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This study aims to investigate trends in streamflow and precipitation in the period 1954–2010 in a semiarid region of the Yellow River watershed, Huangfuchuan basin, China. The combination of the wavelet transform and different Mann-Kendall (MK) tests were employed to figure out the basic trends structure in streamflow and precipitation and what time scales are affecting the observed trends. The comparative analysis with five MK test methods showed that the modified MK tests with full serial correlation structure performed better when significant autocorrelations exhibited for more than one lag. Three criteria were used to determine the optimal smooth mother wavelet, the decomposition level and the extension mode used in the discrete wavelet transform (DWT) procedure. The first criteria referred to the relative error of the wavelet approximated component and the original series. The second one was the relative error of MK Z-values of approximation component and the original series. Additionally, a new criterion (Er), based on the relative error of energy between the approximate component and the original series, was proposed in this study, with better performance than the previous two criteria. Further, a new powerful index, the energy of the hydrological time series, was proposed to verify the dominant periodic components for the observed trends. The analysis indicated that all monthly, seasonal and annual streamflow showed significant decreasing trends, while no significant trends were found in precipitation. Results from the DWT and MK tests revealed that the main factors influencing the trends in the monthly and seasonal series in Huangfuchuan watershed are intra-annual cycles, while the leading factors affecting the trends in the annual series are decadal events. Different driving factors (e.g., seasonal cycles, solar activities, etc.) related to the periodicities identified in these data types resulted in this discrepancy. [ABSTRACT FROM AUTHOR]

Soil erosion, more than any other factor, has more significant and direct impacts on a hydrological watershed in terms of environmental problems. After deriving the erosion hotspots, this study used them to investigate two watersheds, Hocking River Basin and Atwood Lake Basin, in Ohio. Each watershed was divided into 30 × 30m grids, respectively, using the geographic information system (GIS), while the revised universal soil loss equation (RUSLE) was applied to estimate the soil erosion for each grid. Grid values of soil erosion estimates are ranked numerically from the lowest to the highest. Grids of soil erosion estimates equal to or greater than the top 5% value are defined as erosion hotspots to form the erosion hotspot image. Then, assigning individual parameters of land slope, soil type, and land use to be 1, to neutralize individual effects in the RUSLE modeling, three different erosion hotspot images were derived in a similar manner. Overlaying each of these three erosion hotspot images with the original erosion hotspot image, it was found that the land slope factor as a representative topography of the watershed has the most significant effect on erosion hotspots for both watersheds compared with soil types and land uses. Generally, the erosion estimate increases as the land slope increases, but the combination of soil type factor with land slope factor results in more effects on erosion hotspots in the Hocking River Basin than their counterparts in the Atwood Lake Basin. On the other hand, the combination of the land use factor with land slope factor has more effects on erosion hotspots in the Atwood Lake Basin than in the Hocking River Basin. [ABSTRACT FROM AUTHOR]

The impact of the El Niño-Southern Oscillation (ENSO) phenomenon within the Huangfuchuan watershed, one of the major first-order sub-basins in the middle region of the Yellow River, has not clearly been established. Consequently, the co-varying relationships between rainfall and El Niño/La Niña spanning the period 1954 to 2010 are investigated. Trends and step changes in annual rainfall are investigated with the Mann-Kendall and the distribution free cumulative sum (CUSUM) tests. Wavelet transforms are employed to perform spectral analysis of temporal variations in rainfall rates within the watershed. Cross wavelet and wavelet coherence transforms are used to study localized co-varying relationships between rainfall and ENSO index. Results from statistical tests indicate that rainfall in the Huangfuchuan watershed is declining, although not significantly. In addition, wavelet coherency and cross wavelet analysis, and comparison of the extracted dominant annual rainfall and 2-7 year ENSO signals demonstrate that ENSO events impact Huangfuchuan rainfall with El Niño corresponding to rainfall decline and La Niña to rainfall increment with a semiannual to annual lag. [ABSTRACT FROM AUTHOR]