Tropical montane areas of Southeast Asia are exposed to high-intensity rainfall during the monsoon period. This is particularly problematic in areas where soils on steep slopes are cultivated as it can lead to heavy runoff, high soil erosion, and water pollution. The objective of this paper is to analyse the effect of the impact of raindrops on the dynamics of runoff on such steep fields. Experiments under simulated rainfall were performed at the plot scale (1 m2) to quantify water export from the surface of upland agricultural soils during overland flow events. Four 1 m2 plots were divided in duplicated treatment groups: (a) control with no amendments, and (b) amended with pig manure. Each plot was divided into two 0.5 m2 rectangular subplots. One subplot was designated as a rain splash treatment; the other sub-plot was covered with a 2 mm grid size wire screen that was located 12 cm above the soil surface. The purpose of the screen was to break the raindrops into fine droplets and to reduce fall height in order to drastically reduce their kinetic energy. Runoff was measured for each sub-plot. The results show that raindrop impact drastically enhances runoff generation on both bare soils and on manure amended soils. When the impact of raindrops was limited by screening, runoff was higher on amended soils than on bare soils. The temporal evolution of runoff was correctly modelled using a soil hydraulic conductivity that exponentially decreases over time of exposure to rainfall. Both experimental and modelling results showed that droplet energy induces a rapid evolution of the hydraulic properties of the soil surface due to crusting, resulting in a reduction of hydraulic conductivity and a concomitant increase in runoff rate.

中文翻译：

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雨滴影响对水力传导率和地表流强度的短期影响的实验和建模证据

东南亚的热带山地地区在季风期间会受到强降雨的影响。这在种植陡坡土壤的地区尤其成问题，因为这会导致大量径流、严重的土壤侵蚀和水污染。本文的目的是分析雨滴对这种陡峭田地径流动力学的影响。在地块规模 (1 m2) 下进行模拟降雨实验，以量化地表水流事件期间高地农业土壤表面的水输出。四个 1 平方米的地块被分成重复的处理组：（a）没有修改的对照，和（b）用猪粪修改。每个地块被分成两个 0.5 平方米的矩形子地块。一个子地块被指定为雨水溅处理；另一个子地块用 2 毫米网格大小的金属丝网覆盖，位于土壤表面上方 12 厘米处。屏风的目的是将雨滴打碎成细小的水滴，并降低下落高度，从而大大降低它们的动能。为每个子小区测量径流。结果表明，雨滴的影响极大地增强了裸露土壤和粪便改良土壤上的径流生成。当雨滴的影响被屏蔽限制时，改良土壤的径流高于裸土。使用土壤水力传导率正确模拟径流的时间演变，该土壤水力传导率随着暴露于降雨的时间呈指数下降。实验和建模结果都表明，由于结壳，液滴能量引起了土壤表面水力特性的快速演变，