降雨强度对西南喀斯特坡地土壤水分及产流特征的影响

降雨强度是水文过程的重要影响因素，为揭示其对喀斯特坡地土壤水分及产流特征的影响，本研究以桂西北典型喀斯特坡地为研究对象，采用野外人工模拟降雨方法，在相同降雨量（200 mm）下，对不同降雨强度下（34.8 mm/h、73.2 mm/h、100.0 mm/h 和136.4 mm/h）坡地土壤水分动态变化及产流过程进行研究。结果表明：1）随着土层深度的增加，土壤水分对降雨的响应趋于迟缓；由于喀斯特坡地土壤导水率较大，在不同坡位和土层深度，土壤水分变化迅速，通常在24 h 内恢复到降雨之前的水平，表明土壤层蓄水能力低，水文过程迅速。2）随着降雨强度的增大，累积地表径流量、壤中流量及表层岩溶带径流量均呈增加的趋势，表明随雨强的增加，喀斯特坡地水分由垂向（深层渗漏为主的慢速流）转为侧向运移（不同径流成分的快速流）。3）地表径流、壤中流及表层岩溶带径流与土壤含水率存在明显的产流阈值关系，且径流产生与消退过程和土壤含水量存在滞后效应，表现为顺时针（壤中流）或逆时针（表层岩溶带径流）的“绳套关系”。本研究表明喀斯特坡地产流主要受控于土壤- 表层岩溶带界面稳定入渗率，表现为受降雨强度的影响较大，研究结果有助于深入了解喀斯特关键带水文循环。

Study on soil moisture variation and runoff characteristics on typical karst slope under different rainfall intensities

Rainfall intensity is an important factor in hydrological process, in order to reveal its influence on soil moisture dynamics and runoff characteristics on karst slopes, four field rainfall simulation experiments were conducted with rainfall intensities ranging from 34.8 to 136.4 mm/h, on a typical karst slope of northwest Guangxi, in southwest China. The results showed that: 1) with the increase of soil depth, the response of soil moisture to rainfall was lagging by soil layers. At different depths and slope positions, the soil moisture changed rapidly, which rapid increase during the onset of rainfall and rapid decline quickly after the rain had stopped, and returned to the original levels prior to rainfall within 24 h, indicate a low soil water storage capacity and rapid hydrological processes on karst slopes. 2) The cumulative of surface, subsurface, and epikarst runoff showed increasing trend with the increasing of rain intensity, which means that water movement transform from vertical to lateral with the increasing of rain intensity. 3) There was a significant threshold relationship between soil moisture and runoff generation, and observed hysteresis phenomenon in the relationships between soil moisture and runoff. This study revealed that rainfall intensity significantly affects near-surface hydrological processes on karst slopes, our data contribute to a more comprehensive understanding of water cycle in karst critical zone.