SEASONAL DYNAMICS OF AGRICULTURAL SOIL COVER IN RUNOFF GENERATION

ABSTRACT Seasonal changes in agricultural soil use due to agroclimatic conditions affect the water cycle in watersheds. This study aimed to understand the temporal variation of runoff inherent to the seasonal occupation dynamics of the agricultural soil in the basin that drains the upper valley of the Marrecas River, upstream of the urban perimeter of Francisco Beltrão, PR. The effects of runoff were verified through flow peaks simulated by the HEC-HMS model in twelve monthly soil use scenarios, under seven precipitation return periods. The results indicated a strong relationship between bare soil and flow peaks, temporally delimiting April and March as the largest runoff generators and January and August as the smallest ones. The ratio quantified by rates of increase in flow peaks ranging from 0.78 to 1.64 m3 s−1 per km2 of bare soil. In addition, the survey of historical precipitation data also warns of the generation of large runoff volumes in October. Therefore, the strong correlation between the increase in flow peaks and occupation by bare soil can be quantified with good precision, but it is also necessary to consider historical precipitation records to understand the temporal distribution of runoff and flood risks.

摘要：受农业气候条件制约的农业用地季节性变化，会对流域水循环产生显著影响。本研究以巴西巴拉那州（PR）弗朗西斯科贝尔特朗市城区上游、汇出马雷卡斯河（Marrecas River）上游河谷的流域为研究对象，旨在阐明该流域农业用地季节性动态占用所固有的径流时间变化规律。研究通过HEC-HMS模型，对12个月度土地利用情景下的7个降雨重现期的洪峰流量进行模拟，以此验证径流效应。结果表明，裸土占比与洪峰流量之间存在极强的相关关系，时间维度上可界定为：3月与4月为径流产生量最大的时段，1月与8月为径流产生量最小的时段。经量化，洪峰流量增幅介于0.78~1.64 m³·s⁻¹·km⁻²（以每平方千米裸土计）。此外，历史降雨数据调研还警示，10月同样会产生较大径流量。综上，洪峰流量增长与裸土占用占比之间的强相关性可被高精度量化，但同时也需结合历史降雨记录，方能全面理解径流的时间分布特征与洪水风险。