Abstract
It is imperative to know the spatial distribution of vegetation trends in India and its responses to both climatic and non-climatic drivers because many ecoregions are vulnerable to global climate change. Here we employed the NDVI3g satellite data over the span of 35 years (1981/82–2015) to estimate vegetation trends and corresponding climatic variables trends (i.e., precipitation, temperature, solar radiation and soil moisture) by using the Mann–Kendall test (τ) and the Theil–Sen median trend. Analysis was performed separately for the two focal periods—(i) the earlier period (1981/82–2000) and (ii) later period (2000–2015)—because many ecoregions experienced more warming after 2000 than the 1980s and 1990s. Our results revealed that a prominent large-scale greening trend (47% of area) of vegetation continued from the earlier period to the later period (80% of area) across the northwestern Plain and Central India. Despite climatologically drier regions, the stronger greening trend was also evident over croplands which was attributed to moisture-induced greening combined with cooling trends of temperature. However, greening trends of vegetation and croplands diminished (i.e., from 84% to 40% of area in kharif season), especially over the southern peninsula, including the west-central area. Such changes were mostly attributed to warming trends and declined soil moisture trends, a phenomenon known as temperature-induced moisture stress. This effect has an adverse impact on vegetation growth in the Himalayas, Northeast India, the Western Ghats and the southern peninsula, which was further exaggerated by human-induced land-use change. Therefore, it can be concluded that vegetation trend analysis from NDVI3g data provides vital information on two mechanisms (i.e., temperature-induced moisture stress and moisture-induced greening) operating in India. In particular, the temperature-induced moisture stress is alarming, and may be exacerbated in the future under accelerated warming as it may have potential implications on forest and agriculture ecosystems, including societal impacts (e.g., food security, employment, wealth). These findings are very valuable to policymakers and climate change awareness-raising campaigns at the national level.
Highlights
The main component of the terrestrial biosphere is vegetation and it plays an active role in the climate system through the exchange of energy, carbon, water and momentum between the biosphere and the atmosphere [1,2]
Compared to the earlier period, greening trends were more pronounced in the later period, especially over the Northwest India (Gujarat and Rajasthan) and Central India (Madhya Pradesh) (Figure 2b)
With the help of 35 years of satellite normalized difference vegetation index (NDVI) records, we investigated the greening and browning trends of vegetation separately over two focal periods (i.e., 1981/82–2000 and 2000–2015) in relation to both climatic and non-climatic factors
Summary
The main component of the terrestrial biosphere is vegetation and it plays an active role in the climate system through the exchange of energy, carbon, water and momentum between the biosphere and the atmosphere [1,2]. Over the Indian continental regions, average temperatures during the summer monsoon season (June–September) have increased by 0.25 ◦ C since the mid-1990s [5] and are projected to rise by up to 2.8–3.8 ◦ C in the future in response to the build-up greenhouse gases in the atmosphere [6,7]. Previous findings suggested that the increasing rainfall trends are more profound west of 80◦ E, whereas largely negative or decreasing trends are present towards the eastern region [10]. This asymmetry in trends of monsoon rainfall between eastern and western segments is mostly associated with changes in large scale thermodynamic parameters, such as wind speed and moisture content [11]
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