Wed, May 04, 2011 - Page 8 News List

Redeploying farming water supplies

By Yu Gwo-Hsing 虞國興

Taiwan’s yearly average rainfall is 2,510mm, approximately 2.8 times the global average, but it is still vulnerable to droughts. That’s because Taiwan has one of the world’s highest population densities and a steep topography that makes it difficult to store water from sudden heavy rainfalls. In terms of climatic conditions, most of the rainfall is concentrated in summer and autumn, when typhoons bring heavy rains. Winter and spring bring very little rain, especially in the south, where the two seasons bring only about one-tenth of the annual rainfall.

Public demand for quality of life do not allow for water stoppages that last several days. Neither can high-tech production at industrial parks withstand a cut in water supplies even for short periods. If the demand for water supply keeps increasing and if global climate change worsens, the nation will not have enough water to get by within a decade.

Faced with this problem, making good use of Taiwan’s more than 820,000 hectares of farmland, and their irrigation and drainage facilities, can help the nation lower the risk of water shortages while also improving its living environment. Taiwan uses about 18 billion tonnes of water per year, with the agricultural sector accounting for the biggest portion at 12.6 billion tonnes — roughly equivalent to that of Japan.

If farmers do not use this water for agriculture and given that most private and industrial users do not have large water storage facilities, this water is left to run off into the sea. Farm hydrology can be deployed to obtain irrigation water and then store that water in fields. Aside from helping the nation meet its agricultural production goals, it can also promote ecological protection and improve the living environment. Sadly, these areas have largely been ignored.

Last year, Russia, one of the world’s major wheat exporters, experienced its severest drought in a century. As Russia banned food exports, global wheat prices fluctuated sharply. This shows how much agricultural production relies on water for irrigation and how vital farm hydrology is. Given the risk that extreme climate conditions could occur anytime, food may not be available on world markets even if one has the money.

In addition to being completely reliant on wheat imports, Taiwan’s food self sufficiency ratio is only about 32 percent, compared with Japan’s 40 percent. This highlights the fragile nature of the nation’s food security and highlights the importance of agricultural irrigation and hydrology.

Water for agricultural land irrigation nourishes the soil, which is beneficial to the ecology, biodiversity and improving the local environment. By contrast, industrial wastewater must be purified and the cost of recycling water is about NT$300 to NT$500 per tonne, which adds to environmental and social costs. Because agriculture is more tolerant to water shortages, experts in farm hydrology management can use existing water collection and supply facilities and irrigational management technology or stop land cultivation and irrigation during droughts to offer timely support to the water needs of private and industrial users, thus effectively meeting the goal of social safety and sustainability.

Not only are global climate changes intensifying the scale of droughts, we are also seeing record-breaking rainfall each year. For example, Typhoon Fanapi in six hours brought as much rain as Kaohsiung was projected to receive once every 200 years, clogging drainage canals and causing massive flooding. The construction of flood detention ponds has recently drawn wide attention, but aside from being difficult to build, obtaining land is also a problem. Paddy fields are actually like artificial flood detention ponds. Taiwan’s irrigated paddy fields can absorb about 330 million cubic meters of water, roughly equivalent to the Feicuei Reservoir’s (翡翠水庫) water storage capacity. They can thus effectively reduce the impact of flooding and minimize the loss of lives and possessions.

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