Improved Runoff Simulations for a Highly Varying Soil Depth and Complex Terrain Watershed in the Loess Plateau with the Community Land Model

Abstract. This study aimed to improve runoff simulations and explore deep soil hydrological processes for a watershed in the center of the Loess Plateau (LP), China. This watershed, the Wuding River Basin (WRB), has very complex topography, with soil depths ranging from 0 to 197 m. The hydrological model used for our simulations was the Community Land Model (CLM) version 5 developed by the National Center for Atmospheric Research. Actual soil depths and river channels were incorporated into CLM to realistically represent the physical features of the WRB. Through sensitivity tests, CLM with 150 soil layers produced the most reasonable results and was adopted for this study. Our results showed that CLM with actual soil depths significantly suppressed unrealistic variations of the simulated sub-surface runoff when compared to the default simulations with a fixed soil depth of 8 m. In addition, CLM with higher-resolution soil layering slightly improved runoff simulations, but generated simulations with much smoother vertical water flows that were consistent with the uniform distribution of soil textures in our study watershed. The runoff simulations were further improved by the addition of river channels to CLM, where the seasonal variability of the simulated runoff was reasonably captured. Moreover, the magnitude of the simulated runoff remarkably decreased with increased soil evaporation by lowering the soil water content threshold, which triggers surface resistance. The lowered threshold was consistent with the loess soil, which has a high sand component. Such soils often generate stronger soil evaporation than soils dominated by clay. Finally, with the above changes in CLM, the simulated total runoff matched very closely with observations. When compared with those for the default runoff simulations, the correlation coefficient, root-mean-square error, and Nash Sutcliffe coefficient for the improved simulations changed dramatically from 0.02, 10.37 mm, and −12.34 to 0.62, 1.8 mm, and 0.61. The results in this study provide strong physical insight for further investigation of hydrological processes in complex terrain with deep soils.

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Factors influencing soil moisture in the Loess Plateau, China: a review

Earth and Environmental Science Transactions of the Royal Society of Edinburgh ◽

10.1017/s1755691018000671 ◽

2018 ◽

Vol 109 (3-4) ◽

pp. 501-509

Author(s):

Wenwu ZHAO ◽

Xuening FANG ◽

Stefani DARYANTO ◽

Xiao ZHANG ◽

Yaping WANG

Keyword(s):

Soil Moisture ◽

Loess Plateau ◽

Arid Regions ◽

Scale Effects ◽

Soil Depth ◽

Three Dimensional ◽

Future Research ◽

The Loess Plateau ◽

Deep Soil ◽

Semi Arid

ABSTRACTSoil moisture is a key issue for eco-hydrological research in arid and semi-arid regions, and is primarily concerned with water availability for vegetation. Shallow and deep soil moisture occurs according to the maximum infiltration depth. Soil moisture has three-dimensional characteristics: inter-layer variability, horizontal heterogeneity and temporal variability. Soil moisture is affected by various factors including terrain, soil characteristics, climate and vegetation, and the effects of these change with time (e.g., rainfall patterns) and space (e.g., soil depth). In arid and semi-arid regions, deep soil moisture is of particular importance to vegetation restoration and the evaluation of vegetation sustainability; however, accurate prediction of the spatial distribution of deep soil moisture in the Loess Plateau of China still faces numerous challenges. Therefore, future research should focus on the mechanisms, models and scale effects of soil moisture, particularly for deep soil moisture.

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Quantifying the Responses of Evapotranspiration and Its Components to Vegetation Restoration and Climate Change on the Loess Plateau of China

Remote Sensing ◽

10.3390/rs13122358 ◽

2021 ◽

Vol 13 (12) ◽

pp. 2358

Author(s):

Linjing Qiu ◽

Yiping Wu ◽

Zhaoyang Shi ◽

Yuting Chen ◽

Fubo Zhao

Keyword(s):

Climate Change ◽

Loess Plateau ◽

Dominant Role ◽

Vegetation Restoration ◽

Vegetation Coverage ◽

Ecological Planning ◽

The Loess Plateau ◽

Canopy Interception ◽

Community Land Model ◽

Spatiotemporal Trends

Quantitatively identifying the influences of vegetation restoration (VR) on water resources is crucial to ecological planning. Although vegetation coverage has improved on the Loess Plateau (LP) of China since the implementation of VR policy, the way vegetation dynamics influences regional evapotranspiration (ET) remains controversial. In this study, we first investigate long-term spatiotemporal trends of total ET (TET) components, including ground evaporation (GE) and canopy ET (CET, sum of canopy interception and canopy transpiration) based on the GLEAM-ET dataset. The ET changes are attributed to VR on the LP from 2000 to 2015 and these results are quantitatively evaluated here using the Community Land Model (CLM). Finally, the relative contributions of VR and climate change to ET are identified by combining climate scenarios and VR scenarios. The results show that the positive effect of VR on CET is offset by the negative effect of VR on GE, which results in a weak variation in TET at an annual scale and an increased TET is only shown in summer. Regardless of the representative concentration pathway (RCP4.5 or RCP8.5), differences resulted from the responses of TET to different vegetation conditions ranging from −3.7 to −1.2 mm, while climate change from RCP4.5 to RCP8.5 caused an increase in TET ranging from 0.1 to 65.3 mm. These findings imply that climate change might play a dominant role in ET variability on the LP, and this work emphasizes the importance of comprehensively considering the interactions among climate factors to assess the relative contributions of VR and climate change to ET.

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Vertical distribution of soil available phosphorus and soil available potassium in the critical zone on the Loess Plateau, China

Scientific Reports ◽

10.1038/s41598-021-82677-4 ◽

2021 ◽

Vol 11 (1) ◽

Cited By ~ 1

Author(s):

Hanyang Tian ◽

Jiangbo Qiao ◽

Yuanjun Zhu ◽

Xiaoxu Jia ◽

Ming’an Shao

Keyword(s):

Vertical Distribution ◽

Loess Plateau ◽

Clay Content ◽

Exponential Model ◽

Critical Zone ◽

Available Phosphorus ◽

Soil Core ◽

The Loess Plateau ◽

Deep Soil ◽

Soil Available Phosphorus

AbstractSoil available phosphorus (SAP) and soil available potassium (SAK) are important elements in the growth of plants. However, limited data are available regarding the vertical distribution of SAP and SAK in deep soil profiles. In this study, we investigated the vertical variations in SAP and SAK in the critical zone on the Loess Plateau (50–200 m), China, by using classical statistical and geostatistical methods. The soil samples were collected from the top of the soil profile down to the bedrock by soil core drilling at five typical sites. SAP decreased throughout the profile. Whereas the SAK exhibited an increasing trend at all sites. The mean SAP concentration ranged from 0.94 to 32.56 mg kg–1 at the sampling sites and the SAK concentration ranged from 44.51 to 229.31 mg kg–1. At all of the sampling sites, SAK was significantly positively correlated with the depth and clay content, but there was a significantly negative correlation between the SAK and the sand content. The exponential model could fit most variograms of SAP and SAK at all sampling sites. The results obtained in this study to improve our comprehension of the SAP or SAK distribution conditions on the Loess Plateau, which is important for reasonable fertilizer application and vegetation planting practices.

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Effects of deep soil desiccation on artificial forestlands in different vegetation zones on the Loess Plateau of China

Acta Ecologica Sinica ◽

10.1016/s1872-2032(08)60052-9 ◽

2008 ◽

Vol 28 (4) ◽

pp. 1429-1445 ◽

Cited By ~ 48

Author(s):

Li Jun ◽

Chen Bing ◽

Li Xiaofang ◽

Zhao Yujuan ◽

Ciren Yangjing ◽

...

Keyword(s):

Loess Plateau ◽

The Loess Plateau ◽

Deep Soil ◽

Soil Desiccation ◽

Vegetation Zones

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Quantify Piston and Preferential Water Flow in Deep Soil Using Cl− and Soil Water Profiles in Deforested Apple Orchards on the Loess Plateau, China

Water ◽

10.3390/w11102183 ◽

2019 ◽

Vol 11 (10) ◽

pp. 2183 ◽

Cited By ~ 1

Author(s):

Zhiqiang Zhang ◽

Bingcheng Si ◽

Huijie Li ◽

Min Li

Keyword(s):

Soil Water ◽

Water Flow ◽

Loess Plateau ◽

Preferential Flow ◽

Chloride Ions ◽

Apple Orchards ◽

The Loess Plateau ◽

Deep Soil ◽

Soil Water Profiles ◽

Preferential Water

Piston and preferential water flow are viewed as the two dominant water transport mechanisms regulating terrestrial water and solute cycles. However, it is difficult to accurately separate the two water flow patterns because preferential flow is not easy to capture directly in field environments. In this study, we take advantage of the afforestation induced desiccated deep soil, and directly quantify piston and preferential water flow using chloride ions (Cl−) and soil water profiles, in four deforested apple orchards on the Loess Plateau. The deforestation time ranged from 3 to 15 years. In each of the four selected orchards, there was a standing orchard that was planted at the same time as the deforested one, and therefore the standing orchard was used to benchmark the initial Cl− and soil water profiles of the deforested orchard. In the deforested orchards, piston flow was detected using the migration of the Cl− front, and preferential flow was measured via soil water increase below the Cl− front. Results showed that in the desiccated zone, Cl− migrated to deeper soil after deforestation, indicating that the desiccated soil layer formed by the water absorption of deep-rooted apple trees did not completely inhibit the movement of water. Moreover, there was an evident increase in soil water below the downward Cl− front, directly demonstrating the existence of preferential flow in deep soil under field conditions. Although pore water velocity was small in the deep loess, preferential water flow still accounted for 34–65% of total infiltrated water. This study presented the mechanisms that regulate movement of soil water following deforestation through field observations and advanced our understanding of the soil hydrologic process in deep soil.

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Simulating the Hydrological Processes of a Meso-Scale Watershed on the Loess Plateau, China

Water ◽

10.3390/w12030878 ◽

2020 ◽

Vol 12 (3) ◽

pp. 878 ◽

Cited By ~ 1

Author(s):

Manman Leng ◽

Yang Yu ◽

Shengping Wang ◽

Zhiqiang Zhang

Keyword(s):

Land Use ◽

Sensitivity Analysis ◽

Loess Plateau ◽

Swat Model ◽

Hydrological Processes ◽

P Value ◽

Runoff Generation ◽

The Loess Plateau ◽

Monthly Streamflow ◽

Meso Scale

The Soil and Water Assessment Tool (SWAT) model is widely used to simulate watershed streamflow by integrating complex interactions between climate, geography, soil, vegetation, land use/land cover and other human activities. Although there have been many studies involving sensitivity analysis, uncertainty fitting, and performance evaluation of SWAT model all over the world, identifying dominant parameters and confirming actual hydrological processes still remain essential for studying the effect of climate and land use change on the hydrological regime in some water-limited regions. We used hydro-climate and spatial geographical data of a watershed with an area of 3919 km2, located on the Loess Plateau of China, to explore the suitable criterion to select parameters for running the model, and to elucidate the dominant ones that govern the hydrological processes for achieving the sound streamflow simulation. Our sensitivity analysis results showed that parameters not passing the sensitive check (p-value < 0.05) could play a significant role in hydrological simulation rather than only the parameters with p-value lower than 0.05, indicating that the common protocol is not appropriate for selecting parameters by sensitivity screening only. Superior performance of the rarely used parameter SOL_BD was likely caused by a combination of lateral and vertical movement of water in the loess soils due to the run-on infiltration process that occurred for meso-scale watershed monthly streamflow modeling, contrasting with traditionally held infiltration excessive overland flow dominated runoff generation mechanisms that prevail on the Loess Plateau. Overall, the hydrological processes of meso-scale watershed in the region could be well simulated by the model though underestimates of monthly streamflow could occur. Simulated water balance results indicated that the evapotranspiration in the region was the main component leaving the watershed, accounting for 88.9% of annual precipitation. Surface runoff contributed to 63.2% of the streamflow, followed by lateral flow (36.6%) and groundwater (0.2%). Our research highlights the importance for selecting more appropriate parameters for distributed hydrological models, which could help modelers to better comprehend the meso-scale watershed runoff generation mechanism of the Loess Plateau and provide policy makers robust tool for developing sustainable watershed management planning in water-limited regions.

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Earthworm Burrowing Activity and Its Effects on Soil Hydraulic Properties under Different Soil Moisture Conditions from the Loess Plateau, China

Sustainability ◽

10.3390/su12219303 ◽

2020 ◽

Vol 12 (21) ◽

pp. 9303

Author(s):

Shuhai Wen ◽

Ming’an Shao ◽

Jiao Wang

Keyword(s):

Soil Moisture ◽

Loess Plateau ◽

Hydraulic Properties ◽

Soil Depth ◽

Soil Aggregates ◽

Field Capacity ◽

Soil Hydraulic Properties ◽

The Loess Plateau ◽

Burrowing Activity ◽

Soil Hydraulic

Earthworm activity has become more important in the Loess Plateau, where hydrological processes are crucial for ecosystem sustainability. In this study, we conducted a laboratory microcosm experiment to determine the various burrowing activities of Eisenia fetida and their impact on the soil hydraulic properties in response to different levels of soil moisture (50%, 70%, 90% of field capacity) in two common soil types (loessial and Lou soil) obtained from the Loess Plateau. Burrowing activity of E. fetida increased with higher soil moisture and was greater in loessial than in Lou soil. Most burrowing activities occurred within the top 5 cm and decreased with increasing soil depth. Macropores and burrow branching, which are highly related to the earthworm burrowing, were more prevalent in wetter soil. Earthworms significantly altered the formation of large soil aggregates (AGL, diameter >2 mm) under different soil moistures and depths. Distinct earthworm burrowing activities, controlled by soil moisture, altered soil hydraulic properties. However, soil saturated hydraulic conductivity (Ks) showed little differences between different treatments due to the horizontal and high–branched burrows of E. fetida, although higher burrowing activities were found in wetter soil. Soil field capacity was highest in drier soil due to the less macropores and burrowing activities.

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Culturable autotrophic ammonia-oxidizing bacteria population and nitrification potential in a sheep grazing intensity gradient in a grassland on the Loess Plateau of Northwest China

Canadian Journal of Soil Science ◽

10.4141/cjss2010-003 ◽

2011 ◽

Vol 91 (6) ◽

pp. 925-934 ◽

Cited By ~ 5

Author(s):

Tianzeng Liu ◽

Zhibiao Nan ◽

Fujiang Hou

Keyword(s):

Loess Plateau ◽

Soil Depth ◽

Grazing Intensity ◽

Northwest China ◽

Ammonia Oxidizing Bacteria ◽

Stocking Rate ◽

The Loess Plateau ◽

Soil Microbial ◽

Nitrification Potential ◽

Dry Soil

Liu, T., Nan, Z. and Hou, F. 2011. Culturable autotrophic ammonia-oxidizing bacteria population and nitrification potential in a sheep grazing intensity gradient in a grassland on the Loess Plateau of Northwest China. Can. J. Soil Sci. 91: 925–934. Grazing is known to enhance the activity of soil microbial communities in many types of grasslands; however, the potential impacts of rotational grazing activity on soil microbial functional groups remain poorly understood. We investigated the effects of 9 yr of rotational grazing by livestock on culturable autotrophic ammonia-oxidizing bacteria (AOB) population size, nitrification potential and soil properties in a semi-arid grassland of the Loess Plateau in Northwest China. Three stocking rate treatments of 2.7, 5.3 and 8.7 wether lambs ha−1were evaluated in geographically separated paddocks. Grazing increased nitrification potential and culturable AOB populations compared with ungrazed treatments. Ammonia-oxidizing bacteria populations increased from 155 bacteria g−1dry soil with 0 sheep ha−1to 16 218 bacteria g−1dry soil with 8.7 sheep ha−1. Grazing led to an increase in population of AOB at 0–10 cm soil depth, but had no effect on AOB at 10–20 cm soil depth. Nitrification potential increased from 1.21 mg NO3-N kg−1soil d−1in ungrazed treatments to 2.86 mg NO3-N kg−1soil d−1at the highest stocking rate. Soil ammonium and nitrate concentrations increased; however, total soil nitrogen and soil moisture content decreased with increased stocking rate for both sampling depths (0–10 cm and 10–20 cm). Soil organic matter was not affected by grazing treatments. Soil nitrification potential and the size of culturable AOB populations were dependent on grazing intensity, soil depth and season. This information is potentially important for the optimal selection of stocking rate for grazed ecosystems.

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