Rice fields as natural infrastructure for groundwater recharge
- Kumamoto, Japan

Groundwater abstraction

Kumamoto Prefecture is famous for its high-quality and abundant groundwater reserves. With over one million inhabitants, including close to 700,000 residing in Kumamoto City, this population and other sectors (agriculture and industries) are mainly dependent on groundwater for water supply. High precipitation (average 2,200 mm/year) and permeability of the deposits have created groundwater storage in confined and unconfined aquifers. In 2015, domestic water supply accounted for 72% of the water use, while agriculture and industries accounted for 9% and 8%, respectively. Groundwater came under pressure from an increasing demand for water in the city, industries and agriculture. There was also decreasing recharge conditions due to urbanisation and industrialisation, as well as changing farming practices. These conditions posed a looming water security risk for Kumamoto.

In response, the city initiated efforts to conserve groundwater resources through measures such as the installation of groundwater observation wells. The industrial and agricultural sectors also made efforts to reduce groundwater withdrawals, while abstraction from the city saw a slight increase. Studies found that enhancing recharge is a viable nature-based solution to combat increasing groundwater demand and decreasing recharge conditions caused by land-use changes. Abandoned rice fields along the Shirakawa River were found to be ideal for groundwater recharge, as water can be taken from local streams and the river during the wet season, and can be used as source water for recharge through existing irrigation canals. However, creating a scientific basis and an enabling institutional environment to undertake groundwater recharge was quite challenging.

Payment for ecosystem services to incentivise groundwater recharge

Payment for ecosystem services (PES) could be a cost-effective solution to implement groundwater-based natural infrastructure. The major challenge for establishing a PES scheme, however, is uncertainty related to the invisibility of the hydrogeological processes, the fate of recharged water, as well as how to administer the scheme in a transparent manner. After consultation with stakeholders, a voluntary offsetting scheme was devised, in which major groundwater users (Kumamoto City water utility and the private sector) agreed to pay farmers for allowing them to flood unused rice fields for groundwater recharge. After the flooding season and during the rest of the year, the farmers can still grow other crops (such as vegetables). In addition, as a voluntary scheme, farmers are free to start cultivation and terminate the agreement anytime. The scientific base helped establish a standard payment rate which was based on equivalent flooded area per month (hectares [ha] per month) as a unit. Participating farmers were paid JPY 11,000, JPY 16,500 and JPY 22,000 for flooding a 1,000 sq.m rice field for 1, 2 and 3 months, respectively. It was a win-win option, because the farmers could get direct cash payments, while the city and private sectors could offset their groundwater abstraction in a transparent manner. The PES for groundwater recharge was a good deal for a mostly ageing farming community facing the impacts of declining rice consumption and a falling market price for rice.

Success factors and sustainability of PES

The PES scheme has been fully functional since 2004. Strong interest and support over the past 14 years is a testimony to the success of the scheme. Developing a scientific understanding of the recharge using rice fields, as natural infrastructure, was fundamental to its success. Groundwater experts and researchers, mainly from local universities, played a pivotal role in establishing the technical feasibility and viability of PES. Groundwater modelling and verification of the fate of infiltrated water by regular monitoring of groundwater levels reinforced the scientific basis behind the PES scheme. Flexibility on the flooding condition was also important for convincing farmers. They are free to use their fields for cropping during non-flooding periods. The scheme has attracted other private sectors, and the recharge area per month (hectares per month) has more than doubled from 291 ha/month in 2004 to an estimated 636 ha/month in 2018. The PES scheme has received a positive response from many stakeholders in Kumamoto, such as the city government, university, Kumamoto Groundwater Foundation, farmers, industries and local non-profit organisations (NPOs). The scheme even received the 2013 ‘Water for Life’ UN-Water Best Practices Award. Groundwater recharge is now one of the highest water resource management priorities of the city water conservation division. The Kumamoto City Water Source Forest Development Policy 2004 identified the role of forests in contributing to groundwater recharge and flows of major rivers, and the prefecture maintains a forest area of about 900 ha. After the success of the PES scheme, another indirect approach to offsetting groundwater abstraction also evolved there. Under this approach, agricultural products grown/raised (rice, vegetables, cows) in the fields along the Shirakawa River are labelled and sold as eco-products. For instance, purchasing 1kg of eco-rice is equivalent to recharging 20 cubic meter. Similarly, each 100g meat of “rice cow” (i.e., cows raised by feeding on rice grown in the recharge fields) will contribute to 20 cubic meter of recharge while growing the feed. The sale of eco-labelled products (e.g. under the brand name Mizu-no-Megumi, meaning “water’s blessings”) is a way to encourage more farmers to grow rice by providing additional co-benefits, such as better market publicity and premium prices. The eco-product idea has expanded into other areas, where it promotes reduced pesticide use and organic fertilizers to reduce the negative impact on groundwater quantity. As of 2017, 38 offices and organisations located mostly in Kumamoto and other parts of Kyushu, such as JA Kikuchi, are associated with this offsetting initiative and support the promotion of eco-labelled agricultural products.

A common question that arises is the feasibility of transferring the PES scheme to finance similar kinds of nature-based solutions (NbS) to other countries. Japan has a conducive environment for implementing market-based instruments, so it was relatively easy to implement the PES scheme, considering the importance of groundwater for the city’s water security as well as the mature agricultural business. It could be argued that a similar PES idea may be less feasible in developing countries, especially due to the rate of payments. However, the important lesson is the viability of a NbS if it is backed by sound research and implemented effectively. Climate funds could be strategically diverted to establish a similar PES scheme to support NbS.