Current Location:home > Browse

1. chinaXiv:202005.00093 [pdf]

Flow regime changes in three catchments with different landforms following ecological restoration in the Chinese Loess Plateau

LUO Zhidong; LIU Erjia; QI Shi; ZHAO Nan; SUN Yun
Subjects: Biology >> Botany >> Applied botany

The Chinese Loess Plateau is known as one of the most severe soil erosion regions in the world. Two ecological restoration projects, i.e., the integrated soil conservation project since the 1970s and the ''Grain for Green'' project since 1999, have been progressively implemented to control the soil erosion in this area. Ecological restoration has greatly changed flow regime over the past five decades. However, the mechanism of how flow regime responds to ecological restoration among landforms remains poorly understood. In this study, we investigated the temporal dynamics of flow regime in three catchments, i.e., Wuqi, Honghe and Huangling hydrological stations, respectively representing the loess hilly-gully, loess table-gully and rocky mountain (covered by secondary forest) areas in the Chinese Loess Plateau, using daily hydrological data during the 1960s–2010s. The nonparametric Mann-Kendall test, Pettitt's test and daily flow series were used to investigate the changes of flow regime. Significantly negative trends of annual streamflow were detected at the Wuqi and Honghe stations, except for the Huangling station. The annual baseflow at the Wuqi station showed a significantly positive trend whereas a significantly negative trend was observed at the Honghe station, and there was no significant trend at the Huangling station. It was interesting that baseflow index significantly increased during the whole period in all catchments. However, the trends and change points of daily flow series derived by different percentages of exceedance and extreme series in different consecutive days varied among individuals. Based on the change points analysis of annual streamflow, we divided data series into three periods, i.e., the baseline period (from 1959 and 1963 to 1979, PI), the integrated soil conservation period (1980–1999, PII) and the ''Grain for Green'' period (2000–2011, PIII). We found that streamflow decreased due to the reduction of high streamflow (exceeding 5% of time within a year) and median streamflow (50%) in PII and PIII at the Wuqi and Honghe stations. However, low flow (95%) increased in PII and PIII at the Wuqi station while decreased at the Honghe station. Streamflow change at the Huangling station was more stable, thus potentially resulting in much less soil erosion in the forestry area than in the other areas. The great improvement in ecological environment on the Chinese Loess Plateau revealed the advantages of ecological restoration in reducing flood amount and compensating streamflow at a regional scale.

submitted time 2020-05-31 From cooperative journals:《Journal of Arid Land》 Hits9055Downloads1333 Comment 0

2. chinaXiv:202004.00047 [pdf]

Flow regime changes in three catchments with different landforms following ecological restoration in the Chinese Loess Plateau

LUO Zhidong; LIU Erjia; QI Shi; ZHAO Nan; SUN Yun
Subjects: Environmental Sciences, Resource Sciences >> Basic Disciplines of Environmental Science and Technology

The Chinese Loess Plateau is known as one of the most severe soil erosion regions in the world. Two ecological restoration projects, i.e., the integrated soil conservation project since the 1970s and the ''Grain for Green'' project since 1999, have been progressively implemented to control the soil erosion in this area. Ecological restoration has greatly changed flow regime over the past five decades. However, the mechanism of how flow regime responds to ecological restoration among landforms remains poorly understood. In this study, we investigated the temporal dynamics of flow regime in three catchments, i.e., Wuqi, Honghe and Huangling hydrological stations, respectively representing the loess hilly-gully, loess table-gully and rocky mountain (covered by secondary forest) areas in the Chinese Loess Plateau, using daily hydrological data during the 1960s–2010s. The nonparametric Mann-Kendall test, Pettitt's test and daily flow series were used to investigate the changes of flow regime. Significantly negative trends of annual streamflow were detected at the Wuqi and Honghe stations, except for the Huangling station. The annual baseflow at the Wuqi station showed a significantly positive trend whereas a significantly negative trend was observed at the Honghe station, and there was no significant trend at the Huangling station. It was interesting that baseflow index significantly increased during the whole period in all catchments. However, the trends and change points of daily flow series derived by different percentages of exceedance and extreme series in different consecutive days varied among individuals. Based on the change points analysis of annual streamflow, we divided data series into three periods, i.e., the baseline period (from 1959 and 1963 to 1979, PI), the integrated soil conservation period (1980–1999, PII) and the ''Grain for Green'' period (2000–2011, PIII). We found that streamflow decreased due to the reduction of high streamflow (exceeding 5% of time within a year) and median streamflow (50%) in PII and PIII at the Wuqi and Honghe stations. However, low flow (95%) increased in PII and PIII at the Wuqi station while decreased at the Honghe station. Streamflow change at the Huangling station was more stable, thus potentially resulting in much less soil erosion in the forestry area than in the other areas. The great improvement in ecological environment on the Chinese Loess Plateau revealed the advantages of ecological restoration in reducing flood amount and compensating streamflow at a regional scale.

submitted time 2020-04-23 From cooperative journals:《Journal of Arid Land》 Hits1375Downloads743 Comment 0

3. chinaXiv:201904.00096 [pdf]

Strengthened change point detection model for weak mean difference data

Zhou, Qi; Huang, Shaoqian
Subjects: Statistics >> Applied Statistical Mathematics

Objective: The lifetime difference in adjacent parallel structure components becomes small as the number of components belonging to the same parallel structure increases. To infer the system structure, we must clarify the components that belong to the same parallel structure. Methods: A strengthened change point detection model (SCPDM) for weak mean difference data (WMDD) is established, which usually indicates that, as affected by a large variance, the mean difference in two subsignals for one data sequence becomes nonsignificant. For repeatedly retrievable WMDD, we performed two enhanced operations that doubled the mean difference by using the variance information and analyzed the asymptotic properties of the enhanced data. Then, we proposed an SCPDM based on the asymptotic results.Results: Finally, we compared the SCPDM with two other main change point detection models and verified that the SCPDM is superior to other models using WMDD change point detection by the simulation method.Limitations: This paper also have several limitations. First, we only discussed that are independent with normal distribution and single change point. Second, the reason why the relationship between and has an important influence on the accuracy of change point detection is not discussed in depth. We only defined the ratio boundary of WMDD by experience and simulation. Conclusions: Traditional change point detection models may become insensitive or ineffective for WMDD. We gave some asymptotic analysis and established a enhanced change point detection model (SCPDM) based on the asymptotic results. Compared with the traditional method, SCPDM can effectively detect the change point.

submitted time 2019-04-22 Hits19895Downloads2016 Comment 0

  [1 Pages/ 3 Totals]