- 2025 marks four decades of India’s national programme on wetlands. A national wetlands inventory has been an important focus area of this programme.
- There have been efforts to collate national statistics on the extent of wetlands in the country and these have evolved progressively with improvements in cartographic technologies and capacities, especially with the increasing sophistication of the remote sensing programme.
- Wetlands inventory should take an interdisciplinary approach and involve not just capturing wetlands extent but also wetlands condition and should be repeated over time to provide comparable and scientifically defensible information on the overall status and trends in wetlands.
- The views in this commentary are that of the author.
In March 2024, India’s Space Application Center (SAC) published a high-resolution remote sensing assessment and analysis of Indian wetlands. This publication, the 2024 Atlas, is a geo-spatial database of Indian wetlands at 1: 12,500 scale, classifying them under 20 wetland types. The extent of the wetlands is assessed using pre and post-monsoon images of 2018 and 2019 from the high-resolution LISS-IV sensor on the Resourcesat-2/2A satellite. An unspecified number of wetlands have also been ground-truthed or validated by site visits, to enhance the image interpretation and analysis accuracy.
The total wetland area in India is estimated to be 16.89 Million hectares, which is about 5.12 percent of the country’s total geographic area. Of the 3.58 million wetlands mapped, 2.49 million have an area equal to or greater than 0.1 ha and 1.09 million wetlands have an area less than 0.1 ha.
The 2024 Atlas has been prepared under Phase 2 of the National Wetlands Inventory and Assessment programme of the Department of Space, Government of India and led by the Space Applications Centre (SAC) of the Indian Space Research Organization in collaboration with 30 partners, most being state remote sensing application centres.
Using a higher resolution satellite sensor, the 2024 Atlas was able to map even smaller wetlands, with a minimum area of 0.1 hectares, compared to the 2022 Atlas which could map only those wetlands with an area greater than 2.25 ha.

Progressive developments in wetland atlases
The 2024 Atlas is the fifth in the series which applies earth observation to assess the extent of the wetlands in the country. There has been a progressive sophistication in imageries used, which has enabled better mapping of even the smaller wetlands in the country.
The previous atlases, with the first iteration being in 1998, used a coarse mapping resolution wherein wetlands were mapped at a scale of 1:250,000 for most parts of the country, barring the northeast wherein mapping was done at 1: 50,000 scale. The 2011 Atlas, which was based on LISS III data of 2007-08, was the first to include an estimate of wetlands under the minimum mapping threshold of 2.25 ha, indicating that the country potentially had 0.55 million wetlands less than 2.25 ha area. However, in 2023, the first census of water bodies published by the Ministry of Jal Shakti, using data from 2018-19, enumerated 2.42 million waterbodies spread over an area less than 0.5 ha. The 2024 Atlas seems to have bridged this anomaly by reporting that the country has 3.23 million wetlands with an area of less than 2 ha.
Unfortunately, as most of these Atlases use a different scale and data resolution, most of the wetland extent estimates are not comparable, except for the 2022 Atlas. The 2022 Atlas presents a comparison between the extent of the wetland reported in 2006-7 and 2017-18 and has indicated that the number and extent of wetlands with area equal to or greater than 2.25 ha has increased in the intervening period. The 2022 Atlas also noted that in this period, natural coastal wetlands declined while the area of mangroves, creeks and coral reefs increased. A significant reduction in the inter-tidal mudflats and salt marshes was noted. The natural inland wetlands increased marginally during this period. This specific change in natural inland wetlands calls for close introspection. Wetlands are usually formed in topographic depressions and shaped over a long period by complex geological and hydrological processes. However, the formation of new natural inland wetlands in a short timeframe of a decade, as the report shows, is likely because of human-induced landscape alteration or increased fragmentation. It is thus hard to track how much wetlands the country has lost over time. A global study published in Nature in 2023 with a longer-term reconstruction of natural wetland change suggests that India may have had 61.3 million hectares of natural wetlands in 1700, nearly halved to 37.2 million hectares by 2020. India has been indicated as one of the top three countries (after the United States and China) in terms of wetlands loss during 1700 – 2020.
However, none of the wetlands extent change studies capture the dynamics in the country’s various ecosystems, particularly the small wetlands. Small wetlands, such as johads in Haryana and Rajasthan and the tanks in Southern India, play a multitude of roles in a landscape, such as provisioning water, regulating water quality, providing habitats for various species, especially amphibians and insects, mitigating flooding, and acting as vital corridors for wildlife movement. Even though they may appear insignificant in size compared to larger wetlands; these ecosystems play a significant role in overall ecosystem health and functioning, particularly in local environments.
Read more: [Commentary] Latest wetland mapping data underscores the need to step up conservation action
A closer look at the recent wetlands atlases
The 2024 Atlas and 2022 Atlas are based on remote sensing images of only a year’s difference. However, surprisingly and counter-intuitively, the 2024 atlas reports that wetland area has reduced in several categories. But it also reports a significant increase in the overall number of wetlands in different categories.
The 2024 Atlas and its three iterations present wetlands area and numbers by classifying wetlands into 20 different types. This classification has been modified from the Ramsar typology. The third level classification used in the atlas is a hodge-podge (at times, vegetation is used, and for others, inundation and elevation for high-altitude wetlands). A separate waterlogged category is used, wherein most wetlands could eventually be placed. Similarly, the class High altitude wetlands may include other wetland classes, such as lakes.
It is highly likely that the differences in wetland areas and numbers between 2024 Atlas and 2022 Atlas are due to inconsistent classification.
Several wetland types, such as peatlands, seagrass meadows, and karst wetlands, do not find coverage in these atlases. The seamless vegetation map of India for 1992-2012, published by ISRO in collaboration with several institutions, provides details on forested swamps and marshes which are otherwise missing in the national atlas.
The extent of wetlands represented by the atlas may, therefore, at best, serve as the lower limit of wetland extent in the country.
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Producing wetlands atlas using remote sensing is an arduous task
Mapping wetlands using remote sensing techniques is a complex and arduous task. The term wetlands groups together a range of aquatic ecosystems which are not unified by a common land cover feature (for example, vegetation in forests). While the presence of water is a distinguishing feature, water may be present seasonally or permanently and at the surface or below the surface with a range of variations during the year and between the years, not all of which can be discerned through remote sensing images. Steep environmental gradients in and around the edges of the wetlands, such as boundaries between wetland vegetation and terrestrial vegetation, are challenging to resolve only using remote sensors. Finally, the highly dynamic nature of wetlands significantly alters their reflectance and energy backscatter properties.
The wetland atlases produced to date use optical remote sensing, which primarily uses sensors mounted on satellites to measure how light reflects off the earth surface.
A range of indices are used to combine wavelength ranges (also called bands) to extract wetland signatures such as inundation, hydric soils and presence of hydrophytic vegetation. Most of the thresholds used in these indices need an element of human judgement, and thus, ground-truthing of representative points is required in order to resolve interpretation errors. But for a large country like India, producing high-accuracy maps becomes a tedious task and needs to be supported, at the very least, by remote sensing and GIS teams working in tandem with wetland ecologists. Discrepancies between wetlands extent derived from satellite data and ground conditions are common due to factors like seasonal variations, mixed-pixel effects and classification thresholds. Addressing these challenges requires integrating robust ground validation framework, multi-temporal analysis to account for dynamic changes, and teamwork across disciplines to improve accuracy and reliability.
Optical images alone may not be sufficient to map the total wetland extent in its full diversity. For mangroves and forested wetlands (such as Myristica swamps), augmenting optical data with shortwave infrared channels has provided good discrimination from adjoining natural forests and plantations. Peatlands, which are incredible carbon pools, have failed to figure in any wetland assessment thus far, despite their presence being recorded in the high-altitude Himalayas and coastal regions. Radar satellite observations, which allow penetration below the canopy, have been globally found useful for mapping these wetlands. Similarly, unique coastal wetlands such as seagrasses can be mapped using hyperspectral aerial photographs, which can not only assist in distinguishing these wetlands but also compute features such as species composition, percentage cover density and leaf area index. Segregating perennial from non-perennial wetlands effectively may best be done with a mix of optical and synthetic aperture radar data.
Read more: [Explainer] What are wetlands and why do we need to protect them?
The need for a systematic wetlands inventory programme for India
It is high time that sporadically produced wetlands atlases at differing resolutions render into a systematic national wetlands inventory programme for the country. The broad purpose of this programme, in line with Ramsar Convention recommendations, would be to support the goal of the national wetlands programme (the National Plan for Conservation of Aquatic Ecosystems), which is “developing and maintaining a network of healthy wetlands which contribute to human well-being through their diverse ecosystem services, as well as sustaining diversity and populations of wetland-dependent species”. An implicit goal is to support implementation of wetlands regulatory framework, especially the Wetlands (Conservation and Management) Rules, 2017, by specifying clear wetland boundary and change over a baseline. This also acquires significance as the Supreme Court in India, in its order of December 11, 2024, has directed all States and Union Territories to ground-truth and demarcate all wetlands indicated in 2021 Atlas within three months.
For wetlands inventory to support effective programming and policy-making, the least information that needs to be captured is the status and trends in wetlands extent and their condition. The information on wetlands extent needs to be produced at a consistent scale and updated regularly, say every two years, to generate information on trends. It is also pertinent that the wetland extent maps are validated on the ground.
Besides extent data, information on wetlands condition needs to be discerned. The United States, for example, conducts a wetlands condition assessment, which is published every five years. The assessment is designed to answer questions about the extent to which nation’s wetlands support healthy ecological conditions and the prevalence of key stressors at the national and regional scale. The assessment complements the United States Fish and Wildlife Service Wetland Status and Trends Program, which characterises changes in wetland acreage across the conterminous United States. The two assessments provide policymakers with comparable, scientifically defensible information documenting the current status and trends in both wetland area and ecological condition.

Foundational to the national wetlands inventory is an accepted wetlands classification system, which is representative of the diversity of wetlands and addresses the various policy and programmatic needs. Classification systems based on ecosystem structure attributes (such as hydrology or plant communities) do not readily lend themselves to attribution of ecosystem functions (such as their ability to moderate floods and droughts), which are more relevant for the use of inventory information by different sectors. Countries like the United States, Brazil and South Africa have therefore included classification systems that can also address ecosystem functions by bringing in attributes such as the direction of water flow and relative position in a basin. This is also important as the goal of mainstreaming wetlands in sectoral planning requires a description of ways in which wetlands can address sectoral challenges such as flood and drought mitigation and pollution abatement.
There is also a need to develop a wetlands delineation protocol so that wetlands map produced by different agencies and organisations follow a common standard and are comparable.
The inventory has to be tailored to the needs of various stakeholders, particularly wetlands managers and state wetlands authorities, who are entrusted with the ground implementation of various programmes. Wetlands atlases currently provide information on wetlands extent and in some cycles, minimum and maximum inundation variability, transparency and chlorophyll. These are insufficient to produce a target setting or identify priority areas. The possibility of overlaying wetlands data with other datasets, such as land use and land cover, drainage basins, population density, linear infrastructure and others, would improve the usability of these maps for management applications.
The mapping of wetlands can be significantly improved by combining optical and radar imageries. Application of advanced technologies such as LiDAR (Light Detection and Ranging) and InSAR (Interferometric Synthetic Aperture Radar) can help improve mapping accuracy. The InSAR can detect water level changes, whereas LiDAR provides elevation data that can provide better insights into the physical features and hydrological regimes that govern wetlands. However, a robust ground-truthing of the maps and data is necessary.
Wetlands inventory should take an interdisciplinary approach – and involve, at the very least, ecologists and wetlands practitioners along with GIS and remote sensing specialists. It is essential to factor in the needs and perspectives of the state wetland authorities and field managers regarding the kind of data that is needed to support wetland conservation actions. Developing the capacities of wetlands managers in wetlands inventory and delineation would also improve the application of such data in management planning and monitoring.
The author is the Director of Wetlands International South Asia. He is also a Ramsar Convention’s Scientific and Technical Review Panel member.
Banner image: Kakodonga river in Assam. Image by Anupon sarmah via Wikimedia Commons (CC BY-SA 3.0).