Zonal differences of runoff and sediment reduction effects for typical management small watersheds in China

In this particular study, 99 typical managed small watersheds which representing five water erosion areas in China were selected to study zonality of Runoff Reduction Efficiency (RRE) and of Sediment Reduction Efficiency (SRE). The RRE is the ratio of Effect of Runoff Reduction (ERR) by soil and water conservation measure over management degree in a watershed. And The SRE is the ratio of Effect of Sediment Reduction (ESR) by soil and water conservation measure over management degree in a watershed. First of ah, statistical analysis was applied to test the zonal effects of RRE and SRE between different water erosion regions. The results showed that the mean RRE values in northern regions were significantly greater than those of southern regions; and the mean SRE values in northern regions were significantly greater than those in southern regions. Next, the variation of RRE with runoff depth (H) was studied in direction of both latitude and longitude across regions influenced by East Asian Monsoon. Meanwhile, the variation of SRE with specific sediment yield (Y) was studied in direction of both latitude and longitude across regions influenced by East Asian Monsoon. The results showed that RRE had the inverse variation trend as H in both latitude and longitude direction and SRE had the same variation trend as Y in both latitude and longitude direction. Furthermore, the variation of unit management area Runoff Reduction Rate (RRR) with H and RRE was studied in direction of both latitude and longitude. And the variation of unit management area Sediment Reduction Rate (SRR) with Y and SRE was studied in direction of both latitude and longitude. It was found that RRR had the similar variation trend as H in latitude direction and there was critical point around 37°N greater than which RRR began to be equal to H or even larger; RRR had the similar variation trend as H in longitude direction and there was a critical point around 109°E lees than which RRR began to equal to or greater than H; SRR had the similar variation trend as Y in latitude direction and there was critical point around 36°N greater than which SRR began to be equal to Y or even larger; SRR had the similar variation trend as Y in longitude direction and there was a critical point around 106°E lees than which SRR began to equal to or greater than Y. The zonality of RRE, RRR, SRE and SRR was determined by the combined influence of climate variation and special landform in regions controlled by East Asian Monsoon in China.