Abstract
Changes in soil moisture following the establishment of sponge cities play a key role in the regulation of the relationship between surface runoff and rain resources in arid and semi-arid regions of the Loess Plateau. Based on soil moisture and rainfall monitoring data obtained at the fine-scale (per 10-cm depth and hourly), temporal and spatial variation in soil moisture under different sponge measures and their responses to rain events were analyzed, in addition to water quality changes were investigated by water sampling. The results showed, from 2000 to 2018, the area of farmland greatly decreased from 56.88 % to 5.02 % in Guyuan, while the area of construction land increased from 29.24 % to 45.96 %. The area of changes in Guyuan accounted for 63.68% of the total area. Precipitation in July and August was large, and accounted for 19.11% and 23.24% of the multi-year average precipitation, respectively. The grasslands and sunken green spaces exhibited good water retention effects, with average soil moisture of 14.40 % and 13.77 % during the study period, and 18.48 % and 15.52 % during the rain event, respectively. During the rain event, the total nitrogen (TN), ammonia nitrogen (NH3-N), available phosphorus (AP) and total phosphorus (TP) can be effectively reduced by the sunken green spaces, with average concentrations of 0.79 mg/L, 0.28 mg/L, 0.03 mg/L and 0.05 mg/L, respectively. The development of sponge measures could improve the urban ecological environment and hydrological conditions in the Loess Plateau, and increase the potential utilization of urban rainwater resources.
Highlights
With the implementation of the reform and opening up policy in China, remarkable social and economic developments have been observed, and urbanization rate increased from 17.55% in 1977 to 57.35% in 2016 (Chen, 2007; Liu and Luk, 2009; Wang et al, 2017a)
Soil moisture was higher in the three sponge measures in summer and autumn compared to spring and winter (Figure 10), and this may be affected by rainfall, which was similar to the results of previous studies (Liu and Shao, 2014; Wang et al, 2015; Liao et al, 2017; Xu et al, 2017)
Soil moisture in the sunken green spaces and grassland increased with an increase in soil depth, which was more pronounced in fall, which may be mainly because time changes in soil moisture were affected by climatic factors
Summary
With the implementation of the reform and opening up policy in China, remarkable social and economic developments have been observed, and urbanization rate increased from 17.55% in 1977 to 57.35% in 2016 (Chen, 2007; Liu and Luk, 2009; Wang et al, 2017a). Heavy rains and floods hit Effects of Sponge City Development about 200 cities annually in China (Yin et al, 2015; Sang and Yang, 2017; Lyu et al, 2018c). The construction of a sponge city was proposed in 2012, and the concept of low impact development was adhered to in the development of sponge cities in China (Xia et al, 2017; Yuan et al, 2017; Wang et al, 2017b). Regulating urban hydrological processes and increasing the storage capacity of urban rainwater are key goals in the development of sponge cities, and since 2015, a pilot sponge city is being constructed in China (Sang and Yang, 2017; Xia et al, 2017)
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