The Seasonal Water Balance of Western-Juniper-Dominated and Big-Sagebrush-Dominated Watersheds

The combined impacts of woody plant encroachment and climate variability have the potential to alter the water balance in many sagebrush steppe ecosystems in the Western USA, leading to reduced water availability in these already water-scarce regions. This study compared the water-balance characteristics of two adjacent semiarid watersheds in central Oregon, USA: one dominated by big sagebrush and one dominated by western juniper. Precipitation, springflow, streamflow, shallow groundwater levels, and soil moisture were measured. The potential evapotranspiration was calculated using the Hargreaves–Samani method. Potential evapotranspiration and a water-balance approach were used to calculate seasonal actual evapotranspiration. The shallow aquifer recharge was calculated using the Water-Table-Fluctuation-Method. Evapotranspiration, followed by deep percolation, accounted for the largest portion (83% to 86% of annual precipitation) of water output for both watersheds. Springflow and streamflow rates were generally greater at the sagebrush-dominated watershed. Snow-dominated years showed greater amounts of groundwater recharge and deep percolation than years where a larger portion of precipitation fell as rain, even when total annual precipitation amounts were similar. This study’s results highlight the role of vegetation dynamics, such as juniper encroachment, and seasonal precipitation characteristics, on water availability in semiarid rangeland ecosystems.

Evaluating performance of soil water movement and groundwater recharge in an irrigated agricultural area of Yinchuan Plain, China

Surface irrigation has been predominantly used for field crops in agriculture area to boost agricultural yields and outputs, however, this may also raise groundwater tables, salinize soils and reduce water quality due to poor irrigation management. Therefore, it is essential for requiring a better understanding of the hydrologic mechanisms related to soil water fluxes (e.g., evaporation, transpiration, infiltration, deep percolation and groundwater capillary rise) by surface irrigation. This study investigated the impact of surface irrigation on soil water movement and recharge to groundwater in the Yellow River irrigation area of Yinchuan Plain, China. Combining comprehensive filed observation and stable isotopic techniques, we described the soil water mechanism under two land covers (bare ground or maize) in 2019 and 2020. The soil depths affected by precipitation infiltration and evaporation were mainly 0-50 cm, while the soil influenced by irrigation was the entire profile in the mode of piston flow. According to soil water potential variation from 70 to 100 cm, we conclude that the maize root took up the soil water up to the depth of 100 cm during the tasseling period. The infiltration and capillary rise in 2020 were similar with those in 2019. However, the total deep percolation was 156.6 mm in 2020 which was smaller than that in 2019 because of the maize root water uptake. The leakage of ditch was the major recharge resource of groundwater for the fast water table rise. This study is critical for agricultural water management to improve irrigation efficiency and water use efficiency in arid regions.

Modeling the Effect of Different Forest Types on Water Balance in the Three Gorges Reservoir Area in China, with CoupModel

Precipitation, throughfall, stemflow, and soil water content were measured, whereas interception, transpiration, evaporation, deep percolation, and soil water recharge were estimated in three plots, including oak (Lithocarpus glaber), Chinese fir (Cunninghamia lanceolata) forestlands, and maize (Zea mays) farmland in the Three Gorges Reservoir in China. A physical process-based model (CoupModel) was set up with climatic measurements as input and was calibrated with throughfall and vertical frequency domain reflectometry measurements from January 2018 to December 2019. Simulated values of soil moisture were fairly consistent with measured ones, with a determination coefficient (R2) of 0.73–0.91. Evapotranspiration was the main output of water balance, with a percentage of up to 61%, and such output was ranked as follows: oak forest (720 mm/y) > Chinese fir forest (700 mm/y) > maize farmland (600 mm/y). Afforestation influenced water balance, and water recharge was generally less significant in oak forestland than in Chinese fir forestland. Annual simulated deep percolation decreased by 60 mm for oak and 47 mm for Chinese fir compared with that for farmland (452 mm/y) and even more significantly in wet years. This decrease was mainly attributed to increased interception (122–159 mm/y) and transpiration (49–84 mm/y) after afforestation. Simulations indicated that vegetation species significantly influenced the magnitude of water balance components, calling for further attention to the selection of regrown tree species in the planning for afforestation projects, particularly for such projects that aim to improve the quantity of water infiltrating groundwater. Soil and water conservation measures should also be applied scientifically when converting farmland to forest in this area, particularly in the oak forest stand.

The effect of deep percolation in agricultural lands on contaminant concentration of groundwater

Balance management and the health improvement of the limited groundwater resources are unavoidable to prevent of water scarcity. The irrigation drainable water is the main factors of groundwater contamination that depended on leaching amount, type of surface contaminants and used fertilizer provided the different levels of pollution. In this research, the effect of deep percolation amount on nitrate concentration and salinity in Shahrekord plain is analyzed. The sensitivity of chemical parameters such as Ca, SO4, Cl, Na, K, HCO3 relative to season variation, also nitrate distribution in 80 to 86 years are investigated. For this subject, 10 agricultural areas were identified and estimated their discharge volume and deep percolation. The result show that the groundwater nitrate concentration in the summer season is depended on depletion volume from the effective limitation with R-squared value equal to 0.9, except two cases that NO3 is under the wastewater effect. Na, K and HCO3 in the winter season have a significant difference rather than summer. Also nitrate mapping indicated that the considerable part of groundwater nitrate is happen by leaching in the agricultural lands.

Modelling Projected Changes in Soil Water Budget in Coastal Kenya under Different Long-Term Climate Change Scenarios

The possible impacts that climate change will have on soil water budget and specifically on deep percolation, runoff and soil water content have been investigated using HYDRUS, a methodology based on numerical modelling simulations of vertical water movement in a homogenous soil column on a flat surface. This study was carried out on four typical soil types occurring on the Kenyan coast and the adjacent hinterlands of up to an elevation of 200 m above sea level (m a.s.l.) covered by five weather stations (two dry and three wet stations). Results show that deep percolation and runoff are expected to be higher in 2100 for both Relative Concentration Pathways (RCPs) 2.6 and 8.5 scenarios than they were for the reference period (1986–2005). The average deep percolation is expected to increase by 14% for RCP 2.6 and 10% for the RCP 8.5, while the average runoff is expected to increase by 188% and 284% for the same scenarios. Soil water content is expected to either increase marginally or reduce depend in the same scenarios. The average soil water content is also expected to increase by 1% in the RCP 2.6 scenario and to decrease by 2% in the RCP 8.5 scenario. Increase in deep percolation through clay soil is expected to be the largest (29% in both scenarios), while sandy and sandy clay soil are expected to be the least influenced with an average increase of only 2%. Climate change is expected to impact runoff mostly in sandy soils, whereas the least affected would be clay loam soils. These results further support the assertion that the change in climate is expected to impact the recharge of aquifers by triggering an increase in infiltration under both scenarios.

Modeling Travel Time Distributions of Preferential Subsurface Runoff, Deep Percolation and Transpiration at A Montane Forest Hillslope Site

Residence and travel times of water in headwater catchments, or their smaller spatial units, such as individual hillslopes, represent important descriptors of catchments’ hydrological regime. In this study, travel time distributions and residence times were evaluated for a montane forest hillslope site. A two-dimensional dual-continuum model, previously validated on water flow and oxygen-18 data, was used to simulate the seasonal soil water regime and selected major rainfall–runoff events observed at the hillslope site. The model was subsequently used to generate hillslope breakthrough curves of a fictitious conservative tracer applied at the hillslope surface in the form of the Dirac impulse. The simulated tracer breakthroughs allowed us to estimate the travel time distributions of soil water associated with the episodic subsurface stormflow, deep percolation and transpiration, thus yielding partial travel time distributions for the individual discharge processes. The travel time distributions determined for stormflow were dominated by the lateral component of preferential flow. The stormflow median travel times, calculated for nine selected rainfall–runoff events, varied considerably—ranging from 1 to 17 days. The estimated travel times were significantly affected by the temporal rainfall patterns and antecedent soil moisture distributions. The residence times of soil water, evaluated for three consecutive growing seasons, ranged from 29 to 37 days. The analysis reveals the interplay of soil water storage and discharge processes at the hillslope site of interest. The applied methodology can be used for the evaluation of runoff dynamics at the hillslope and catchment scales as well as for the quantification of biogeochemical transformations of dissolved chemicals.

Assessment of straight and meandering furrow irrigation strategies under different inflow rates

This paper reports the effect of straight furrow (SF) and meandering furrow (MF) irrigation strategies, as well as inflow rate, on infiltration and hydraulic parameters including advance time, recession time, and runoff hydrograph. The performance of SF and MF irrigation in terms of runoff ratio, deep percolation, and application efficiency was evaluated in 6 furrow fields at Shahid Bahonar University of Kerman, Iran. The required data were collected from the farm, consisting of free drainage furrows with length 70 m, top width 0.8 m, depth 0.25 m, and slope 0.2%. The advance and recession times were significantly longer in MF than SF irrigation. The infiltration was estimated by Lewis-Kostiakov equation. The infiltration coefficients were calculated: The values of k were higher and of a were lower in MF furrows than in SF furrows. The average runoff ratio and application efficiency for the SF irrigation events were 50.53% and 49.07%, respectively, while those of the MF irrigation events were 7.04% and 52.94%, respectively. Based on the results, the velocity of water advance in MF irrigation is decreased and, thus, the runoff, erosion losses, mass of fertilizer lost and surface water contamination were reduced. Using a lower inflow rate and appropriate irrigation time leads to better management outcomes in irrigation systems.