Divergent hydrological responses to intensive production under different rainfall regimes: Evidence from long-term field observations

Abstract

The progress in intensive production over recent decades have greatly altered land-use patterns, often resulting in simplified landscapes. Intensive production is particularly necessary in mountainous areas where arable land resources are scarce, but it is a pervasive concern that landscape simplification will increase pressure for mountain flood disaster control. In this study, rainfall, runoff and sediment process data from 1995 to 2015 were observed for a typical intensively developed mountainous watershed. Data were used to investigate the effects of intensive production on the hydrological response characteristics discharge, suspended sediment concentration, runoff depth, and sediment load under three different rainfall regimes, namely rainfall regimes I (long duration, light rainfall intensity), II (short duration, high rainfall intensity), and III (long duration, high amount). Orchard area in the watershed increased from 4.43 % to 37.44 % under intensive production from 1995 to 2015. Intensive production led to high-intensity land use as well as homogenization and simplification of the landscape, which inevitably caused changes in hydrological processes in the mountainous watershed. Intensive production resulted in a significant downward trend in runoff coefficients (p = 0.001) and sediment loads (p = 0.006) under the three different rainfall regimes. Average sediment concentration decreased significantly and continuously (2394 to 12.53 kg m−3) during the 20 years of the study, and average runoff fluctuated but decreased from 0.218 m3/s in 2000 to 0.093 m3/s in 2015. According to hysteresis analysis, the proportion of counterclockwise loop events decreased after intensive production but remained the dominant circulation mode (40 %). The proportion of events in eight-figure loops increased from 0.06 % before intensification to 25 %. The increase in complex circulation implied that development of intensive production increased the sources of sediment in the watershed. The study increases understanding of hydrological responses to intensive production in complex mountainous watersheds and provides practical references for sustainable watershed management and optimization of land use allocation.