场次降雨条件下考虑田梗高度的农田产流规律模拟

Simulation of farmland runoff generation pattern considering the field ridge height under rainfall event conditions

条块分割、田埂密集是海河平原农田的典型特征,科学认知田埂作用下的农田产流规律对解析平原区水循环演变过程至关重要。目前,流域尺度的农田产流规律的研究较少,关于降雨特征-田埂高度-农田产流三者之间的影响关系还不明晰,田埂作用下的农田产流规律是平原区水循环演变解析的薄弱环节。该研究基于CMOPRH遥感降水数据产品分析了海河平原场次降雨特征,并以Smith&Parlange入渗模型为核心构建农田积水产流模型,模拟海河平原降雨-产流过程。结果表明:1)海河平原场次降雨总量以小于25 mm为主,占降雨总场次的95%,10 h以内的场次降雨占比为96%,降雨总量和降雨强度由东北部向西北部递减;2)在2008—2019年降雨条件下,模拟无田埂、10 cm田埂、12 cm田埂、15 cm田埂四种情景的农田年均产流量,结果分别为62.4亿m^(3)/a、19.7亿m^(3)/a、13.1亿m^(3)/a、5亿m^(3)/a;3)田埂高度已知的条件下,降雨历时和降雨强度是影响农田产流的关键因素,以降雨历时为横坐标、降雨强度为纵坐标,可以通过拟合反比例函数曲线划分一场降雨是否产流;4)根据海河平原历史农田面积变化估算,2000年海河平原农田产流量相对1979年减少10.2亿m^(3),2016年农田产流量相对2000年减少5.1亿m^(3)。该研究定量解析了降雨特征、田埂高度对农田产流的影响,为解析海河平原区地表水资源衰减原因提供了重要的规律认知。

Runoff generation can be greatly varied in the events, such as the climate, catchment properties, and scale under the action of field ridges in farmland. It is crucial to better understand the spatiotemporal patterns of runoff generation for the process-based hydrological modelling. The evolution of the hydrologic cycle in the plain areas can also be strengthened to link the run-off behavior associated with the changes in environmental and land use conditions. However, it is still lacking on the relationship between the rainfall characteristics, ridge height, and the runoff generation in farmland. Taking the Haihe River Basin in northern China as the research area, this study aims to characterize the rainfall events using the Climate Prediction Center(CPC) Morphing Technique(MORPH, CMOPRH) remote sensing precipitation data products. Smith-Parlange infiltration method was used to construct a water flow model for the farmland accumulation, and then to simulate the rainfall and runoff generation process in the study areas. The results are as follows. 1) The total amount and duration of rainfall events in the study Plain were mainly less than 25 mm and 10 h in the field, accounting for 95% and 96% of the total rainfall events,respectively. In rainfall intensity, the light, moderate, and heavy rain accounted for 87%, 11%, and 1.9% of the total rainfall,while the rainstorm only accounted for 0.1% of the total rainfall. There was also a significant decrease in the total amount of rainfall and rainfall intensity from the northeast to the northwest. 2) The mean annual runoff was 5.47 billion m^(3) in the study area from 2008 to 2019, of which the farmland runoff was 2.18 billion m^(3), accounting for about 40% of the total runoff.Specifically, the yield of the Tuhaimajia River Basin was the highest, with an annual mean of 1.95 billion m^(3), whereas, that of the Ziya River Basin was the lowest, with an annual mean of 100 million m^(3). Four scenarios of no ridge, 10, 12, and 15 cm ridge were simulated under the rainfall conditions from 2008 to 2019, where the annual mean runoff generations of farmland were 6.24, 1.97, 1.31, and 0.5 billion m^(3)/year, respectively. 3) Once the height of ridge was the constant, the rainfall duration and intensity were the key factors to affect the runoff generation of farmland. An inverse proportional function curve was fitted to classify the rainfall whether the runoff generation or not, where the rainfall duration and intensity were taken as the horizontal and vertical coordinate, respectively. For example, the runoff was formed at the ridge height of 10 cm, where the rainfall intensity was 10 mm/h, and the rainfall duration was more than 15.9 h. Once the rainfall intensity was 30 mm/h, and the rainfall duration was 2.4 h, the farmland runoff was formed in the study area. 4) The amount of farmland runoff decreased by 1.02 billion m^(3) in the study area in 2000, compared with 1979. This variation was attributed to both the evolution of the farmland area and the transition from no ridges to ridges in simulation. The amount of farmland runoff decreased by 510 million m^(3) in 2016, compared with 2000, which was mainly influenced by the decrease in the farmland area.Correspondingly, there was a significant decrease in the farmland runoff, due mainly to the decrease in the farmland area during the acceleration of urbanization in the study areas since 2000. Anyway, the quantitative analysis was offered to clarify the effects of rainfall characteristics and ridge height on farmland runoff generation. The finding can provide a strong reference to explore the causes of surface water resource attenuation in the Haihe plain area of northern.