Hydrology, Volume 9, Issue 9 (September 2022) – 11 articles

The climate is changing and its impacts on agriculture are a major concern worldwide. The impact of precipitation will influence crop yield and water management. Estimation of such impacts using inputs from the General Circulation Models (GCMs) for future years will therefore assist managers and policymakers. It is therefore important to evaluate GCMs on a local scale for an impact study. As a result, under the Shared Socioeconomic Pathways (SSPs) future climate scenarios, namely SSP245, SSP370, and SSP585, simulations of mean monthly and daily precipitation across Brunei Darussalam in Phase 6 of the Coupled Model Intercomparison Project (CMIP6) were evaluated. The performance of two multi-model ensemble (MME) methods is compared in this study: the basic Arithmetic Mean (AM) of MME and the statistical downscaling (SD) of MME utilizing multiple linear regression (MLR). All precipitation simulations are bias-corrected using linear scaling (LS), and their performance is validated using statistical metrics such as Root Mean Square Error (RMSE) and coefficient of determination (R²). The adjusted mean monthly precipitation during the validation period (2010–2019) shows an improvement, especially for the SD model with R² = 0.85, 0.86 and 0.84 for SSP245, SSP370 and SSP585, respectively. Although the two models produced unsatisfying results in producing annual precipitation. Future analysis under the SD model shows that there will be a much lower average monthly trend in comparison with the observed trend. On the other hand, the forecasted monthly precipitation under AM predicted the same rainfall trend as the baseline period in the far future. It is projected that the annual precipitation in the near future will be reduced by at least 27% and 11% under the SD and AM models, respectively. In the long term, less annual precipitation changes for the SD model (17%). While the AM model estimated a decrease in precipitation by at least 14%. Full article

Stream channelization, which entails reducing the sinuosity of a stream, widening, and in some cases deepening the stream channel, is a widespread practice in agricultural regions. Channelization efforts in central Illinois have significant impacts on the geomorphology, flow regime, and sediment transport both in and adjacent to modified reaches. The goal of this study was to characterize the changes in stream channels by comparing three streams that are at various stages of recovery post channelization, 5 years (1900N), 7 years (Frog), and 35 years (Bray), to an unmodified stream reach (Crooked) and estimate a recovery rate. Measured channel slopes within the modified streams were one order of magnitude larger than the measured channelized streams in Crooked. The two streams most recently channelized exhibited little geomorphic change since their channelization, while the segment modified 35 years ago experienced bank failure and immature meander development. The lack of redevelopment resulted in sinuosity values lower than that of Crooked, and the reestablishment of meanders similar to Crooked would take an estimated 11,000 years. The distributions of the sediments within all the streams comprised poorly sorted sand and pebbles. The distribution of the sediment resembles the source, the glacial diamicton that serves as the surficial sediments. Mobilization of the sediment is frequent, with recorded scour greater than sedimentation. Overall, the channelized segments experienced limited recovery. The segments are still degrading (1900N and Frog) or are transitioning into a threshold stage (Bray). Full article

The Harvard Water Program is more than sixty years old. It was directed by an academic Steering Committee consisting of the professors of Government and Political Science, Planning, Economics, and Water Engineering. In 2022 we would add to the notional Steering Committee the professors of Ecology, Sociology and Water Law, calling it the augmented Harvard eutopian approach to the design and operation of Water Resource Systems. We use the Greek word ‘eu-topos’ to mean ‘a good place’, figuratively speaking, and ‘dys-topos’ its antonym, ‘not a good place’. By opposing eutopia and dystopia (latin forms) (Utopian literature begins with Thomas More’s (1478–1535) fictional socio-political satire “Utopia”, written in Latin and published in 1516: “Libellus vere aureus, nec minus salutaris quam festivus, de optimo rei publicae statu deque nova insula Utopia”. “A little, true book, not less beneficial than enjoyable, about how things should be in a state and about the new island Utopia” [Wikipedia translation]. He coined the word ‘utopia’ from the Greek ou-topos meaning ‘no place’ or ‘nowhere’. It was a pun-the almost identical Greek word eu-topos means ‘a good place’), we pass judgement on three Irish case studies, in whole and in part. The first case study deals with the dystopian measurement of the land phase of the hydrological cycle. The system components are distributed among many government departments that see little need to cooperate, leading to proposition 1: A call for a new Water Law. The second case study deals with a project to restore a 200 km² polder landscape to its condition in 1957. The project came to the University with an hypothetical cause of the increased flooding and a tentative solution: dredge the Cashen estuary of its sand, speeding the flow of sluiced water to the sea, and the status quo ante would be restored. The first scientific innovation was the proof that restoration by dredging is impossible. Pumping is the only solution, but it raises disruptive questions that are not covered by Statute. The second important innovation was the discovery in the dynamic water balance, of large leakage into the polders, either around or between sluiced culverts, when the flap valves are nominally closed, impacting both their maintenance and minimization of pumping. Discussions on our findings ended in dystopian silence. Hence proposition 2: Moving towards eutopia may only be possible with a change in the Law. The third case study concerns the protection of Cork City from flooding: riverine, tidal and groundwater. The government’s “emerging solution” consists of major physical intervention in the city centre, driven hard against local opposition, as the only possible solution. Two hydro-electric reservoirs upstream were largely ignored as part of a solution because the relevant Statute did not mandate their use for flood control. The Supreme Court has recently overturned this interpretation of the governing Statute. A new theory of flood control with a cascade of reservoirs, dams and weirs is the scientific innovation here. Once more these findings have been greeted by government with dystopian silence. Hence proposition 3: Re-open the design process to find several much better solutions, approximating a eutopian water world. Full article

Hydrologic modeling in Nigeria is plagued by non-existent or paucity of hydro-metrological/morphological records, which has detrimental impacts on sustainable water resource management and agricultural production. Nowadays, freely accessible remotely sensed products are used as inputs in hydrologic modeling, especially in regions with deficient observed records. Therefore, it is appropriate to utilize the fine-resolution spatial coverage offered by these products in a parameter regionalization method that supports sub-grid variability. This study assessed the transferability of optimized model parameters from a gauged to an ungauged basin using the mesoscale Hydrologic Model (mHM)—Multiscale Parameter Regionalization (MPR) technique. The ability of the fifth generation European Centre for Medium-Range Weather Forecasts Reanalysis product (ERA5), Climate Hazards Group InfraRed Precipitation with Station data (CHIRPS), Global Precipitation Climatology Centre (GPCC), and Multi-Source Weighted-Ensemble Precipitation (MSWEP) gridded rainfall products to simulate observed discharge in three basins was first assessed. Thereafter, the CHIRPS rainfall product was used in three multi-basin mHM setups. Optimized model parameters were then transferred to independent basins, and the reproduction of observed discharges was assessed. Kling–Gupta Efficiency (KGE) scores showed improvements when mHM runs were performed using optimized parameters in comparison to using default parameters for discharge simulations. Optimized mHM runs performed reasonably (KGE > 0.4) for all basins and rainfall products. However, only one basin showed a satisfactory KGE value (KGE = 0.54) when optimized parameters were transferred to an ungauged basin. This study underscores the utility of the mHM-MPR tool for parameter transferability during discharge simulation in data-scarce regions. Full article

Wildfire increases the magnitude of runoff in catchments, leading to the degradation of ecosystems, risk to infrastructure, and loss of life. The Labor Day Fires of 2020 provided an opportunity to compare multiple large and severe wildfires with the objective of determining potential changes to hydrologic processes in Oregon Cascades watersheds. Geographic information systems (GIS) were implemented to determine the total percentage burned and percentage of high burn severity class of six watersheds on the west slope of the Oregon Cascade Range. In addition, two control watersheds were included to contrast the influence of climatic effects. Spatial arrangements of burned patches were investigated for correlation to streamflow response by utilizing landscape metrics algorithms, including Largest Patch Index (LPI), mean gyration (GYRATE), Contiguity Index (CONTIG), Patch Cohesion Index (COHESION), and Clumpiness Index (CLUMPY). Results of the first-year post-fire response were consistent with other studies of fire effects in the Pacific Northwest (PNW) and indicated changes to runoff dynamics were difficult to detect with inferential statistics, but the largest changes in runoff coefficients occurred in watersheds having the greatest percentage burned. Correlation analysis indicated relationships between event runoff coefficients and percentage burned during the 2020 fire season. Control watersheds show confounding runoff coefficients, point to the influence of ongoing drought, and complicate conclusions about the role of spatial burn severity patterns. These results could guide future post-fire studies of spatial patterns of burn severity and could assist watershed managers to prioritize at-risk PNW catchments to minimize harm to ecological and societal values. Full article

The flux of water through the hyporheic zone (HZ) is controlled by stream bedforms, sinuosity, surface water velocity, local water table, seasonality, and hydraulic conductivity (K) of the bed material. Dependent on both the kinematic viscosity and density of water, K values are a function of temperature. In most studies, changes in temperature have been neglected because of the limited effect either density or viscosity has on K values. However, these variations are important given the role of K in HZ flux, which lead to the hypothesis that flow into the HZ would be more efficient (faster rate and greater depth) under warmer conditions than under cool conditions. To discern how water temperature affects flow depth in the HZ, VS2DHI simulations were created to map flow under both warm and cool thermal conditions. The models employed data collected from a series of varying temperature hydrologic flume tests in which the effects of hyporheic flow altering variables such as sinuosity, surface water velocity and volume, and bed-forms were controlled. Results verify that K values in the HZ were larger under warm conditions generating deeper HZ pathways, while the smaller K values under cool conditions produced shallower pathways. The simulations confirmed a faster speed of frontal movement under warm conditions than cool. Péclet numbers revealed a shallower advective extinction depth under cool conditions as opposed to warm. Full article

Snowpack loss in midlatitude mountains is ubiquitously projected by Earth system models, though the magnitudes, persistence, and time horizons of decline vary. Using daily downscaled hydroclimate and snow projections, we examine changes in snow seasonality across the U.S. Pacific Southwest region during a simulated severe 20-year dry spell in the 21st century (2051–2070) developed as part of the 4th California Climate Change Assessment to provide a “stress test” for water resources. Across California’s mountains, substantial declines (30–100% loss) in median peak annual snow water equivalent accompany changes in snow seasonality throughout the region compared to the historic period. We find that 80% of historic seasonal snowpacks transition to ephemeral conditions. Subsetting empirical-statistical wildfire projections for California by snow seasonality transition regions indicates a two-to-four-fold increase in the area burned, consistent with recent observations of high elevation wildfires following extended drought conditions. By analyzing six of the major California snow-fed river systems, we demonstrate snowpack reductions and seasonality transitions result in concomitant declines in annual runoff (47–58% of historical values). The negative impacts to statewide water supply reliability by the projected dry spell will likely be magnified by changes in snowpack seasonality and increased wildfire activity. Full article

One of the most important parts of the hydrological cycle is evapotranspiration (ET). Accurate estimates of ET in irrigated regions are critical to the planning, control, and regulation of agricultural natural resources. Accurate ET estimation is necessary for agricultural irrigation scheduling. ET is a nonlinear and complex process that cannot be calculated directly. Reference evapotranspiration (RET) and potential evapotranspiration (PET) are two primary forms of ET. The ideas, equations, and application areas for PET and RET are different. These two terms have been confused and used interchangeably by researchers. Therefore, terminology clarification is necessary to ensure their proper use. The research indicates that PET and RET concepts have a long and distinguished history. Thornthwaite devised the original PET idea, and it has been used ever since, although with several improvements. The development of RET, although initially confused with that of PET, was formally defined as a standard method. In this study, the Preferred Reporting Item for Systematic reviews and Meta-Analysis (PRISMA) was used. Equations for RET estimation were retrieved from 44 research articles, and equations for PET estimation were collected from 26 studies. Both the PET and RET equations were divided into three distinct categories: temperature-based, radiation-based, and combination-based. The results show that, among temperature-based equations for PET, Thornthwaite’s (1948) equation was mentioned in 12,117 publications, whereas among temperature-based equations for RET, Hargreaves and Samani’s (1985) equation was quoted in 3859 studies. Similarly, Priestley (1972) had the most highly cited equation in radiation-based PET equations (about 6379), whereas Ritchie (1972) had the most highly cited RET equations (around 2382) in radiation-based equations. Additionally, among combination-based PET equations, Penman and Monteith’s (1948) equations were cited in 9307 research studies, but the equations of Allen et al. (1998) were the subject of a significant number of citations from 23,000 publications. Based on application, PET is most often applied in the fields of hydrology, meteorology, and climatology, whereas RET is more frequently utilized in the fields of agronomy, agriculture, irrigation, and ecology. PET has been used to derive drought indices, whereas RET has been employed for single crop and dual crop coefficient approaches. This work examines and describes the ideas and methodologies, widely used equations, applications, and advanced approaches associated with PET and RET, and discusses future enhancements to increase the accuracy of ET calculation to attain accurate agricultural irrigation scheduling. The use of advanced tools such as remote sensing and satellite technologies, in addition to machine learning algorithms, will help to improve the accuracy of PET and RET estimates. Researchers will be able to distinguish between PET and RET in the future with the use of the study’s results. Full article

The Magnitude and occurrence of extreme low flow events are needed in setting minimum flows to protect the instream users. As the true distribution is not normally known, the identification of the most appropriate distribution function that describes the extreme low flow data of a catchment is essential in estimating reliable low flow quantiles at various average recurrence intervals (ARI). The aim of this study is to conduct a comparative assessment of the performance of three plausible distribution functions for estimating low flow quantiles. The investigation was carried out by using 27-gauge stations within South Australia (SA), the driest state in Australia. The best distribution function out of the three selected distributions; Log Normal (LN), Log Pearson Type 3 (LP3), and Generalized Extreme Value (GEV for each of the three selected annual minima series (7-day, 15-day and 30-day) at each gauged catchments was identified. The estimated low flow quantiles from using these three distribution functions were compared using RMSE values estimated through Monte Carlo simulation studies. For the majority of the selected study catchments, GEV fitted using L moments was found to be the best method for estimating low flow quantiles at ARIs over 10 years (≥14%), while at low ARI, LP3 fitted using the Method of Moments (MOM) was shown to outperform (≥17%) the other methods. Full article

In the current study, efforts were made to standardize fertigation for providing the recommended doses of fertilizers (RDF) i.e., 300, 260, and 200 g/plant/year for N, P, and K, respectively, together with optimization of irrigation scheduling so that guava plants could avoid the frequent episodes of nutritional stress, water scarcity, or overwatering. The experiment’s execution was confined to a three-factor randomized block design, with a total of 19 treatments that were replicated four times. Briefly, these treatments included drip irrigation and nutrient (NPK) application through fertigation dosages (RDF; 100, 80, and 60%) with and without silver-black plastic mulching. Different applied fertilizer dosages, together with different levels of irrigation and soil mulching, had a significant impact on the guava plant’s vegetative, reproductive, and nutritional aspects. Under silver-black plastic mulch, drip irrigation at cumulative pan evaporation (CPE) 80 and 100% of the prescribed dosage of fertilizers, better macronutrient availability in the soil, and improved plant development were recorded (M₁DI₂F₁). Overall, using drip fertigation to provide NPK fertilizers close to the root zone increased the availability of nutrients to the plants as compared to the traditional fertigation and irrigation methods. Thus, this sustainable high-tech horticultural approach could be analyzed for its efficacy or applied to other crops to obtain adequate economic outcomes. Full article