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：农业土地利用因农业气候条件产生的季节性变化，会对流域水循环造成影响。本研究旨在探究位于巴西巴拉那州（PR）弗朗西斯科·贝尔特朗市城区上游、其径流最终汇入马拉卡斯河上游河谷的流域内，农业土地利用季节性动态所固有的径流时间变化特征。本研究借助HEC-HMS模型，在7个降雨重现期下设置12个月度土地利用情景并模拟径流峰值，以此验证径流的影响效应。结果显示，裸地与径流峰值间存在显著相关性：从时间维度来看，4月与3月为径流产出量最高的时段，1月与8月则为最低时段。经量化，每平方公里裸地对应的径流峰值增幅介于0.78至1.64立方米每秒之间。此外，对历史降雨数据的梳理还显示，10月同样易产生大规模径流。综上，径流峰值增幅与裸地占比间的强相关性可被高精度量化，但要明晰径流与洪涝风险的时间分布特征，还需结合历史降雨记录进行综合研判。