- Indian scientists have developed a soil loss map of Uttarakhand that will help pinpoint areas battling soil erosion and the degree of severity of top soil loss brought on by a combination of both human-induced and natural factors.
- Close to 50 percent of the state’s area is above the tolerance limit of soil loss. Sheet erosion and landslides contribute substantially to soil loss resulting in the decline of productivity of agricultural land.
- Anthropogenic activities like uncontrolled deforestation and unscientific land-use, including shifting cultivation, have accelerated the process of soil erosion. The major causes of erosion in the state could be attributed to weak geological formation, active seismicity and deforestation.
A team of scientists has generated a soil loss map of Uttarakhand, a state in the northwest Himalayas that often makes headlines for devastating landslides and floods that sweep away houses and bury people in their wake, amid unbridled developmental activities.
The map, based on a soil erosion study of the state, pinpoints areas battling soil erosion and the degree of severity of top soil loss brought on by a combination of both human-induced and natural factors, scientists said. It would aid foresters, agricultural experts and conservationists to assess soil quality in these stretches and take appropriate measures to arrest dwindling quality of soil in the state.
The study highlights that sheet erosion and landslides contribute substantially to soil loss resulting in the decline of productivity of agricultural land.
“When we speak of landslides and floods, it is also important to note that soil quality has been degrading in the state. The state is located in one of the most hazard-prone belts in Asia and is susceptible to earthquakes, landslides and floods. Deforestation is one of the major factors behind soil erosion,” soil scientist and study author S.K.Mahapatra told Mongabay-India.
The analysis underscored the importance of diversification of agricultural practices to include farm-forestry, agro-horticulture and/or agro-forestry to stymie soil loss in cultivated areas of the state.
“Close to 50 percent of the state’s area is above the tolerance limit of 11.2 tonne per hectare per year of soil loss,” Mahapatra, Principal Scientist, ICAR-National Bureau of Soil Survey and Land Use Planning, told Mongabay-India.
The major causes of erosion in the state could be attributed to weak geological formation, active seismicity and deforestation. Anthropogenic activities such as uncontrolled deforestation and unscientific land-use, including shifting cultivation have accelerated the process of soil erosion.
Heavy rainfall, weak geology
Plagued with heavy rainfall and a weak geology, Uttarakhand in 2013, witnessed one of India’s worst natural disasters since the December 2004 tsunami, when a multi-day cloudburst centred on the state, caused devastating floods and landslides.
According to the Geological Survey of India, over 5700 people were reported dead and over 4,200 villages were battered by the floods and post-floods landslide in 2013.
Incidences of houses being swept away and people buried underneath rubble, during monsoons, continue rocking the state even today. As recent as August 28, 2018, heavy rains triggering landslides killed three people in Tehri district.
When it comes to soil erosion, the state not only has to grapple with the geological vulnerabilities but anthropogenic pressures such as population and demands for fuel and timber add complexity to the mix.
The geological formation of the entire northern region of India, including Uttarakhand is weak and unstable. Geotectonic movements make the land mass unstable, resulting in landslides and mass movements, the study points out.
“Further, soils of this region are developed on stratified soft sedimentary and tertiary rocks, which are also susceptible to erosion. These soils easily detach during the incessant rains or cloud bursts and move along the slope with the flowing water causing sheet erosion,” Mahapatra explained.
Incidents of widespread deforestation and mining in many parts of the state are common, the study notes. “Very good dense forests are being converted into poor stock, thin degraded fallow lands. Considerable areas under forest have been brought under agriculture in the recent past. Deforestation and forest degradation are the leading causes of water erosion in undulating and steep-sloping hills,” he said. Water erosion is the detachment and removal of soil material by water.
According to 2017 government data, the state has a recorded forest cover area of 24,295 square kilometre, which is almost half (45.43 percent) of the state’s geographical spread. However, this is only a marginal increase of 23 sq km forest cover since 2015.
Despite a slight uptick in very dense forest cover, moderately dense forests have shrunk and a net decrease of 49 square km of forest cover (within recorded forest area) has been observed due to rotational fellings and developmental activities.
In between, in 2016, Prime Minister Narendra Modi laid the foundation for the highly-publicised Char Dham all-weather project connecting the “Char Dham”, the four holy sites for Hindus – Yamunotri, Gangotri, Kedarnath and Badrinath.
The ambitious project involves improvement and development of 900 km length of national highways coursing their way through the ecologically and geologically fragile terrain. It is reported that 23,000 trees have already been axed on a 285 km stretch of the project.
Dissecting severity of soil loss
Surface soil is lost every year from different regions of the state leading to a huge amount of nutrient loss in a year. “In terms of fertiliser loss, this accounts for a staggering loss of nutrients in a year,” pointed out Mahapatra. Under these circumstances, adoption of suitable soil and water conservation measures is necessary to conserve biodiversity and sustainability, Mahapatra said.
“Conservation measures can have only a short-term impact, unless they are accompanied by objectives to tackle the underlying causes. The knowledge of the causes of soil erosion and adoption of appropriate conservation measures is essential for sustainable productivity in the state,” the authors note in the study.
Based on the degree of severity of soil loss, as pointed out in the map, necessary water and soil conservation steps need to be taken up to mitigate top soil loss in the fragile ecosystem.
Tapping into the integrated use of geographic information system (GIS) and universal soil loss equation (USLE), the most widely accepted and utilised soil loss equation for over 30 years, Mahapatra and colleagues showed that close to 50 percent of the state’s area is above the tolerance limit of 11.2 ton per hectare per year of soil loss.
This is a limit that denotes the maximum level of soil erosion that will permit crop productivity to be sustained economically and indefinitely.
The analysis shows that 6.71 percent area of the state (about 359,000 hectares) faces “moderately severe” (15 to 20 tonne/hectare/year) soil erosion, while close to 9 percent (473,000 hectares) of the state is battling “severe” (20 to 40 tonne/hectare/year) soil loss.
But what has got alarm bells ringing is the extent of “very severe” soil loss. Data reveals close to one-third of the area of the state (32.72 percent or1,750,000 hectares) is experiencing soil loss at a rate of 40–80 tonne/hectare annually.
Districts of Dehradun, Uttarkashi, Tehri Garhwal, Rudraprayag and Chamoli, which are also tourist hotspots, fall in the “severe” category while Bageshwar comes in the “very severe” line-up.
“The data clearly indicates that about 48.3 percent area of the state is above the tolerance limit of 11.2 tonne/hectare per year of soil loss,” the study said.
While assessing soil loss, besides rainfall, factors such as slope length, soil erodibility and management factors, cover factor was also considered.
Potential of soil erosion usually increases if the soil has no or very little vegetative cover. “Vegetative cover of plants and/or crop residues are considered as the kind that protects soil from raindrop impact and splash and thus reduces soil loss,” he said.
Agronomy needs remedying
Only 14 percent of the state is sown with crops while net irrigated area is 0.06 percent. Owing to the stony nature of land, crop cultivation is mainly undertaken in the river valleys and terraced slopes. Most of the agriculture in the state is rainfed.
Mahapatra recommends marshalling agronomic measures along gentle sloping areas to maximise conservation of rainwater to reduce run-off and soil nutrient loss.
For example, farm operations such as ploughing, seeding and intercropping along the contour lines or across the slope, in conjunction with contour farming help in the formation of natural ridges and furrows, which act as a series of mini barriers and reservoirs to intercept rainwater.
Contour farming refers to the practice of ploughing and/or planting across a slope following its elevation contour lines. “Contour farming is generally practised by farmers for the sake of convenience, which speeds up run-off resulting in more run-off and soil erosion,” Mahapatra said.
In 2016, industry body ASSOCHAM said the state has recorded poor crop productivity. “Considering that topography of Uttarakhand is characterised by sandy soils that do not retain water and due to unavailability of moisture in the soil, state has recorded poor crop productivity, so much so that agriculture sector clocked just about three percent CAGR (compound annual growth rate) between 2004-05 and 2014-15,” the body said in its report.
Besides, intercropping allows growth of canopy legumes such as groundnut, green gram, black gram, soybean and cowpea in inter-row spaces of crops like maize, sorghum and castor.
“This provides adequate cover on the ground and thereby reduces erosion risk apart from biological insurance to increase productivity of rainfed arable lands. Tillage makes the soil surface more permeable to entry of rainwater. This practice also reduces run-off, soil and nutrient loss and enhances crop yields,” Mahapatra said.
Mulching is an important agronomic practice which not only prevents soil erosion by dissipating kinetic energy of raindrops but also facilitates infiltration, reduces evaporation and improves soil structure which eventually enhance crop yield.
In low-rainfall areas, mulching helps in conserving moisture in the soil profile while in high rainfall areas, it reduces run-off and soil loss, resulting in higher crop yields.
As for mechanical measures, contour bunding, benched terracing and grassed waterways have been suggested.
Mahapatra, S. K., Reddy, G. P., Nagdev, R., Yadav, R. P., Singh, S. K., & Sharda, V. N. (2018). Assessment of soil erosion in the fragile Himalayan ecosystem of Uttarakhand, India using USLE and GIS for sustainable productivity. CURRENT SCIENCE, 115(1), 108-121. http://www.currentscience.ac.in/Volumes/115/01/0108.pdf.
Banner image: A 2014 picture of the landscape eroded by flash floods and landslides, surrounding the path leading to Kedarnath temple. Photo by Kartik Chandramouli.