Articles | Volume 19, issue 7
Research article
31 Jul 2015
Research article |  | 31 Jul 2015

Urbanization dramatically altered the water balances of a paddy field-dominated basin in southern China

L. Hao, G. Sun, Y. Liu, J. Wan, M. Qin, H. Qian, C. Liu, J. Zheng, R. John, P. Fan, and J. Chen

Abstract. Rice paddy fields provide important ecosystem services (e.g., food production, water retention, carbon sequestration) to a large population globally. However, these benefits are diminishing as a result of rapid environmental and socioeconomic transformations, characterized by population growth, urbanization, and climate change in many Asian countries. This case study examined the responses of stream flow and watershed water balances to the decline of rice paddy fields due to urbanization in the Qinhuai River basin in southern China, where massive industrialization has occurred during the past 3 decades. We found that stream flow increased by 58 % and evapotranspiration (ET) decreased by 23 % during 1986–2013 as a result of a three-fold increase in urban areas and a reduction of rice paddy fields by 27 %. Both high flows and low flows increased significantly by about 28 % from 2002 to 2013. The increases in stream flow were consistent with the decreases in ET and leaf area index monitored by independent remote sensing MODIS (Moderate Resolution Imaging Spectroradiometer) data. Attribution analysis, based on two empirical models, indicated that land-use/land-cover change contributed about 82–108 % of the observed increase in stream flow from 353 ± 287 mm yr−1 during 1986–2002 to 556 ± 145 during 2003–2013. We concluded that the reduction in ET was largely attributed to the conversion of cropland to urban use. The effects of land-use change overwhelmed the effects of regional climate warming and climate variability. Converting traditional rice paddy fields to urban use dramatically altered land surface conditions from an artificial wetland-dominated landscape to an urban land-use- dominated one, and thus was considered an extreme type of contemporary hydrologic disturbance. The ongoing large-scale urbanization of the rice paddy-dominated regions, in humid southern China and East Asia, will likely elevate storm-flow volume, aggravate flood risks, and intensify urban heat island effects. Understanding the connection between land-use/land-cover change and changes in hydrological processes is essential for better management of urbanizing watersheds in the rice paddy-dominated landscape.

Short summary
The role of land cover in affecting hydrologic and environmental changes in the humid region in southern China is not well studied. We found that high flows and low flows increased and evapotranspiration decreased due to urbanization in the Qinhuai River basin. Urbanization masked climate warming effects in a rice-paddy-dominated watershed in altering long-term hydrology. Flooding risks and heat island effects are expected to rise due to urbanization.