Background This paper is to study the responses of runoff and sediment characteristics under extreme precipitation conditions in different soil and water conservation measures in the Dali River Basin as an example. To reveal the role of soil and water conservation would provide a reliable theoretical support for floods caused by extreme rainstorm and for prevention of water loss and soil erosion.

Methods Based on the precipitation data, runoff data, and sediment yield data of Suide station of the Dali River Basin from 1964 to 2017, we used Mann-Kendall trend test and linear regression method to analyze the changes in trends. In addition, we used statistical methods to analyze runoff and sediment characteristics in rainstorm floods of July 1964, August 1977 and July 2017 with different periods of soil and water conservation.

Results Under the condition of no obvious change trend of precipitation, the runoff amount and sediment yield of the basin observed from the Suide station in 1964-2017 showed a declining trend. However, different effects were shown on the characteristics of runoff and sediment yield under extreme rainstorm conditions. Under the three extreme rainstorm conditions, the precipitation was basically the same. Compared with July 1964, the runoff in July 2017 and August 1977 was greater than 308% and 120%, respectively, and the sediment yield was greater than 66% and 131%, respectively. However, the runoff in July 2017 compared with the rainstorm in August 1977 was higher than 85% and the sediment yield was lower than 39%. In July 2017, the flood peak flow and flood amount increased significantly, while the sediment yield decreased significantly with the increase of runoff. Flooding in July 1964 and August 1977 were characterized by steep rise and fall of water and a very short duration. In July 2017, the flood showed a steep rise and slow fall of water, and the duration of flood peak significantly prolonged.

Conclusions Soil and water conservation measures in the Dali River Basin have effectively changed the underlying surface conditions and played an obvious role in reducing runoff and sediment yield. However, for soil and water conservation engineering measures, it is difficult to play good benefits of soil and water conservation. These findings indicate that soil and water conservation engineering measures may exert good soil and water conservation benefits within a certain range; while encountering heavy rainfall and flood, soil and water conservation has a limited effect. If a large scale extreme rainfall occurs in the future, the runoff and sediment yield would be also big.