How irrigated farms generate rainfall for nearby rainfed crops across India

Rainfed farming forms the backbone of Indian agriculture, supporting over 60% of the total cultivated area and playing an essential role in national food security. The vast majority of these crops rely heavily on the annual monsoon between July and September, which provides up to 70% of the country's rainfall. Even during the post-monsoon months of October through December, crops depend on the residual soil moisture left behind by those summer rains. Because the margin for error is so slim, even a minor rainfall deficit of 10% to 15% can drop national food grain production by up to 10 million tonnes.

While most of India’s rain originates from ocean evaporation over the Arabian Sea and the Bay of Bengal, land-based water sources also play a vital role in sustaining rainfall. Water evaporating from forests, natural vegetation, and soil creates atmospheric moisture that falls back to the earth as local rain—a process known as moisture recycling that accounts for up to 18% of global crop production. However, scientists have historically paid very little attention to how artificial farm irrigation acts as a similar, complementary source of recycled rainfall.

This phenomenon is especially relevant in India, where irrigated farmland and rainfed crops exist in close geographic proximity. As water evaporates from heavily irrigated fields, prevailing winds carry that atmospheric moisture downwind toward neighboring rainfed farms, where it can precipitate as rain. This process is particularly active in the Indo-Gangetic Plains, one of the most intensively irrigated regions in the world, where vast irrigated tracts sit directly adjacent to extensive rainfed farming areas.

The moisture generated by upwind irrigation is especially valuable during the non-monsoon season, when ocean winds carry far less moisture and overall rainfall is scarce. While this evaporation from irrigated fields offers a crucial secondary lifeline for rainfed crops growing outside the main rainy season, researchers have yet to fully measure or quantify just how much rainfed agriculture truly relies on this upwind moisture.

A recent study titled 'Irrigated agriculture supports rainfed crops in India through atmospheric moisture recycling' by Akash Koppa and others published in Environmental Research Letters attempts to evaluate the reliance of rainfed crops on irrigated agriculture in India. 

How much does evaporation from irrigated farms contribute to rainfall

Average Rain Contributions Across India

• National Average: Across India's rainfed farming regions, water evaporating from upwind irrigated fields supplies an average of 7% of the total rainfall.

• Regional Differences: This contribution varies widely depending on location.

• The Indo-Gangetic Plains (IGP): Because this area has far more irrigated fields than the rest of the country, upwind irrigation provides over 20% of the local rainfall over rainfed fields. During dry years, this contribution becomes even higher, helping offset rainfall deficits.

• Northwestern India: In semi-arid northwestern states, high levels of irrigation contribute significant moisture to the air, which is amplified by the dry local climate.

• Southern India: Dry areas in southern India have similar climate conditions but far fewer irrigated farms, resulting in much smaller moisture contributions. This shows that the density of irrigated farms is the main factor driving this effect.

The Role of Irrigation Water in Rainfall

• Share of Recycled Moisture: Water added through artificial irrigation makes up between one-third and one-half of all recycled land moisture that falls back to the ground as rain.

• Share of Total Rainfall: Irrigation evaporation contributes a maximum of 6% to total overall rainfall.

• Strongest Areas: This effect is most noticeable in the heavily irrigated Indo-Gangetic Plains. It is also significant in dry western states like Rajasthan and Gujarat, where irrigation is the primary water source and plays a major role in feeding clouds.

Seasonal Patterns

• Monsoon Season (June–September):

  • Irrigation contributes the least to rainfall during these months because natural rain is already the main water source.

  • However, moisture still rises from irrigated fields, providing up to 20% of the rainfall over rainfed crops in certain regions.

  • This creates a moisture loop: water applied to fields in one area evaporates, moves downwind, and generates rain for another area.

• Rabi Season (October–March):

  • Rainfed crops rely mainly on soil moisture left over from the monsoon, along with winter rains.

  • Natural evaporation from unirrigated land contributes more to rainfall than irrigation water during this period, even though total rainfall is low.

• Zaid Season (March–June):

  • This is the driest time of the year with the lowest overall rainfall.

  • Irrigation water becomes essential; in March, evaporation from irrigated fields supplies up to 8% of the total rainfall over downwind rainfed crops, despite low overall cropping levels (around 20%).

Moisture Recycling and Crop Water Stress

• National Impact: Without recycled moisture from upwind fields, crop water stress across India rises by an average of 1.5%.

• Indo-Gangetic Plains (IGP) Impact: In the IGP, losing this recycled moisture increases crop stress by an average of 8%, rising as high as 15% in dry years.

• Peak Stress Levels: If irrigation evaporation were completely removed, rainfed crops in the IGP would face stress levels above 15%—about three times their annual average—for over a month during critical growing periods.

What could happen in the case of absence of moisture recycling from irrigated fields 

Crops experience the greatest water stress during the middle and late stages of growth — the very phases most critical for productivity.

• Mid-season stress reduces photosynthesis, which lowers biomass.

• Late-season stress shrinks grain size, leading to major yield losses.

The study shows that in the complete absence of moisture recycling from upwind irrigated fields, stress levels rise to their upper limit. In practice, other land covers like bare soil, grass, or trees would still release some moisture, but without irrigated crops the buffer is much weaker.

Planning and managing irrigated and rainfed agriculture holistically can help strengthen regional food and water security

The study shows that irrigation doesn’t just benefit local fields — it also feeds moisture back into the atmosphere, which can return as rainfall over nearby rainfed and irrigated crops. This recycling effect is strongest in the Indo-Gangetic Plains (IGP), but also significant in western and southwestern India, where irrigation is less widespread today.

Irrigation recycling efficiency ranges between 5% and 15%, peaking in the pre-monsoon months (up to 12.5%), when extra rainfall is most valuable for crop growth. In the IGP region, recycled irrigation conserves up to 0.05 km³ of water annually, reducing pumping needs. Across India, this represents about 1.8% of irrigation water saved, rising to 8% in parts of the IGP. This volume represents a potential direct saving in both water resources and the energy required for pumping.

The study argues that irrigation recycling efficiency should thus be considered as one of several criteria—alongside conservation of natural vegetation, sustainable blue water use, and socio-economic factors, among others, when assessing the feasibility and desirability of irrigation expansion in regions in India. Beyond supporting remote rainfed crops, atmospheric moisture recycling also creates a potential benefit for irrigated crops themselves. Evaporated irrigation water can precipitate back over the same or downwind irrigated regions, inducing a positive feedback loop that reduces the net demand for irrigation from surface or groundwater sources. 

The study argues that most large-scale investments and subsidies in India have traditionally favoured irrigated agriculture, often at the expense of rainfed farming. Examples include power subsidies for irrigation and financial incentives to convert rainfed areas into irrigated ones. While discussions highlight the need to plan irrigated and rainfed systems together, this study adds a new dimension: it shows that the two are not just linked socially and economically but also physically connected through atmospheric moisture recycling because:.

• In India, irrigated and rainfed crops often grow side by side, making this atmospheric link especially strong.

• The connection is most critical in the non-monsoon months, when rainfall is scarce. Moisture recycling helps reduce water stress during the mid- and late stages of crop growth, which are decisive for yields.

Thus, recognising this physical link is important and can help rebalance incentives, ensuring that support for irrigation also strengthens resilience for rainfed farming. Irrigation expansion is not just about supplying water locally. It creates a feedback loop that sustains rainfall, reduces crop stress, and even saves water and energy. Recognising this atmospheric link can help design smarter policies that integrate irrigated and rainfed systems, especially during the dry months when crops are most vulnerable.