The Thirsty Terai of Nepal: Groundwater Depletion and Water Insecurity

Introduction

Water is often referred to as the oil of the 21st century, but governments have rarely acknowledged its true value. It is said that we only realize the value of something when we no longer have it. Today, the world is heading down a similar path with our water resources, with pollution, water insecurity, unsustainable consumption, and climate change looming over us.

In 2025, Birgunj, a city in the Terai of Nepal, is facing an unprecedented crisis in water availability for both irrigation and drinking purposes. Tubewells/Handpumps have stopped working, and monsoon rains have been delayed for months. The central and state governments have declared the region drought-prone, but no concrete long-term steps have been taken, nor is there any vision to tackle the problem.

Haphazard pumping of groundwater is seen as the immediate solution to meet demand. However, groundwater is limited, and there are already signs of declining water tables.

This article delves into fundamental questions that must be analyzed and answered for the sustainability of water resources in the Terai of Nepal.

Groundwater: Not Just a Local Problem

Groundwater is not limited to Nepal alone, as it is part of a larger, connected system. The southern Terai plain lies within the Indo-Gangetic Basin, while areas like Dang Valley or Kathmandu Valley have isolated aquifers. The Terai, forming the northern edge of the Ganga Basin, depends heavily on groundwater for domestic and industrial needs.

Figure: *Recharge Potential in Aquifers of Indo-Gangetic Plains (Source)*

Taking too much water from one location affects nearby areas of the aquifer because they are hydraulically connected, and changes in pressure spread through the system. Excessive extraction of groundwater in northern India in the Indo-Gangetic region can therefore influence groundwater levels in Nepal’s Terai as well.

Figure: *Groundwater Quality in the Indo-Gangetic Basin (Salinity and Arsenic Map) (Source)*

There is also an increasing trend of extensive pumping for irrigation. However, global studies confirm that such practices are unsustainable.

Is Groundwater a Sustainable Alternative for Irrigation?

Irrigation requires massive amounts of water and accounts for more than 80% of total demand. Continued extraction of groundwater for this purpose is disastrous, particularly in regions already showing declining water tables. Global studies emphasize that groundwater is a finite source, and heavy extraction is unsustainable.

In the Terai, surface water has been partially utilized for irrigation, but it remains insufficient. Thousands of boreholes are dug each year, and electricity is heavily subsidized for groundwater pumping. While surface irrigation requires large upfront investments and years of planning, it is ultimately more sustainable. The lack of long-term government vision and reliance on short-term measures risk devastating outcomes. Also, changing agricultural practice can help in terms of demand management. Studies show that crop only needs the required moisture rather than flooding fields, where technology can be adopted.

For the irrigation water demand to be fulfilled, interbasin water transfer can also be done.

Interbasin Water Transfer in the Terai of Nepal

Since rainfall, topography, and soil types vary across regions, water availability is not uniform. Some areas have abundant water, while others face scarcity. Transferring water from regions with surplus surface water to water-scarce regions in a sustainable manner is known as interbasin water transfer.

Many rivers in Nepal flow year-round, yet much of their water crosses national borders and drains into the ocean without benefitting anyone. This water could be harnessed in multiple ways, particularly for irrigation and as a source of drinking water, thus reducing the reliance on groundwater.

For Birgunj, two feasible options are the Sunkoshi-Marine and Rapti interbasin water transfer projects. If these projects bring water to the central Terai, they could significantly reduce dependence on groundwater and provide a sustainable water source.

Figure: *Interbasin Water Transfer (Sunkoshi-Marine Diversion Project) (Source)*

One solution might be to focus on surface water for irrigation and groundwater for domestic and industrial use.

Groundwater for Domestic Use: A Sustainable Option?

For a developing country like Nepal, managing large funds for multiple large-scale infrastructure projects is often not feasible. The Terai aquifers, however, are unconsolidated and highly rechargeable through rainfall. Since domestic water demand is much smaller than irrigation demand, extracting groundwater for households may be sustainable for now.

Groundwater in Nepal is generally of good quality in most parts, requiring only basic chlorination. By contrast, surface water demands expensive large-scale treatment plants. Thus, using surface water for irrigation and groundwater for domestic supply could be a sustainable approach provided that extraction amounts are carefully calculated and future demand is considered.

Groundwater monitoring remains fundamental for sustainability, as decisions must be data-driven.

The Importance of Groundwater Monitoring

For groundwater to remain stable, recharge must be equal to or greater than extraction. If extraction and losses exceed recharge, water levels inevitably decline. Seasonal fluctuations occur naturally with levels rising during and after the monsoon and falling in the dry season.

Figure: *Point Observation of Groundwater Table (Piezometric level) post monsoon season in Birgunj (Source)*

To understand long-term trends, monitoring stations are necessary. Aquifers exist at different depths, requiring piezometric monitoring as well as regular testing of water quality. Unfortunately, few such stations exist in the Terai. The government has taken groundwater for granted, failing to recognize its importance. If this continues, future interventions will be costlier and more difficult.

With the failure of handpumps due to lowered groundwater table, the government has prioritized an Isolated boring system for a small house section in the city, which is a bad idea from the management as well as the health and safety perspective.

Isolated Borings: An Unsustainable and Unsafe Practice

With handpumps failing, isolated deep borings have rapidly emerged as a local solution. Typically 4 inches wide and 300–350 feet deep, these borings serve only 60–100 households. In Birgunj alone, an estimated 500–600 such borings are in operation, many using illegal electricity connections. Continuous extraction without regulation is causing significant water loss.

Figure: *Deep Boring for Groundwater Extraction in Birgunj*

These systems also raise public health concerns. Ensuring safe water through chlorination is difficult in small, scattered borings. In contrast, centralized overhead tank systems allow for proper disinfection and skilled operation.

In 2025, a cholera outbreak occurred in Birgunj, which is a water-borne disease. Many people pointed towards the unsafe water supply through isolated deep borings, which cannot be ruled out. The risk of fecal contamination through the unsafe pipe distribution system underscores the dangers. While these systems may appear to address immediate shortages, they are unsustainable and potentially detrimental to public health.

Not only is water security related to water use, but climate change is also impacting water availability in multiple ways.

Climate Change and Water Security in Birgunj

Climate change is compounding the impacts on water scarcity. Rising temperatures increase water demand, leading to more pumping for both drinking and irrigation. Groundwater depletion is further worsened by altered rainfall patterns. Declining precipitation in northern India, linked to Indian Ocean warming, has already reduced groundwater recharge.

Figure: *Yearly rainfall variation (Source)*

Also Read: How Much Does It Rain in Birgunj and Nearby?

Since northern India and the Terai are hydrologically connected, Nepal must learn from both the successes and failures of India’s groundwater management.

Groundwater Trends in India

Unlike Nepal, India has extensive data on groundwater. Over-extraction is widespread due to agricultural demand. A 2009 study showed that 89% of extracted groundwater (221.5 trillion liters) was used for irrigation, while only 11% (27.2 trillion liters) went to domestic and industrial uses. By 2017, the Central Groundwater Board reported significant depletion in states like Punjab, Haryana, and Uttar Pradesh. Nearly 39% of borewells showed declining water levels.

Figure: *Percentage of Extracted Groundwater used in Irrigation in India (Source)*

Uttar Pradesh and Bihar, which border Nepal’s Terai, extract 88% and 80% of groundwater for irrigation, respectively. This raises a pressing question: how much does over-extraction in India affect groundwater in Nepal’s Terai?

In India, more than 70% of food grains are produced using irrigated agriculture, with groundwater pumping as the primary driver of depletion. Groundwater pumping for irrigation remains the primary driver of groundwater depletion.

On the supply side, we should also know how and where the groundwater recharge occurs to better manage the recharge zones.

Groundwater Recharge Zones in Nepal

The Bhabar zone (Area: 4700Km2) is undoubtedly the major groundwater recharge zone for the Terai area, consisting of boulders, pebbles, and cobbles, and having better rainfall than that of the Terai. These areas do not retain water and enter the subsurface, becoming groundwater.

The southern zone (Terai plains) consists of finer material, which has a lower infiltration rate. However, even with less rainfall and lower permeability, the groundwater recharge rates are also high. So, the fact that groundwater only recharges in the Chure-Bhabar area is false.

Figure: *Protest for Protection of Chure-Bharbhar Region (Considered main water recharge zones) (Source)*

As per a study in India, the number of rainy days and rainy days with low-intensity precipitation have significantly declined in India, affecting groundwater recharge during the monsoon season, which remains the key source of supply to groundwater storage. On the other hand, the number of days with high-intensity precipitation has increased in India during the 1951–2018 period.

Groundwater is a resource that can and should be used to benefit people and the environment. However, the sustainable rate of extraction should be known to utilize this valuable resource.

Quantifying Sustainable Pumping

We don’t know exactly what the sustainable extraction amount of groundwater is that we can make from the Terai of Nepal. In India, such studies of sustainability have been done which quantified the sustainable extraction amount from groundwater. However, these studies pointed out that the current abstraction is unsustainable for many parts of India.

As per a study done in India, the total yearly rainfall is 400km3 of water. 17% of the water evaporates back into the air, 53.75% of water becomes groundwater, 28.75% of water becomes river water, and the maximum usable water resource available is 1122 km³ of water.

Similar studies need to be done for Terai as well. Also, as per a study, 50% of the water is not usable due to arsenic and salinity in the Indo-Gangetic basin, which increases the need to quantify the safe, sustainable extraction of groundwater. The findings will guide proper sustainable water management in the Terai of Nepal in a scientific way.

One must know that groundwater also contributes to the water in rivers during the dry season. So, groundwater and surface water are linked.

Rivers as Groundwater in the Dry Season

When rainfall occurs, some water flows into rivers, some evaporates, and some infiltrates to become groundwater. During dry seasons, it is groundwater that sustains river flow. Urbanization and poor recharge management reduce infiltration, lowering river flows and even causing rivers to dry up.

Wetlands are equally important for ecosystems and river flows, and must also be protected.

Figure: *Map Showing Water Interconnected Water Bodies between Nepal and India in Central Terai (Source: Google Earth)*

Conclusion

Groundwater has undeniably improved lives in the Terai by providing an easily accessible source of water. Yet it is a finite resource with clear limits. Unsustainable practices in both supply and demand threaten irreversible damage.

In today’s scientific world, where most problems have solutions, data is key. Integrated Water Resource Management, combined with long-term planning, robust monitoring, and sustainable allocation of groundwater and surface water, is essential. Without such measures, the Terai risks a future where its most valuable reserve, its oil of the 21st century, runs dry.