Simin Qu

Spatial Distribution and Temporal Trends in Precipitation Concentration Indices for the Southwest China

Changes in the spatiotemporal patterns of precipitation have great impacts on drought/flood risk and utilization of water resources. In this study, we presented the results of a comparative analysis of spatial-temporal variability of precipitation in the Southwest China. The analysis investigated the trends of annual precipitation and explored the changes of two indices: the precipitation concentration index (PCI) and the concentration index (CI) which are designed for measuring seasonality and daily heterogeneity, respectively. The trends of annual precipitation and CI were tested by the Mann-Kendall method. The results show a significant seasonality of the rainfall distribution and very inhomogeneous temporal distribution of the daily rainfall in the study area. Positive trends in the CI were found at most stations, although most of them were not statistically significant. To detect the futures trends of precipitation in the study area, Hurst’s rescaled range (R/S) analysis was introduced and the corresponding Hurst Exponent was estimated. The results suggested that some drought hazards will happen in the intersection of Sichuan, Guizhou and Yunnan, and the west part of Sichuan, the north part of Chongqing and the middle part of Yunnan are under the risk of flood in the future.

Regional Frequency Analysis of Low Flow Based on L Moments: Case Study in Karst Area, Southwest China

Regional frequency analysis based on L moments has been used to analyze low flow in the karst area of southwest China. The 7-day low flow was regarded as the statistical quantity. Data from 12 stream flow gauging sites of the Wujiang water system in Guizhou Province are screened using the discordancy measure, and homogeneity of the region is then tested employing the L-moments-based heterogeneity measure. For computing heterogeneity measure H , 500 simulations are performed using the kappa distribution. Based on this test, it is observed that these 12 gauging sites constitute a homogeneous region. Based on the L-moments ratio diagram, | ZDIST | and t4 statistic criteria, generalized logistic (GLO) distribution is identified as the robust distribution for the study area. Regional low flow frequency relationships are developed for estimation of low flow of various return periods for 12 gauged catchments using the GLO distribution and index flood method. Examination of the observed and computed low flow show...

Application of a SWAT Model for Hydrological Modeling in the Xixian Watershed, China

AbstractWater scarcity in Huaihe River, the sixth largest river in China, is stressed by the changing climate and intense human activities, especially in the headwater area. Xixian, situated in the upper reaches of the Huai River, is an important agricultural county with a population of more than one million people, and nearly one billion kg of crop yield every year. The projected climate changes and increasing population are expected to further complicate the utilization of already stressed water resources, endangering the agricultural activities in this area. There is pressing need for a watershed model to better understand the interaction between land use activities and hydrologic processes and to support sustainable water use. This study evaluated the performance of the Soil and Water Assessment Tool (SWAT) for hydrologic modeling in the Xixian basin; three methods of calibration and uncertainty analysis (sequential uncertainty fitting, generalized likelihood uncertainty estimation, and parameter solu...

Analysis of Variation Trends in Precipitation in an Upstream Catchment of Huai River

We analyzed the variation trends in precipitation according to the observed data in the Shaying River catchment, upstream of the Huai River from 1951 to 2010, using the linear regression method and Mann-Kendall test. Further study was made by introducing R/S analysis, and the corresponding Hurst Exponent was estimated to predict the future trends of rainfall. The results suggested that the changing trends in precipitation for different time series in the whole catchment were relatively complex and not obvious. The annual precipitation showed a slightly increasing trend over the past 60 years, and in the future it would be antipersistent. For the 38 rainfall stations, the trends in spring and autumn precipitation time series were mostly negative; on the contrary, the trends in summer and winter were mostly positive. The results also indicated that the annual precipitation series showed positive trends in the northern region and negative trends in the southern region. Moreover, the relationships of H-Z and H-β of the 38 stations were analyzed. The results indicated that the greater the absolute values of Z the stronger the persistent nature. Meanwhile, for most of the H values were close to 0.5, the randomness of the future trends could not be ignored.

Real-Time Equivalent Conversion Correction on River Stage Forecasting with Manning’s Formula

Channel geometry can affect the performance of the autoregressive (AR) model on river stage correction. To evaluate the effect, three ideal models were established by using the one-dimensional (1D) hydrodynamic model with imagined sets of data in assumed channels (i.e., rectangle, V-type, and complex type). To evaluate the performance of the AR model on river stage and discharge correction in a real system with unavailable observed discharges, an equivalent conversion technique by using the Manning’s formula was proposed to convert stages into equivalent conversion discharges. The results from the ideal models and real systems in the Fuchun River show that the AR model performs better on river discharge correction than on river stage correction, which is also verified at Shaowu station in the Minjiang River with available observed discharges. It indicates that the correlation of discharges is better than that of river stages. To transform corrected discharges to corrected stages, a transformation techniqu...

Differences in oxygen-18 and deuterium content of throughfall and rainfall during different flood events in a small headwater watershed

Inter-storm stable isotopic values of rainfall and throughfall for three flooding events were measured during the period of July to August 2011 to estimate their differences in a first-order chestnut watershed, Meilin, within the Taihu Lake basin. Comparison of δ2H and δ18O was conducted from four aspects: (1) sampling methods, (2) calculation methods, (3) stable isotopes and (4) flood events. Arithmetic and weighted incremental values of throughfall were generally lighter than those of rainfall. Isotopic composition of both incremental rainfall and throughfall exhibits marked temporal variation, particularly during large storm events; the former shows a higher variation than the latter. Differences of averaged precipitation and throughfall between storms were small, but individual storm variations were larger. Isotopic differences using different calculation methods are not significant; however, the differences resulting from sampling methods are of greater importance.

The Spatiotemporal Variations of Runoff in the Yangtze River Basin under Climate Change

A better understanding of the runoff variations contributes to a better utilization of water resources and water conservancy planning. In this paper, we analyzed the runoff changes in the Yangtze River Basin (YRB) including the spatiotemporal characteristics of intra-annual variation, the trend, the mutation point, and the period of annual runoff using various statistical methods. We also investigated how changes in the precipitation and temperature could impact on runoff. We found that the intra-annual runoff shows a decreasing trend from 1954 to 2008 and from upper stream to lower stream. On the annual runoff sequence, the upstream runoff has a high consistency and shows an increasing diversity from upper stream to lower stream. The mutation points of the annual runoff in the YRB are years 1961 and 2004. Annual runoff presents multitime scales for dry and abundance changes. Hurst values show that the runoffs at the main control stations all have Hurst phenomenon (the persistence of annual runoff). The sensitivity analyses of runoff variation to precipitation and temperature were also conducted. Our results show that the response of runoff to precipitation is more sensitive than that to temperature. The response of runoff to temperature is only one-third of the response to precipitation. A decrease in temperature may offset the impact of decreasing rainfall on runoff, while an increase in both rainfall and temperature leads to strongest runoff variations in the YRB.

Temporal 18O and deuterium variations in hydrologic components of a small watershed during a typhoon event

ABSTRACT The differences between δ18O and δ2H in throughfall and open rainfall were studied for a selected typhoon event in a watershed within the Taihu Lake drainage basin, eastern China. In this event, the isotopic composition of precipitation exhibited a strong temporal variation. Comparison results show that an isotopic composition difference existed not only between gross rainfall and average incremental rainfall, but also between different calculation methods used to derive average. The differences between incremental precipitation and throughfall isotopic composition were observed in this study. Considering the temporal variation in rainfall and throughfall during this typhoon event, the incremental value can have an effect on hydrograph separation more accurately in evaluating the importance of ‘new’ water. In addition, isotopic fluctuations of surface water and groundwater differed from those of rainfall and throughfall throughout the event.