Understanding Hydrological Processes of Himalayan Hillslopes (PI: Prof. Sumit Sen)

Regional mountain ecosystem is completely affected by changing pattern of temperature and rainfall in the Himalayan region. The Himalayan climate that affects the climate of the entire Asian continent, landscape, and biodiversity is unique on its own. In a Himalayan ecosystem, climatic variables change frequently over a very short distance which affects its hydrological processes like precipitation, runoff and erosion . The geologically and ecologically diverse Lesser Himalayan terrain is highly prone to natural disasters such as forest degradation, soil erosion, landslides and floods during extreme rainfall events. At this alarming situation, hydrology of this non-linear and dynamic region needs to be studied by hydrologists to understand heterogeneous hydrological processes like the runoff generation mechanism, runoff pathways, interaction of vegetation with surface runoff and subsurface flow behavior.  

The main aim of this study is to create a hillslope-scale dataset in Lesser Himalayan Region to understand the interactions among different hydrological, meteorological and topographical components. An ungauged experimental watershed i.e. Aglar watershed was selected to carry out this hillslope-scale hydrological processes understanding research by analyzing the following specific objectives:

1. Understanding the plot-scale hydrological processes using HYDRUS-2D overland flow module under artificial rainfall condition. 
2. Exploring the hillslope-scale hydrological connectivity using spatiotemporal variation of soil moisture and its correlation with the topographic wetness index (TWI) and soil hydraulic conductivity.  
3. Estimating the thresholds controlling hillslope runoff processes in infiltration-excess dominated flow landscape and develop the relationship between soil moisture and runoff generation using the concepts of complex network theory.
4. Understanding the linkage between the soil moisture and soil temperature during different rainfall intensity and duration.

In this study, we investigated runoff generation thresholds and the spatial analysis of soil moisture matrices, i.e., wetting front velocities and initial response time in three different Mediterranean catchments of the Southern Sierra Nevada region. We are answering the following research question in this study: (i) How the soil moisture and rainfall influence the runoff thresholds in Mediterranean headwater catchments? (ii) Is there any spatial variability in runoff thresholds within a catchment? (iii) How do soil moisture indices and preferential flow occurrence vary spatially and temporally? 

(iv) Seasonal and spatial variations of soil moisture and discharge hysteresis and its governing factors