Regional water balance analysis of glacierised river basins in the north-eastern Himalaya applying the J2000 hydrological model

The glacierised basins of the Northeast Himalayan region are highly vulnerable to climate-change impacts. The spatio-temporal hydroclimatic and physiographic variability impact the water balance of these glacierised basins across the region. This study assesses the glaciohydrological processes and dynamics in the data scarce region for the present as well future climate change scenarios by regional water balance analysis. The J2000 hydrological model was adapted to incorporate the frozen ground as well as glacier dynamics in a stepwise, nested basin calibration approach. The modelled ERA-Interim precipitation data cannot capture the high amplitude orographic and convective events. Therefore, Orographic correction factors were used to inversely correct the ERA-Interim precipitation data to account for the orographic as well as cyclonic precipitation in the region from reported glacier mass balance and evapotranspiration estimates. Monthly temperature lapse rate was adopted for correcting the ERA-Interim temperature dataset. The Beki basin was selected as the donor basin for model development and evaluation. The parameters from the Beki basin were regionalised to the receptor Lohit and the Noadihing basins by the Proxy-basin method. Multi-objective optimization criteria such as the Kling-Gupta efficiency (KGE) for temporal dynamics and flow distribution and Bias for overall water balance showed high to moderate conformity between measured and simulated discharge at the corresponding basin outlets. The variability in the water balance and runoff components among the three basins was primarily related to the spatio-temporal variation in the mean annual precipitation, runoff and evapotranspiration estimates. The impact of climate-change scenarios on the study basins indicated that water availability would sustain until the end of the century due to higher projected precipitation even though after the depletion of glaciers in the region

DYE-TRACING METHODOLOGY FOR SOIL INFILTRATION ESTIMATION IN GUWAHATI CITY

Soil hydrologic condition is the result of interplay between soil and vegetation which to a great extent govern the infiltration capacity of the soil and hence generation of runoff. Rapid urbanization has significantly increased the risk of flash floods particularly in steep, hilly terrains of Guwahati city especially during high intensity - short duration rainfall events causing large-scale devastations to life and infrastructure. The objective of this paper is to estimate the soil infiltration depth and hydrophobicity useful for hydrological modeling of flash floods.  The results illustrated that vegetative classes like bamboo, forests, plantation or shrubs favour deep infiltration through preferential pathways in the soils. However, homestead or residential areas have showed lesser depth of infiltration due to compressed and impervious areas.  Vegetative classes like forest, plantation, bamboo and shrub classes have showed lesser hydrophobicity than homestead and residential classes. Therefore, Plantation and afforestation on the hills can also help reduce flash floods considerably in Guwahat city. Application of vetiver grass could also effectively detain runoff by conducting runoff to deeper subsurface as they have long, bushy root structure. Therefore dye-tracing is an effective methodology to measure infiltration depths under different landuse classes