Deodars in HP’s Sangla Valley provide insights into climatic changes that could help form future policies

Deodar trees in Himachal Pradesh’s picturesquare Sangla Valley have revealed the process of climatic shifts from wetter spring conditions that prevailed during pre-historic times to drier conditions from the year 1757 onwards.

A new study has highlighted the critical role of climate variability that is driven by regional and global factors in triggering the geo-hazards, underscoring the need for forest management, sustainable land use, monitoring and early warning systems.

By studying the pattern and characteristics of rings in the trunk of Deodar trees, scientists reconstructed the climatic patterns over the past 463 years and a 168-year rockfall activity in the western Himalayan region. Deodar is native to the Himalayas and is a large evergreen coniferous with needle-like leaves, reaching 40–50 metres in height and widely used for construction and herbal medicine.

Tree-rings, layers of new wood that form each year, provide a record of the tree’s age and past environmental conditions, act as natural archives to such climatic and geo-hazard events. The study analysed the factors responsible for geo-hazard activities, enabling better prediction of future hazard events to support early warning systems.

According to the researchers, the increasing frequency of extreme climatic events, such as droughts and floods, and their strong association with geo-hazards like landslides, glacial lake outburst floods, rockfalls and avalanches, especially in the Himalayan region, underscored the need for robust reconstructions of past hydro-climatic variability and related geo-hazard episodes.

They explored past climate using dating of annual growth layers in trees through dendroclimatology, the science of studying past climates by analysing tree rings, and dendrogeomorphology, the science of using tree rings to date and understand past geological events like landslides, floods and rockfalls.

A total of 53 rockfall events, including eight of high intensity, were linked to dry spring conditions, especially after the year 1960, indicating climate-induced ground instability. The spring drought conditions led to slopes with poor vegetation cover, exposing them to vulnerability when the dry conditions are followed by intense summer monsoon rains.

The study showed that tree growth is highly sensitive to spring moisture, primarily influenced by winter precipitation derived through western disturbances. Undertaken by six experts from the Birbal Sahni Institute of Palaeosciences, Lucknow, Space Applications Centre, Ahmedabad, Friedrich-Alexander University, Germany and Paris Lodron University, Austria, it has been published in Catena, a Germany-based peer reviewed interdisciplinary journal of soil science.

“Such findings help local communities and policymakers in planning sustainable land-use, improving forest and water resource management and implementing slope stability measures,” the Ministry of Science and Technology said on Wednesday.

“This approach can reduce damage to infrastructure, protect livelihoods and enhance disaster preparedness. Moreover, such an approach empowers communities to adapt to climate change and mitigate its impacts on their environment and economy,” the ministry’s statement added.

“Our findings provide a suitable baseline for adapted forest management, sustainability and ground stability measures under ongoing climate warming,” the researchers said. The study enhances the scientific community’s understanding how climate variability, specially the spring and pre-monsoon summer droughts, trigger geo-hazards in the vulnerable Himalayan region.