Scientists identify decreasing green cover in Jharkhand

Palamu district in Jharkhand is located in the geographically disadvantageous rain shadow region and is prone to severe droughts. It is home to the renowned Palamau Tiger Reserve and the Betla National Park. In spite of Palamau being declared as an ecologically fragile zone, the loss of forest cover in the recent past is alarming. Palamu used to have 3860 sq km of natural forest area in 2001. The Forest Survey of India (FSI), a government organisation under the Union Ministry of Environment and Forests, has estimated a loss of 333 sq km of forested area during a span of 11 years (from 2001-2011).

Ecologists all over the globe are actively involved in developing novel technologies to help monitor forest change in various parts of the world. Detecting changes on land using satellites is one of the approaches that is widely followed and found to be quite accurate. This information about land changes helps us better understand the relationships and interactions between human and natural environments.

Remote sensing is the scanning of the earth using calibrated cameras installed on a satellite or a high-flying aircraft in order to obtain information about ground features.

Forest area evaluation is usually done manually based on satellite data. Dating back to the early years of remote sensing for air photograph interpretation, manual interpretation involves visually analysing different characteristics of the images at hand. These include studying features like shape, size, and texture of the images. The results tend to vary with different interpreters, as it is subjective. The results are heavily dependent on the experience of the interpreter and the image quality among other details, thus making the manual approach less popular compared to digital classification.

A different method
Now, researchers from the Indian Institute of Science (IISc), Bengaluru, and Birla Institute of Technology, Mesra, have studied the change in forest cover in the Palamu district. They have used spatial data from Moderate Resolution Imaging Spectroradiometer (MODIS) sensor, a payload scientific instrument built by Santa Barbara Remote Sensing. MODIS collects spatial data in the wavelengths ranging from visible to infrared wave frequencies on alternate days, throughout the year.

A common technique of detecting changes is based on comparing 2 satellite images of the same area from 2 different dates. However, advanced techniques now provide the ability to analyse time-series data, i.e. comparing a series of satellite images taken over longer periods of time. “Due to its low cost, ease of availability, and continuity, multi-temporal time series remote sensing data provided us with an enormous possibility for monitoring and characterisation of forest ecosystems,” says Beependra Singh, one of the researchers from IISc involved in this study.

The team compared satellite images of the Palamu region taken every fortnight from 2001 to 2011 with the aid of digital image processing technology. Their study revealed a loss of 293 sq km of forest during the period, coming close to the FSI estimate, but in a quicker way. In addition, the results also revealed the spatio-temporal changing pattern that is so far not revealed in the FSI reports.

As observed by the researchers, there is an accelerated reduction in the forest cover after 2008. This is attributed to the severe droughts that occurred in Palamu in 2005 and 2010. Lack of rainfall gradually resulted in an increased stress on the vegetation, thus drying up the vegetation cover and leading to a degradation of the forested region. In many cases, the degraded forest land made way to extension of agriculture lands, mining and other anthropogenic needs.

This study is an attempt towards satellite based monitoring of changes in the forested region. With all our forests under threat, using remote sensing to observe anomalies and patterns of changes in land cover might help retain what is left.

(The author is with Gubbi Labs, Bengaluru)