The Western Ghats play a critical role in capturing moisture during the southwest monsoons over the Indian summer. However, their varied topography creates unique orographic effects within the mountain range, which in turn drives vegetation patterns.
We have two heavily instrumented catchments, one in the Aghnashini basin and the other in the Upper Bhavani catchment in the Nilgiris. These catchments provide us unique, long-term data (since 2012) on rainfall intensities, duration and discharge, across the different land cover and land use patterns in the two sites.
The Aghnashini river is one of the few undammed west flowing rivers in South India and it is characterized by a mix of natural evergreen forests, degraded secondary forests, commercial plantations and agricultural fields within human settlements. Whereas, the Upper Bhavani river is highly managed and is an important source of freshwater for hydroelectricity generation, wildlife and other human needs. The instrumented catchment in the Nilgiri basin is devoid of human settlements. However, the natural grasslands that occur in the landscape have witnessed historical modifications with the introduction of non-native invasive species which negatively impacts stream flows, especially during the dry season when demand for water is high.
Our work so far has lead to some key research and data outputs, methodological breakthroughs and establishment of long-term monitoring sites and enhancing capacity in civil society.
The objectives of this grant are to continue monitoring these two sites and to develop new tools and methods in the field of ecohydrology which can be shared with other researchers and civil society.
While we awaited long term funds this project helped us continues our ongoing research in these two catchments and also to facilitate in building capacities of organisations and individuals who are interested in the field of ecohydrology. During the project period both sites were regularly monitored and maintained to collect high resolution data on rainfall and stream-flows.
Along with our field activities we also analysed the relationship between stream flow and daily rainfall across different vegetation types vegetation type. This relationship was further refined to understand how streams under different land-cover types respond to extreme rainfall events. Our preliminary result from the Nilgiri’s indicate that natural forests and grasslands were more efficient in retaining rain water compared to catchments dominated by exotic invasive tree species during extreme rainfall events. For further analysis, we will include other catchment physical properties as catchment morphometry is found to influence stream flows to understand the hydrological responses to such extreme events as this is also important for developing better flood prediction models.
An extreme rain event during the monsoon of 2019 caused extensive damage to the stream gauges installed at the Upper Bhavani site. Nearly two metres of rainfall was received in two days. The deluge resulted in streams overflowing their banks and series of landslides which washed away all but two of our stream gauges. We are presently re-installing stream discharge measuring equipment in the site. Given that virtually all the gauges need replacement, we are using the opportunity to upgrade the instruments and constructing weirs across the newly formed channels. This will allow more accurate monitoring of discharge with a higher degree of automation and lower operation and maintenance costs
