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次降雨时空分布对流域产流产沙的影响

Effects of the spatio-temporal pattern of single storm on the runoff and sediment yield at watershed scale

  • 摘要: 降雨时空变异性对流域产流产沙过程具有重要影响。选取数据完整性较好、分辨率较高的美国俄克拉荷马州柯尔堡(Fort Cobb)流域为研究对象,基于高时空分辨率次降雨空间分布及移动特征的量化分析,探究降雨雨型、降雨强度、时空变异等对流域产流产沙过程的影响。结果表明:依据降雨特征(降雨量、降雨历时,30 min最大降雨强度)可将Fort Cobb流域的雨型划分为4类(A型、B型、C型和D型),其中,降雨量和30 min最大降雨强度较小的A型、B型降雨最为常见;C型降雨的30 min最大降雨强度最大,是造成该流域水土流失的主要类型。对于4种雨型,流域产流量与降雨量,产沙量与次降雨侵蚀力皆呈显著正相关关系(P<0.05);单位降雨量导致的流域产流量表现为C型>A型>D型>B型;相同次降雨侵蚀力条件下,不同雨型导致的流域产沙量则表现为D型>B型>A型>C型。流域降雨量空间分布呈现由东南向西北减少的趋势,集中分布在流域东部的降雨量占总降雨量38.96%。降雨移动特征分析表明,流域内向下游移动和顺时针移动的降雨场次最多,发生频次为51.16%,2类降雨量占总量的57.94%,其导致的流域产流量占总量的81.61%,产沙量占总量的84.84%。降雨过程相似时,次降雨移动特征对流域产流产沙作用存在明显差异。降雨由上游至下游移动,流域水文响应速度慢,流量、含沙量峰值高;而降雨由下游至上游移动,流域水文响应速度快,且流量、含沙量峰值较低。

     

    Abstract:
    Background There are many factors affecting the hydrological response at watershed scale. In recent years, more and more studies have been conducted on the effects of spatio-temporal patterns of storm on hydrological response. Most of these studies are based on mathematical models because of the scarcity of high-resolution data. Many research indicated that spatio-temporal patterns of storm events play an important role in runoff discharge and sediment yield at watershed scale. Due to the good data integrity and high resolution, the Fort Cobb watershed in Oklahoma state, USA, was selected as the research site.
    Methods Based on high-resolution meteorological and hydrological data, this study quantified and traced the storm path and spatial distribution of 43 storms in Fort Cobb watershed by using K-means clustering method and Kriging interpolation method. And the effects of storm pattern, rainfall intensity and spatio-temporal characteristics on runoff discharge and sediment yield of Fort Cobb watershed were studied.
    Results 1) The 43 storm events were classified into 4 patterns. Type A, with small rainfall, variable rainfall duration and medium maximum 30-min rainfall intensity. Type B, with small rainfall, variable rainfall duration and small maximum 30-min rainfall intensity. Type C, with medium rainfall, short rainfall duration and medium maximum 30-min rainfall intensity. Type D, with large rainfall, short rainfall duration, and medium maximum 30-min rainfall intensity. Storms with small rainfall and low maximum 30-min rainfall intensity were the commonest pattern. Type C was the main pattern that caused soil erosion in the research area. 2) The runoff discharge and sediment yield were significantly and positively correlated with rainfall and rainfall erosivity (P < 0.05) even if under different storm patterns (P < 0.05). When the rainfall was the same, different types of storms leads to runoff as C>A>D>B. When the value of rainfall erosivity was equal, different types of storms caused different sediment yield in this area, and the amount from the highest to the lowest was D>B>A>C. 3) The spatial difference of storms was relatively huge. The rainfall was much more in the east and the south than that in the west and the north. The rainfall in the northeast and the southeast accounted for 38.96% of the total. 4) The storms moving downstream and clockwise accounted for the most amount of rainfall of 57.94% and 81.61% runoff discharge and 84.84% sediment yield. Most of storms started from the northwest of the basin and moved downstream. When the process of rainfall was similar, the storm moving upstream had a fast hydrological response and a low peak flow and sediment yield. On the contrary, the storm moving downstream had a slow hydrological response and a high runoff and sediment yield.
    Conclusions The spatial and temporal distribution characteristics of storms have impact on the hydrological response of watershed, which is significantly reflected in the hydrological process and sediment yield. This result may provide a basis for understanding the complex interactions between rainfall variability and catchment heterogeneity.

     

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