Hydrology, Volume 4, Issue 4 (December 2017) – 17 articles

The Gulf of Alaska is a highly productive ecosystem that supports fisheries and subsistence harvesting of marine resources. The highly productive summer season begins with a bloom that is dominated by diatoms. Both river and submarine groundwater discharge have been recognized as substantial terrestrial nutrient (nitrate and silicate) sources to the Gulf’s coastal waters. Here, the response of in-situ phytoplankton to groundwater and river water additions was evaluated via a bioassay incubation experiment. Special attention was given to diatom genera, as previous studies have shown that submarine groundwater discharge preferentially induces growth of diatoms. The abundance of Pseudo-nitzschia spp., Chaetoceros spp., and Leptocylindrus spp. increased significantly in groundwater and river water containing treatments. Although groundwater and river water are both rich in nitrate and silicate, groundwater treatments with a higher salinity favored a higher relative abundance of Pseudo-nitzschia spp. Conversely, in the highest river water concentration treatments with lower salinity, relative abundances of Pseudo-nitzschia spp. decreased, while Chaetoceros spp. and Leptocylindrus spp. increased. Total abundances of all three genera increased in the lower salinity treatments. These findings could portend changes in the phytoplankton community composition in the Gulf of Alaska as the climate warms and river discharge increases in the coming decades. Furthermore, the findings support previous assertions that submarine groundwater discharge, with higher salinity than river water, is a preferable source of nutrients to the genus Pseudo-nitzschia. Full article

Groundwater recharge remains almost totally unknown across the Mekong River Basin, hindering the evaluation of groundwater potential for irrigation. A regional regression model was developed to map groundwater recharge across the Lower Mekong Basin where agricultural water demand is increasing, especially during the dry season. The model was calibrated with baseflow computed with the local-minimum flow separation method applied to streamflow recorded in 65 unregulated sub-catchments since 1951. Our results, in agreement with previous local studies, indicate that spatial variations in groundwater recharge are predominantly controlled by the climate (rainfall and evapotranspiration) while aquifer characteristics seem to play a secondary role at this regional scale. While this analysis suggests large scope for expanding agricultural groundwater use, the map derived from this study provides a simple way to assess the limits of groundwater-fed irrigation development. Further data measurements to capture local variations in hydrogeology will be required to refine the evaluation of recharge rates to support practical implementations. Full article

The prediction of dominant hydrological processes is imperative with the available information in data scarce regions by means of the lumped hydrological models for the purpose of water resource management. This study is aims at an intercomparison of the performances of the conceptual hydrological models in predicting streamflow. The Veralgemeend Conceptueel Hydrologisch (VHM) and NedborAfstromnings Model (NAM) lumped rainfall–runoff models were manually calibrated and validated for periods of 1 January 1990–31 December 2000 and 1 January 2001–31 December 2005, respectively. Some of the parameters of the models (i.e., recession constants of subflow components) were estimated from the preprocessing of the streamflow data using the Water Engineering Time Series PROcessing tool (WETSPRO). These parameters were used for the initial model setup and subjected to slight adjustments during calibration. The performances of the models were evaluated by graphical and statistical means. The results depicted that the models reproduced the streamflow in a good way and that the overall shape of the hydrograph was properly captured. A Nash Sutcliffe efficiency (NSE) of 0.71 and 0.67 were obtained during calibration, whereas, for the validation period, NSE of 0.6 and 0.58 were obtained for VHM and NAM, respectively. The water balance discrepancy (WBD) of −0.1% and −13.7% were achieved for calibration, while −17% and −9% were acquired during validation for VHM and NAM, respectively. Though the models underestimated the high flows, the low flows were relatively well simulated. From the overall evaluation of the models, it is noted that the NAM model performed better than the VHM model in predicting the flow. In conclusion, the models can be used for water resource management and planning with precautions for extreme flow. Full article

The Pettitt abrupt change test method based on ArcGIS was used to undertake change-point analysis on climatic (precipitation and potential evapotranspiration; 39 meteorological stations) and runoff data (27 hydrological stations) from 1954–2015 in the Nenjiang basin. The hydrological sensitivity analysis method was also used to calculate the influential component of climate change upstream, mid-stream, and downstream of the Nenjiang basin, as well as the effect of anthropogenic activities on runoff. Our results show that the upstream area has the highest contribution rate of climate change, followed by the mid-stream area; the downstream area has the lowest contribution rate. Studying climate change contribution rates in various sites in the Nenjiang basin, in addition to anthropogenic activities affecting runoff, can provide the foundation for the protection and utilization of basin water resources, as well as the conservation and restoration of wetlands. Full article

Analysis and interpretation of soil properties dynamics is a keystone in understanding the hydrologic responses and yield potential of floodplain wetlands. This study characterizes the distribution and spatial trends of selected soil physical properties in the Kilombero floodplain, Tanzania. A total of 76 composite soil samples were taken from 0 to 20 cm and 20 to 40 cm depth in a regular grid design across three hydrological zones, related to flooding intensity defined as fringe, middle, and riparian during the rainy season of 2015. The samples were analyzed for soil texture, bulk density, organic carbon, and saturated hydraulic conductivity. Seasonal soil moisture content was monitored at depths of 10, 20, 30, and 40 cm, using 17 frequency domain reflectometry profile probes type PR2, installed at each hydrological zone for 18 months (March 2015–August 2016). Data were subjected to classical statistical and geostatistical analyses. Results showed significant (p < 0.05) differences in bulk density, texture, soil organic carbon (SOC), and saturated hydraulic conductivity (K_sat) across the hydrological zones. Bulk density showed a clear increasing trend towards the fringe zone. Mean K_sat was highest at the riparian zone (69.15 cm·d⁻¹), and clay was higher in the riparian (20.3%) and middle (28.7%) zones, whereas fringe had the highest percentage of sand (33.7–35.9%). Geostatistical spatial results indicated that bulk density, silt, and SOC at 0–20 cm had intermediate dependence, whereas other soil properties at both depths had high spatial dependence. Soil moisture content showed a significant (p < 0.05) difference across the hydrological zones. The riparian zone retained the highest soil moisture content compared to the middle and fringe zone. The temporal soil moisture pattern corresponded to rainfall seasonality and at the riparian zone, soil moisture exhibited a convex shape of sloping curve, whereas a concave sloping curve for topsoil and for the middle zone at the subsoil was observed during the start of the dry season. Our results are seen to contribute to a better understanding of the spatial distribution of soil properties and as a reference for soil and water management planning in the floodplain. Full article

This study is focused on establishing the extent of potential hydraulic connections of local lowland aquifers with the run-off waters of a nearby creek and two major rivers in and around Fort Riley in northeastern Kansas, USA. It is based on collective evidence by combining the contents of several major and trace elements of the waters with their oxygen, hydrogen and Sr isotopic compositions. The area of investigation is located a few miles to the west of the Kansas Konza Prairie, which is a United States designated site for regular monitoring of ecological and environmental configurations. The δ¹⁸O and δD of the run-off waters from the two rivers and the creek, and of the ground waters from local aquifers are almost identical. Relative to the General Meteoric Water Line, the δ¹⁸O-δD data have a tendency to deviate towards relatively lower δ¹⁸O values, as do generally the sub-surface waters of intra-continental basins. The observed stable isotope compositions for these waters preclude any significant impact by either an evapo-transpiration process by the vegetation, or an interaction with immediate mineral-rock matrices. The ⁸⁷Sr/⁸⁶Sr ratios of the aquifer waters collected from wells close to the Kansas River were markedly different from those of the river waters, confirming a lack of hydraulic interactions between the aquifers and the river. On the contrary, ground waters from wells at a relative distance from the Kansas River have ⁸⁷Sr/⁸⁶Sr ratios, Sr contents and Sr/Ca ratios that are similar to those of the river water, suggesting a hydraulic connection between these aquifers and the river, as well as a lack of any impact of the vegetation. An underground water supply from nearby Summer Hill located to the north of the study area has also been detected, except for its western border where no interactions occurred apparently between the aquifer waters and the reservoir rocks, or with the creek and river waters. The ⁸⁷Sr/⁸⁶Sr signatures of the ground waters suggest also a major east-west flow system in the study area that can be divided into three entities, together with a supplementary north-south trend along the Threemile creek towards the Kansas River. Full article

Climatic variations caused by the excessive emission of greenhouse gases are likely to change the patterns of precipitation, runoff processes, and water storage of river basins. Various studies have been conducted based on precipitation outputs of the global scale climatic models under different emission scenarios. However, there is a limitation in regional- and local-scale hydrological analysis on extreme floods with the combined application of high-resolution atmospheric general circulation models’ (AGCM) outputs and physically-based hydrological models (PBHM). This study has taken an effort to overcome that limitation in hydrological analysis. The present and future precipitation, river runoff, and inundation distributions for the Lower Mekong Basin (LMB) were analyzed to understand hydrological changes in the LMB under the RCP8.5 scenario. The downstream area beyond the Kratie gauging station, located in the Cambodia and Vietnam flood plains was considered as the LMB in this study. The bias-corrected precipitation outputs of the Japan Meteorological Research Institute atmospheric general circulation model (MRI-AGCM3.2S) with 20 km horizontal resolution were utilized as the precipitation inputs for basin-scale hydrological simulations. The present climate (1979–2003) was represented by the AMIP-type simulations while the future (2075–2099) climatic conditions were obtained based on the RCP8.5 greenhouse gas scenario. The entire hydrological system of the Mekong basin was modelled by the block-wise TOPMODEL (BTOP) hydrological model with 20 km resolution, while the LMB area was modelled by the rainfall-runoff-inundation (RRI) model with 2 km resolution, specifically to analyze floods under the aforementioned climatic conditions. The comparison of present and future river runoffs, inundation distributions and inundation volume changes were the outcomes of the study, which can be supportive information for the LMB flood management, water policy, and water resources development. Full article

An affordable standalone sensor that can provide volumetric information on soil moisture distribution in real time was developed and tested for potential application in irrigation control systems. The moisture content of soil is reconstructed tomographically from electrical resistivity measured between multiple pairs of electrodes, which are installed on two opposite sides of the soil volume. The measurement of relative moisture content reconstructed from the measured resistance values demonstrated in this paper requires a simple, in-situ, two-point calibration (for dry and wet soil conditions) after electrodes are installed in place. This calibration has to be repeated once the soil conditions, such as salinity or fertilizer content, are altered as the season progresses. Historical data collected over a 12-month period can be stored locally or transferred over a wireless network at given intervals or in real time. Although existing single-point sensors can provide more accurate measurements of soil moisture, knowledge on the three-dimensional distribution of moisture around plant roots should allow substantial savings of precious fresh water resources and more intelligent multi-channel irrigation systems. The same system can possibly be extended to estimation of fertilizer distribution. Full article

Accurate spatial and temporal representation of precipitation is of utmost importance for hydrological applications. Uncertainties in available data sets increase with spatial resolution due to small-scale processes over complex terrain. As previous studies revealed high regional differences in the performance of gridded precipitation data sets, it is important to assess the related uncertainties at the catchment scale, where these data sets are typically applied, e.g., for hydrological modeling. In this study, the uncertainty of eight gridded precipitation data sets from various sources is investigated over an alpine catchment. A high resolution reference data set is constructed from station data and applied to quantify the contribution of spatial resolution to the overall uncertainty. While the results demonstrate that the data sets reasonably capture inter-annual variability, they show large seasonal differences. These increase for daily indicators assessing dry and wet spells as well as heavy precipitation. Although the higher resolution data sets, independent of their source, show a better agreement, the coarser data sets showed great potential especially in the representation of the overall climatology. To bridge the gaps in data scarce areas and to overcome the issues with observational data sets (e.g., undercatch and station density) it is important to include a variety of data sets and select an ensemble for a robust representation of catchment precipitation. However, the study highlights the importance of a thorough assessment and a careful selection of the data sets, which should be tailored to the desired application. Full article

Sub-Saharan Africa is highly vulnerable to climate change given its low capacities of resilience to the enormous challenges climate change will pose. Research aimed at evaluating changes in hydrological trends and methods of adaptation was conducted in the Niger Basin parts of Benin at the peak of the rainy season in the year 2012. Rainfall and river discharge were analyzed from 1950–2010 in order to generate patterns of changes in the region. Structured questionnaires were used to evaluate the perceptions of 14 farming communities on climate-related issues and their methods of adaptations. Mann-Kendall and Pettit trend analyses were conducted for rainfall and river discharge. The findings indicated that significant decreases characterized rainfall and river discharge in the period of study. Flash flood was considered the major challenge faced in the region according to more than 90% of crop, animal, and fish farmers. Aside from that, decrease in water availability was identified as an additional challenge. Irrigation, diversification, water treatment, drainage, small dams, and dikes were reported as the common adaptation mechanisms in the catchments. This study will help in designing sustainable adaptation mechanisms to abrupt changes in the hydrology of the region. Full article

This work aims to evaluate future water availability in the Mékrou catchment under climate change scenarios. To reach this goal, data from Regional Climate Models (RCMs) were used as the input for four rainfall-runoff models which are ModHyPMA (Hydrological Model based on Least Action Principe), HBV (Hydrologiska Byråns Vattenbalansavdelning), AWBM (Australian Water Balance Model), and SimHyd (Simplified Hydrolog). Then the mean values of the hydro-meteorological data of three different projected periods (2011–2040, 2041–2070 and 2071–2100) were compared to their values in the baseline period. The results of calibration and validation of these models show that the meteorological data from RCMs give performances that are as good as performances obtained with the observed meteorological data in the baseline period. The comparison of the mean values of the hydro-meteorological data of the baseline period to their values for the different projected periods indicates that for PET there is a significantly increase until 2100 for both Representative Concentration Pathway 4.5 (RCP4.5) and RCP8.5 scenarios. Therefore, the rate’s increase of potential evapotranspiration (PET) under the RCP8.5 scenario is higher than that obtained under the RCP8.5 scenario. Changes in rainfall amounts depend on the scenario of climate change and the projected periods. For the RCP4.5 scenario, there is a little increase in the annual rainfall amounts over the period from 2011 to 2040, while there is a decrease in the rainfall amounts over the other two projected periods. According to the RCP8.5 scenario, the contrary of changes observed with the RCP4.5 scenario are observed. At a monthly scale, the rainfall amounts will increase for August and September and decrease for July and October. These changes in rainfall amounts greatly affect yearly and monthly discharge at the catchment outlet. Over the three projected periods and for both RCP4.5 and RCP8.5, the mean annual discharge will significantly increase related to the baseline periods. However, the magnitude of increases will depend on the projected period and the RCP scenario. At a monthly scale, it was found that runoff increases significantly from August to November for all projected periods and the climate change scenario. Full article

Finite element discretization of the pressure head form of the Richards equation leads to a nonlinear model, which yields numerical convergence difficulties. When the numerical solution to this problem has either an extremely sharp moving front, infiltration into dry soil, flow domains containing materials with spatially varying properties, or involves time-dependent boundary conditions, the corrector iteration used in many time integrators can terminate prematurely, which leads to incorrect results. While the Picard and Newton iteration methods can solve this problem through tightening the tolerances provided to the solvers, there is a more efficient approach to overcome the convergence difficulties. Four tests examples are examined, and each test case is solved with five sufficiently small tolerances to demonstrate the effectiveness of convergence. The numerical results illustrate that the methods greatly improve the convergence and stability. Test experiments show that the Newton method is more complex and expensive on a per iteration basis than the Picard method for simulating variably saturated–unsaturated flow in one spatial dimension. Consequently, it is suggested that the resulting local and global mass balance is exact within the minimum specified accuracy. Full article

Agricultural subsurface drainage changes the field hydrology and potentially the amount of water available to the crop by altering the flow path and the rate and timing of water removal. Evapotranspiration (ET) is normally among the largest components of the field water budget, and the changes in ET from the introduction of subsurface drainage are likely to have a greater influence on the overall water yield (surface runoff plus subsurface drainage) from subsurface drained (TD) fields compared to fields without subsurface drainage (UD). To test this hypothesis, we examined the impact of subsurface drainage on ET at two sites located in the Upper Midwest (North Dakota-Site 1 and South Dakota-Site 2) using the Landsat imagery-based METRIC (Mapping Evapotranspiration at high Resolution with Internalized Calibration) model. Site 1 was planted with corn (Zea mays L.) and soybean (Glycine max L.) during the 2009 and 2010 growing seasons, respectively. Site 2 was planted with corn for the 2013 growing season. During the corn growing seasons (2009 and 2013), differences between the total ET from TD and UD fields were less than 5 mm. For the soybean year (2010), ET from the UD field was 10% (53 mm) greater than that from the TD field. During the peak ET period from June to September for all study years, ET differences from TD and UD fields were within 15 mm (<3%). Overall, differences between daily ET from TD and UD fields were not statistically significant (p > 0.05) and showed no consistent relationship. Full article

Some of the problems in drought assessments are that: analyses tend to focus on coarse temporal scales, many of the methods yield skewed indices, a few terminologies are ambiguously used, and analyses comprise an implicit assumption that the observations come from a stationary process. To solve these problems, this paper introduces non-stationary frequency analyses of quantiles. How to use non-parametric rescaling to obtain robust indices that are not (or minimally) skewed is also introduced. To avoid ambiguity, some concepts on, e.g., incidence, extremity, etc., were revisited through shift from monthly to daily time scale. Demonstrations on the introduced methods were made using daily flow and precipitation insufficiency (precipitation minus potential evapotranspiration) from the Blue Nile basin in Africa. Results show that, when a significant trend exists in extreme events, stationarity-based quantiles can be far different from those when non-stationarity is considered. The introduced non-parametric indices were found to closely agree with the well-known standardized precipitation evapotranspiration indices in many aspects but skewness. Apart from revisiting some concepts, the advantages of the use of fine instead of coarse time scales in drought assessment were given. The links for obtaining freely downloadable tools on how to implement the introduced methods were provided. Full article

Understanding the impacts of climate change on water resources is of utmost importance to successful water management and further adaptations strategies. The objective of this paper is to assess the impacts of climate change on river discharge dynamics in Oueme River basin in Benin. To this end, this paper used the distribution based scaling approach to improve usability of regional climate model projections for hydrological climate change impacts studies. Hydrological simulations in Bétérou and Bonou sub-catchments of the Oueme River were carried out with a lumped conceptual hydrological model. The main contribution of this paper is to use the hydrological model based on the least action principle (HyMoLAP), which is designed to minimize uncertainties related to the rainfall-runoff process and scaling law, for this assessment. The bias correction approach allows reducing the differences between the observed rainfall and the regional climate model (HIRHAM5 and RCA4) rainfall data. Corrected and raw HIRHAM5 and RCA4 rainfall data were compared with the observed rainfall using Mean Absolute Error (MAE) and Root Mean Square error (RMSE). The results of the bias correction show a decrease in the RMSE and MAE of the raw HIRHAM5 and RCA4 rainfall data of approximately 91% to 98% in both catchments. The results of the simulation indicate that the HyMoLAP is suitable for modelling river discharge in the Oueme River basin. For the future projection based on RCP4.5 scenarios, the projected mean annual river discharge by using HIRHAM5 and RCA4 in Bétérou and Bonou decrease with the magnitude ranging respectively from −25% to −39% and −20% to −37% in the three time horizons 2020s (2011–2040), 2050s (2041–2070) and 2080s (2071–2100), representing the early, middle and late of 21st century. As regards the future projection based on RCP8.5 scenarios, the projected mean annual river discharge by using HIRHAM5 and RCA4 in Bétérou and Bonou decrease with the magnitude ranging respectively from −15% to −34% and −18% to −36% in the three time horizons. The model uncertainties projections indicated that the entire discharge distribution shifted toward more extreme events (such as drought) compared to the baseline period. Full article

A continuous spatio-temporal database of accurate soil moisture (SM) measurements is an important asset for agricultural activities, hydrologic studies, and environmental monitoring. The Advanced Microwave Scanning Radiometer 2 (AMSR2), which was launched in May 2012, has been providing SM data globally with a revisit period of two days. It is imperative to assess the quality of this data before performing any application. Since resources of accurate SM measurements are very limited in Puerto Rico, this research will assess the quality of the AMSR2 data by comparing it with ground-based measurements, as well as perform a downscaling technique to provide a better description of how the sensor perceives the surface soil moisture as it passes over the island. The comparison consisted of the evaluation of the mean error, root mean squared error, and the correlation coefficient. Two downscaling techniques were used, and their performances were studied. The results revealed that AMSR2 products tend to underestimate soil moisture. This is due to the extreme heterogeneous distributions of elevations, vegetation densities, soil types, and weather events on the island. This research provides a comprehensive study on the accuracy and potential of the AMSR2 products over Puerto Rico. Further studies are recommended to improve the AMSR2 products. Full article

Soil moisture is placed at the interface between land and atmosphere which influences water and energy flux. However, soil moisture information has a significant importance in hydrological modelling and environmental processes. Recent advances in acquiring soil moisture from the satellite and its effective utilization provide an alternative to the conventional soil moisture methods. In this study, an attempt is made to apply physically based, distributed-parameter, Soil and Water Assessment Tool (SWAT) to validate Advanced Microwave Scanning Radiometer (AMSR2) soil moisture in parts of Puerto Rico. For this, calibration is performed for the years 2010 to 2012 with known observed discharge sites, Rio Gunajibo and Rio Grande de Anasco in Puerto Rico and validation, with the observed stream flow for the year 2013 using the AMSR2 soil moisture. Moreover, the SWAT and AMSR2 soil moisture outcome are compared on a monthly basis. The model capability and performance in simulating the stream flow are evaluated utilizing the statistical method. The results indicated a negligible difference in SWAT soil moisture and AMSR2 soil moisture for stream flow estimation. Finally, the model retrievals show a satisfactory agreement between observed and simulated streamflow. Full article