Improved simulation of surface runoff and soil erosion in no-till rural catchments to adapt agricultural production systems to the impacts of climate change.

The repercussions of climate change have great potential to cause negative impacts on water resources and agriculture. The IPCC reported that high magnitude and intensity rainfall will increase in southern Brazil, increasing its potential to degrade natural resources. In addition, more severe droughts will lead to frequent crop failures and reduced water availability. Despite the wide adoption of no-till farming in Brazil, its efficiency in managing runoff has not been enough to control soil degradation and its impacts on water resources. The lack of runoff control practices amplifies the negative effects resulting from climate change. This new climate scenario, associated with the simplification of the production system, must be understood by employing a strategy that combines hydrological monitoring and mathematical modeling of small rural catchments. The soil and water degradation in no-tillage systems are still poorly understood and not properly incorporated into hydrologic and erosion models. The objective is to improve the runoff and erosion simulation strategy based on hydrological monitoring at the landscape scale. Therefore, this study evaluated the hydrology and erosion processes of agricultural slopes under no-tillage system under different runoff control conditions by monitoring 63 rainfall events in two 2.4-ha zero-order catchments and 27 rainfall events in four 0.6-ha macroplots. Monitoring was performed in southern Brazil (29°13'39"S, 53°40'38"W) in the Southern Plateau characterized by a wavy relief and deep and highly weathered soils. The catchments are paired and similar in terms of the type of soil and relief, but different regarding the presence of broad-based terraces. The macroplots have different soil and crop management systems. By using monitoring techniques, the hyetographs, hydrographs and sedigraphs revealed the influence of the different land managements on the infiltration, runoff generation and propagation, and sediment yield. The broad-based terraces reduced runoff by 56% and sediment yield by 58.7%. The results in the macroplots showed that high amounts of phytomass and/or chiselling do not control runoff in medium and high magnitude events. Crop management including an increased phytomass input efficiently controlled sediment yield (63%), although it did not reduce runoff volume and peak flow. In contrast, scarification had no impact on runoff and sediment yield. Monitoring results indicate the need for additional measures to control runoff (terraces), even in areas under NT and with high phytomass production. The monitoring data set is also being used to improve the mathematical models to describe the hydrological and erosive processes under no-till farming. From the improvement of simulations, soil and water conservation techniques is recommended to adapt the agricultural production system to intense rainfall with positive repercussions to soils and water resources. The study emphasizes the importance of monitoring at the catchment scale to better understand the hydrological behaviour of agricultural areas and provide the necessary parameters to effectively control runoff.