Does Rice Have to Be a Swamp?

 

Rice is the most eaten food on earth — and, because of the methane emitted by flooded paddies, one of the most climate-intensive. Together with Hi-Rice we measured two farms in Thailand down to the litre of diesel per hectare. The numbers surprised us a little.

Rice is a special case on the global climate radar. It feeds more people than any other food, and it is the one large staple crop whose standard farming method — a field held under water for months — emits methane into the atmosphere in a systematic way. Between 11 and 12 percent of the world’s methane emissions from agriculture come from rice paddies¹. For a food that appears three times a day on plates across much of Asia, that is not a footnote. It is a climate question.

Together with the company Hi-Rice we looked at one specific version of this global picture: two Thai pilot farms growing jasmine rice — one in Chonburi on the Gulf coast, one in Buriram in the drier northeast. Two climates, two soils, two ways of running a farm. We recorded diesel use, fertiliser quantities, irrigation regimes, straw handling and harvest volumes, ran a full life cycle assessment on them, and compared the result to the best available Thai reference data². The dataset that came out surprised us a little.

 

 

What happens on the farm

 

The families behind the numbers. Every figure in this study — from the tractor’s fuel to the water level in each paddy — comes from questionnaires they filled out with us, field by field.

The first numbers we are about to show refer to the rice just after harvest — to everything that happens up to that point: tillage, seed, fertiliser, crop protection, water, straw handling, harvest machinery. That is the so-called “cradle to farm gate” level. For rice, most of the footprint arises in the field anyway, long before the grain is loaded onto anything. If the numbers are good there, half the battle is already won. After that, we follow the grain further — through the mill, the sea route to Europe, and packaging in Switzerland — until it reaches the shelf.

 

 

The results, unvarnished

 

Overview — jasmine rice at harvest. Comparison of the two Hi-Rice pilot farms against Thai reference values we calculated by combining literature data with statistics on cultivation methods and yields.2 Three findings stand out.

Climate footprint. The Hi-Rice fields produce between 1.52 kg (Chonburi) and 1.65 kg (Buriram) of CO₂ equivalents per kilogram of harvested rice. The Thai average is 2.39 kg. That is 31 to 36 percent below the national mean — and still below the “best case” for conventional Thai rice cultivation (1.68 kg), the value we derived by combining the most favourable common cultivation methods. The single biggest lever here is the irrigation strategy. Where the field is drained in phases instead of held under water continuously, the soil gets oxygen and the methane-producing microbes lose their footing — once water returns, it takes several days before methane production picks up again. We therefore did not set methane to zero, but applied the IPCC emission factors for AWD (alternate wetting and drying) — the practice used on these farms. Methane is still produced under AWD, just much less than under permanently flooded fields. A large part of the climate gap to the Thai average can be explained by this avoided share — methane that would have been released under continuous flooding, but is not under AWD3.

Water footprint. The gap is even wider here. 0.24 to 0.32 m³ of water per kilogram of rice on the Hi-Rice fields, versus 1.56 m³ on average in Thailand. That is 80 to 84 percent less. The biggest lever, again, is the irrigation strategy: where cultivation runs on natural rainfall and targeted top-up irrigation, rather than on continuously flooded fields, water demand per kilogram of yield drops sharply. Thailand’s calculated “best case” sits at 1.09 m³ per kilogram — four times more than on the Hi-Rice fields.

Water scarcity. This is the regionally weighted figure — it captures how scarce the water actually is where it is taken from. In Chonburi the value is 0.008 m³-eq/kg, only 2 percent of the Thai average. In Buriram it is 0.23 m³-eq/kg, or 68 percent. The wide range — between 32 and 98 percent below the mean — is not a measurement error. It reflects the fact that Chonburi, on the coast, sits in a region with substantially more available water than the semi-arid northeast where Buriram is located. The finding also says: even where water is regionally tight, Hi-Rice cultivation puts noticeably less pressure on the local system.

 

From field to shelf

So much for the grain at the edge of the field. What happens after that? In the mill, 1.24 kg of harvested paddy turns into 1 kg of polished, white jasmine rice — the husk is removed; some of it becomes broken grain and bran. The rice is then loaded into 25 kg sacks or one-tonne big packs and sets out on its way: roughly 17,000 kilometres, the lion’s share by sea to Switzerland. No aeroplane, no refrigerated container. Only after arrival is it packed into its retail format — a paper box (just under 24 grams) — and grouped into shipping cartons that hold several boxes each, adding another 16 grams of cardboard per kilogram of rice.

 

The climate verdict is clear-cut: three stars in both regions. On water, we get back the split picture that was already visible in the raw data — Chonburi sits in a region with plenty of water, Buriram does not. Since around 87 percent of Hi-Rice’s volume comes from Buriram, that asymmetry shows up in the volumeweighted overall rating: three stars for the climate footprint, one star for water. That is the honest answer. The cultivation in Buriram is climate-friendly, but it takes place in a region where every litre used carries a heavier regional weight.

 

What’s going well — and what remains open

Three things stand out about these farms that show up in the numbers. The fields are not held under water permanently, only in phases. Fertiliser is applied in two or three doses instead of one pre-planting load — that reduces leaching. And on the farms we measured, the pumps run on electricity from solar panels rather than on diesel.

What the numbers don’t answer belongs here too. Two pilot farms are two pilot farms — they are not a region. The irrigation strategy that produces these values is demanding and cannot simply be transplanted to every topography. And the regional water scarcity in Buriram is not something a single farm can solve on its own; it depends on the climate and the groundwater table of an entire province. Still: when a staple that is treated worldwide as climate-intensive produces roughly a third fewer emissions than usual at its origin — and does not lose that lead on the way to the Swiss shelf — it is a hint that how the crop is grown matters more here than whether you eat rice or another starch.

 

Why we got involved in this project at all

Eaternity has been building food life cycle assessments for more than fifteen years. Most of the products we assess are already on the supermarket shelf, and we rank them by climate impact. Hi-Rice is one of the rare cases where we calculate deep into the upstream supply chain, before the product even exists — field by field, based on questionnaires filled in by the farmers themselves. That is laborious and unspectacular.

 

But 80 to 90 percent of rice’s footprint arises in the field — to improve the balance of a single grain, that is where you have to start.

 

References

1. Nikolaisen, M. et al. (2023). Methane emissions from rice paddies globally. Nature Food 4, 1–9. doi.org/10.1038/ s43016-023-00711-2.
2. Mungkung, R. et al. (2019). Water footprint inventory database of Thai rice. Kasetsart University, Bangkok. Used as reference dataset for Thailand (average, best case, worst case). Supplemented by: Arunrat, N. & Pumijumnong, N. (2017). Practices for Reducing Greenhouse Gas Emissions from Rice Production in Northeast Thailand. Agriculture 7(1), 4. doi.org/10.3390/agriculture7010004.
3. Sriphirom, P. et al. (2019). Effect of alternate wetting and drying water management on rice cultivation. Journal of Cleaner Production 223, 980–988. doi.org/10.1016/j.jclepro.2019.03.212.

 

Download PDF