Relocation of farming land for alleviating land subsidence: a case study of Taiwan

Abstract

Land subsidence attributable to the overuse of groundwater has resulted in severe damage in both urban and rural areas and in developed and developing countries. By incorporating the externality of groundwater use in aquacultural farming, we analyse how the government can mitigate the land subsidence levels without reducing the farmers’ profits, by both reusing the retired aquacultural land and through adjustments in the locations of the species currently being farmed in Tong-shi Township, Taiwan. The simulation results indicate that if the species with high profit can be sustainably raised and moved to aquacultural lands that are less sensitive to groundwater extraction, the total profit could exceed that without the regulation.

Keywords:

• land subsidence
• aquaculture
• retired land

Acknowledgements

We would like to thank anonymous referees for their helpful comments and the National Research Council for its financial support (NSC99-2410-H-006-024).

Notes

1. Although groundwater is also widely used by firms in secondary industries in Taiwan, studies by Chang (2003), the Water Resources Agency (2003), and Chen (2005) all indicate that the land subsidence problems in the coastal areas of Tong-shi have resulted from the activities of aquacultural farmers.

2. For example, areas of fallow lands in Japan amounted to approximately 380,000 ha, or 8% of existing farmlands, in 2005 (Ministry of Agriculture 2006). In Taiwan, 222,709 ha, or 37% of existing farmlands, were left fallow in 2006.

3. Chang (2000) studied land subsidence levels and groundwater use in the Tai-Shi and Mai-Liao areas, which are located along the Chia-Nan Plain watershed, where the soil and hydrologic conditions are similar to those of Tong-shi. The results indicated that 1000 m is a reasonable boundary for the external effect of groundwater use.

4. The survey is based on 42 towns where the aquaculture industry is located.

5. The correlation coefficient between these two variables is 0.51.

6. For example, these reasons can be also found in the research by Huang (2000).

7. From 2000 to 2004, a number of farmers were found to change the species they were raising, and some farmlands were either divided or combined with other such lands. These changes might be attributable to the price fluctuations of agriculture species, land property transfers, etc. For a given piece of farmland, the present assumptions rule out the possibility that the land can be used to raise other species that are different from those raised in 2004. Although this condition may underestimate the profit after the regulation, the most conservative profit estimation for policy use can still be obtained.

8. Based on the information from the Council of Agriculture (2011), the average market prices for tilapia, white-leg shrimp, hard clam and sea bream, which are also the favoured species of farmers in Tong-shi Township, are US$ 1.41/kg, $3.85/kg, $2.83/kg and $4.24/kg from 2007 to 2010. The corresponding standard deviations during this period for these prices are 0.17, 0.21, 0.15 and 0.85, respectively. Although somewhat subjective, the variation is low. If the cost data follow the same trend, the prediction from the proposed model should be reliable.