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The spatial and temporal trends of 11 (7) temperature (precipitation) extreme indices are examined for the Loess Plateau Region (LPR) and its southeast and northwest sub-regions based on daily observations at 214 meteorological stations. Results show widespread significant warming trends for all the temperature extremes except for the diurnal temperature range (DTR) and the lowest daily maximum temperature in each year (TXn) during 1961-2010. When regionally averaged, a significant warming trend is detected for all the indices except for DTR and TXn in the past 50 years. Compared with the entire LPR, a significant warming trend is detected for all the indices except for DTR and TXn over the southeast sub-region of LPR; while it is observed for all the indices over the northwest. The trends for these indices are generally stronger in the northwest than in the southeast in the past 50 years. In contrast, for precipitation indices, only a small percentage of areas show significant drying or wetting trends and, when regionally averaged, none of them displays significant trends during the past 50 years. On the sub-regional scale, however, a larger percentage of areas show significant drying trends for precipitation indices generally over the southeast relative to the entire LPR, and noticeably, the sub-regional average heavy precipitation (R10mm) and wet day precipitation (PRCPTOT) display significant decreasing trends during the past 50 years; whereas only a slightly larger percentage of areas show significant wetting trends for these indices over the northwest compared with the entire LPR, and when sub-regionally averaged, none of the indices have significant trends during the past 50 years. [ABSTRACT FROM AUTHOR]

Summary: An empirical power function model of V = kQm has been used worldwide to describe the relationship between flow velocity (V, ms−1) and discharge rate (Q, m3 s−1) for rill and open channel flows. However, it has seldom been applied to watershed outlet channels taking into account the impacts of watershed size. In this study, observed data from four experimental watersheds of different sizes, ranging from about 1 to 100km2, were used to verify the stability of the power function model for use at a watershed level on the Loess Plateau. An alternative logarithmic function model of was also tested. Results showed that the constant parameters in both model types were impacted by watershed size, which are inherently directly related to the size of the outlet channels. The constants k and d, which represent flow velocity for unit discharge rate, were negatively correlated with watershed size. However, the exponential constants m and e, which determine the rate of change in flow velocity with respect to discharge rate, were shown to be independent of watershed size. Furthermore, soil and water conservation land use management on the Loess Plateau was also shown to indirectly affect the flow velocity–discharge rate relationship in the smallest watersheds (1km2). The study indicated that, although the performance of the logarithmic function model was acceptable, the power function model generally performed better over a larger range of flow velocity values and was better able to represent the flow velocity–discharge rate relationship in the unique context of the Loess Plateau. [Copyright &y& Elsevier]