Integrating water use systems and soil and water conservation measures into a hydrological model of an Iranian Wadi system

Water resources are precious in arid and semi-arid areas such as the Wadis of Iran. To sustainably manage these limited water resources, the residents of the Iranian Wadis have been traditionally using several water use systems(WUSs) which affect natural hydrological processes. In this study, WUSs and soil and water conservation measures(SWCMs) were integrated in a hydrological model of the Halilrood Basin in Iran. The Soil and Water Assessment Tool(SWAT) model was used to simulate the hydrological processes between 1993 and 2009 at daily time scale. To assess the importance of WUSs and SWCMs, we compared a model setup without WUSs and SWCMs(Default model) with a model setup with WUSs and SWCMs(WUS-SWCM model). When compared to the observed daily stream flow, the number of acceptable calibration runs as defined by the performance thresholds(Nash-Sutcliffe efficiency(NSE)≥0.68, –25%≤percent bias(PBIAS)≤25% and ratio of standard deviation(RSR)≤0.56) is 177 for the Default model and 1945 for the WUS-SWCM model. Also, the average Kling–Gupta efficiency(KGE) of acceptable calibration runs for the WUS-SWCM model is higher in both calibration and validation periods. When WUSs and SWCMs are implemented, surface runoff(between 30% and 99%) and water yield(between 0 and 18%) decreased in all sub-basins. Moreover, SWCMs lead to a higher contribution of groundwater flow to the channel and compensate for the extracted water by WUSs from the shallow aquifer. In summary, implementing WUSs and SWCMs in the SWAT model enhances model plausibility significantly.

Comparative Mountain Hydrology: A Case Study of Wis?ok River in Poland and Chaohe River in China

Hydrological processes in river basins of similar size and morphology may differ significantly due to different climatic conditions. This paper presents a comparative analysis of hydrological characteristics of two river basins located in different climatic zones: the Wisok River Basin in the south-eastern Poland and the Chaohe River Basin in the northern China. The criteria of their choice were similarities in the basin area, main river length and topography. The results show that climate plays a key role in shaping fluvial conditions within the two basins. It is concluded that: 1) precipitation in the Wisok River Basin is more evenly distributed in the yearly cycle, while in the Chaohe River Basin it is highly concentrated in the few summer months; 2) spring snowmelt significantly contributes to runoff in the Wisok River Basin, while its role in the Chaohe River Basin is negligible; 3) in the Wisok River Basin, besides the peak flow in spring, there is also a period of high water in summer resulting from precipitation, while in the Chaohe River Basin there is only one high water period in summer; 4) the Wisok River Basin shows relatively higher stability in terms of the magnitude of intra- and inter-seasonal discharges; 5) during the multi-year observation period, a decrease in both precipitation and runoff was recorded in the two river basins.

Comparison of two different methods for determining flow direction in catchment hydrological modeling

Digital elevation models （DEMs） are widely used to define the flow direction in distributed hydrological models for simulation of streamflow. In recent decades, numerous methods for flow direction determination have been applied successfully to mountainous regions. Nevertheless, some problems still exist when those methods are used for flat or gently sloped areas The present study reviews the conventional methods of determining flow direction for such landscapes and analyzes the problems of these methods. Two different methods of determining flow direction are discussed and were applied to the Xitiaoxi Catchment, located in the Taihu Basin in southern China, which has both mountainous and flat terrain. Both the agree method and the shortest path method use drainage networks derived from a remote sensing image to determine the correct location of the stream. The results indicate that the agree method provides a better fit with the DEM for the hilly region than the shortest path method. For the flat region where the flow has been diverted and rerouted by land managers, both methods require observation of the drainage network to determine the flow direction. In order to clarify the applicability of the two methods, both are employed in catchment hydrological models conceptually based on the Xinanjiang model and implemented with PCRaster. The simulation results show that both methods can be successfully applied in hydrological modeling. There are no evident differences in the modeled discharge when using the two methods at different spatial scales.

水文循环模拟中蒸散发估算方法综述

为选取基于水文循环估算蒸散发方法提供依据,首先对常用水文模型中蒸散发估算方法进行回顾,根据其物理机理的强弱性,将水文模型中蒸散估算方法分为整体折算法和分类汇总法。当前水文模型中整体折算法占较大比重,它们之间的差异有两点:一是潜在蒸散发估算方法不同;二是土壤干燥度折算函数不同;研究表明:由于水文模型存在不确定性及Penman-Monteith方法具有较高资料要求,致使模拟中使用该方法与使用其它简化经验公式相似或更差的水文循环模拟效果。所以对于不同水文模型,如何选取与之复杂程度相兼容的潜在蒸散发估算方程和土壤干燥度折算函数来降低模型的不确定性需进一步讨论。在此基础上,预估基于水文循环估算蒸散发方法朝着复杂机理化和简单实用化两个方向发展。

Using high-resolution aerial images to study gully development at the regional scale in southern China

There are 239,100 gullies in southern China,which cause the degradation of ecological system.However,studies on gully development at the regional scale is relatively lack.The purpose of this study is to analyze the regional gully dynamics and explore how land use and topographic factors affect gully development.Input data consists of land use maps derived from high-resolution images from 2004 to 2014,and topography maps from a digital elevation model with a pixel size of 8 m×8 m in two 25-km2 study sites of Anxi(AX)and Xingning county(XN).The following results were obtained:(1)AX gullies decreased from 2006 to 2014 while XN first increased from 2004 to 2009,and then decreased from 2009 to 2014.Both AX and XN gully area in percentage of the total area ranged from 1%to 3%,which was higher than the average 0.25%of the whole southern China by the artificial survey in 2005.(2)Most of AX and XN gullies occurred along the ridgeline and had the close relationships with the upstream contributing area and slope gradient.(3)New gullies developed on the exposed land and forestland.The lost gullies were converted into forestland and grassland.In fact,most of these gullies were only covered by vegetation,not real disappearance.These results proved that gully decreased,but construction of roads and buildings intensified gully development.Consequently,these findings reveal that vegetation protection and ecological restoration should be adopted in southern China.