological data. The average glacier
area change in all the sub-basins from 2021 to 2100 is estimated as 65 and 85% decrease and the
average glacier volume change is estimated as 76 and 86% decrease for RCP 4.5 and 8.5 scenarios,
respectively. The future simulated discharge shows an increasing trend in pre-monsoon and
monsoon seasons and a decreasing trend in post-monsoon and winter seasons after 2060 in
all the sub-basins, which can lead to wetter wet seasons and drier dry seasons in the far future.
A shift in peak flow is observed from August to July in most of the sub-basins. The coupled modelling
technique used in this study can largely improve our understanding of glacio-hydrological
dynamics in the Himalayan region.
availability. In this study, the Open Global Glacier Model (OGGM) and the Glacio-hydrological
Degree-day Model (GDM) are integrated to project the response of cryospheric and hydrological
systems to climate change until 2100. The study area comprises six sub-basins of glacierized
Koshi River basin covering Nepalese and Chinese territories. The output from OGGM is provided
as input to GDM along with the spatial and hydro-meteorological data. The average glacier
area change in all the sub-basins from 2021 to 2100 is estimated as 65 and 85% decrease and the
average glacier volume change is estimated as 76 and 86% decrease for RCP 4.5 and 8.5 scenarios,
respectively. The future simulated discharge shows an increasing trend in pre-monsoon and
monsoon seasons and a decreasing trend in post-monsoon and winter seasons after 2060 in
all the sub-basins, which can lead to wetter wet seasons and drier dry seasons in the far future.
A shift in peak flow is observed from August to July in most of the sub-basins. The coupled modelling
technique used in this study can largely improve our understanding of glacio-hydrological
dynamics in the Himalayan region.