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The Thar Desert in India saw a striking 38 per cent rise in greening annually over the last two decades, driven by a significant increase in monsoon rainfall and agricultural expansion, a new study showed. It has shed light on how the landscape of the Great Indian Desert has changed, impacted by both climate change and anthropogenic pressures.
Groundwater resources have also contributed significantly to vegetation growth, the report Greening of the Thar Desert driven by climate change and human interventions highlighted. At the annual scale, groundwater accounted for 55 per cent contribution and precipitation for 45 per cent, it indicated.
In fact, Thar was the only desert in the world with the highest concurrent increase in population, precipitation and vegetation during the last few decades, scientists from IIT Gandhinagar and Bay Area Environmental Research Institute, NASA Research Park in the US established.
Thar region, which hosts the world’s highest population density for a desert, spans 200,000 square kilometres across northwestern India (Rajasthan, Gujarat, Punjab and Haryana) and southeastern Pakistan. The scientists analysed all the 14 major deserts across the globe during 2000–2020 and found that the region experienced the highest population growth.
Defying the trend of expansion of arid areas, the desert experienced a 64 per cent rise in precipitation between 2001 and 2023 — increasing at a rate of 4.4 millimetres / year after 2000, the report showed. The annual rainfall increased across the Thar region, particularly in the northwest and primarily during the summer monsoon.
The analysis was based on data from Climate Hazards Group InfraRed Precipitation with Station (CHIRPS), which combines in-situ and satellite-based precipitation observations.
Among the 14 major deserts, only four (Thar, Arabian, Negev and Eastern Gobi) showed a significant increase in precipitation and one (Namib) experienced a substantial decline in precipitation during 2001–2023, the study found. The remaining nine major deserts did not experience a significant change in mean annual precipitation.
The researchers termed the increased precipitation as “opposing effects of climate change”. These changes contributed significantly in vegetation growth in the deserts — all four major deserts with a significant increase in precipitation also experienced a significant increase in vegetation during 2001–2023, according to the study.
Thar’s extensive greening was driven by large-scale monsoon changes coupled with groundwater pumping for irrigation purposes, government interventions in building irrigation infrastructure and power supply.
“For instance, climate change can limit water availability, while human interventions associated with irrigation and groundwater pumping can sustain crops in water-limiting environments,” the authors wrote.
During the summer monsoon season, precipitation accounted for 66 per cent of the greening, while groundwater contributed 34 per cent. However, in the non-monsoon season, groundwater was the major driver of vegetation growth (67 per cent). Annually, the contributions were more balanced, with groundwater accounting for 55 per cent and precipitation for 45 per cent.
The team of researchers — Vimal Mishra, Hiren Solanki and Ramakrishna Nemani — examined the spatial changes in annual vegetation greening calculated from the moderate resolution imaging spectroradiometer (MODIS) and precipitation from the CHIRPS dataset during 2001–2023.
Comparing the seasonal cycle of mean monthly greening for the 2001–2010 and 2011–2020 periods, the team found that the region experienced a substantial increase in vegetation greenness during the summer monsoon (June–September) and non-monsoon (October–May) seasons.
The region experienced a significant agricultural expansion, with crop area increasing by a major 74 per cent and irrigated area by 24 per cent during 1980–2015. Similarly, there was a significant expansion in the gross (95 per cent) and net (58 per cent) irrigated areas during the same period.
The summer monsoon season overlaps with the Kharif season, the major crop-growing period for the region. “While Kharif season crops meet a large fraction of the total water requirement from the summer monsoon rainfall, crop growth during the Rabi season largely depends on irrigation from surface water and groundwater resources,” the authors wrote.
The scientists used in-situ observations of well levels from the Central Ground Water Board (CGWB) and satellite observations from Gravity Recovery and Climate Experiment (GRACE) for the 2002–2021 period to examine the potential impacts of groundwater pumping on its storage variability in the Thar region.
As agriculture activities expanded, the intensive use of groundwater has caused groundwater depletion in the Thar, reflecting an imbalance between water extraction and recharge rates.
Most groundwater wells showed a decline in water levels, especially in the north-central region, where vegetation greening had increased significantly during the monsoon and winter seasons.
Several regions within Thar showed a 50 per cent to even 800 per cent rise in urban areas during 1985–2020, the report showed.
The Thar region's population growth during 2000–2020, was followed by the Arabian Desert, while most other deserts did not experience a considerable increase in population, the study showed.
“This population growth in the Thar region is evident from the expansion of urban areas and cropland, likely driven by cultivation potential and relatively lower land prices. Water availability also played a crucial role in urban settlement and agricultural expansion. For instance, the Indira Gandhi Canal surface water sourced from north India and enhanced water availability in the northwest parts of the Thar Deser,” it said.
The scientists estimated projected changes in precipitation to assess what the future holds for the Thar Desert’s observed greening.
Depending on the emission scenario and period (near, mid and far), an increase of 20–50 per cent in the mean annual rainfall was projected in the region.
“While the agricultural and urban expansion in the Thar region has been remarkable, sustaining it in the future might be challenging. Despite the rise in the summer monsoon rainfall, a substantial increase in dry and moist heat extremes during the summer and monsoon seasons may pose challenges for energy demands for cooling and irrigation, reduce labour capacity and lead to water scarcity during the dry season,” the study warned.