Effects of Dam Construction in the Wang River on Sediment Regimes in the Chao Phraya River Basin

The Wang River is one of the major tributaries of the Chao Phraya River (CPR) system in Thailand as the key riverine sediment source supplying the Chao Phraya Delta that has experienced severe shoreline retreat in the past six decades. Historical and observed river flow and sediment data measured during 1929–2019 were used to assess the variation in total sediment load along the Wang River and evaluate the effects of three major dam constructions on sediment supplied from the Wang River to the CPR. Results indicated that sediment loads increased toward downstream. Variation in long-term total sediment load (TSL) along the river suggested that construction of the Kiew Lom Dam in 1972 did not cause a reduction in sediment yield in the Wang River Basin because it impounded less than 20% of the average annual runoff, while the Mae Chang and Kiew Koh Ma Dams caused downstream sediment reduction. These three dams are located in the upper and middle river basins, and their effects on sediment load in the Wang River are ameliorated by additional sediment supplied from the lower basin. Results confirmed that construction of these three major dams in the Wang River did not greatly impact sediment supply from the Wang River to the CPR system. The dam site and sediment load variation along the river are the primary factors controlling the impact of the dam construction.

Impacts of climate change on runoff in the source area of the Yellow River

The primary approach to realizing long-term runoff prediction involves combining a hydrological model with general circulation model. Previous studies on the Source area of the Yellow River were all based on the Coupled Model Intercomparison Project Phase 5 (CMIP5) data sets with defects in physical mechanisms. In this paper, the Beijing Climate Center Climate System Model (BCC-CSM2-MR) of CMIP6, which proved to perform well in arid and semi-arid regions, will be used to drive the Soil & Water Assessment Tool (SWAT) model and evaluate its applicability in runoff simulation at Tang Nahai Hydrological Station from 2011 to 2019. The occurrence of the extreme value of runoff, its change trend, and the year of abrupt change of runoff in the four Shared Socio-economic Pathway (SSP) scenarios (SSP1-2.6, 2-4.5, 3-7.0, and 5-8.5) during 2021-2100 were analyzed. The results show that: (1) the runoff simulation evaluation index of SWAT driven by BCC-CSM2-MR in the research area from 2011 to 2019 is excellent, and the runoff simulation in the future is reliable and effective. (2) only the average annual runoff in scenario 5-8.5 (708.5m /s) from 2021 to 2100 was significantly higher than that in 2011-2019. Other scenarios are close to or less than the annual runoff observed. Most importantly, the maximum and minimum annual runoff values under the four scenarios all occurred during 2060-2080, so the attribution analysis of runoff extremum during 2060-2080 is worth further study. (3) it is necessary to evaluate whether the existing reservoirs and hydropower stations in the Yellow River basin can reasonably regulate and utilize the annual runoff under scenario 5-8.5.

Responses of Hydrological Processes under Different Shared Socioeconomic Pathway Scenarios in the Huaihe River Basin, China

The Coupled Model Intercomparison Project Phase 6 (CMIP6) provides more scenarios and reliable climate change results for improving the accuracy of future hydrological parameter change analysis. This study uses five CMIP6 global climate models (GCMs) to drive the variable infiltration capacity (VIC) model, and then simulates the hydrological response of the upper and middle Huaihe River Basin (UMHRB) under future shared socioeconomic pathway scenarios (SSPs). The results show that the five-GCM ensemble improves the simulation accuracy compared to a single model. The climate over the UMHRB likely becomes warmer. The general trend of future precipitation is projected to increase, and the increased rates are higher in spring and winter than in summer and autumn. Changes in annual evapotranspiration are basically consistent with precipitation, but seasonal evapotranspiration shows different changes (0–18%). The average annual runoff will increase in a wavelike manner, and the change patterns of runoff follow that of seasonal precipitation. Changes in soil moisture are not obvious, and the annual soil moisture increases slightly. In the intrayear process, soil moisture decreases slightly in autumn. The research results will enhance a more realistic understanding of the future hydrological response of the UMHRB and assist decision-makers in developing watershed flood risk-management measures and water and soil conservation plans.

Evaluating watershed hydrological responses to climate changes at Hangar Watershed, Ethiopia

The aim of this study is to model the responses of Hangar Watershed hydrology to future climate changes under two representative concentration pathway (RCP) scenarios. Future changes in precipitation and temperature were produced using the output of dynamically downscaled data of a regional climate model (RCM) 0.44° resolution under RCP 4.5 and 8.5 scenarios for 2025–2055 and 2056–2086. The future projection of the RCM model of precipitation and temperatures showed an increasing trend relative to the base period (1987–2017). At 2025–2055 average annual precipitation increments of +15.7 and +19.8% were expected for RCP 4.5 and RCP 8.5, respectively. For 2056–2086 of RCP 4.5 and 8.5, a similar trend was also shown as average annual precipitation may increase by +20.1 and +23.4%, respectively. The changes of climate parameters were used as input into the SWAT hydrological model to simulate the future runoff at Hangar Watershed. The increment in precipitation projection resulted in a positive magnitude impact on average runoff flow. The average annual change in runoff at 2025–2055 of both RCP 4.5 and 8.5 may increase by +24.5 and +23.6%, respectively. In 2056–2086, a change in average annual runoff of +73.2 and +73.2% for RCP 4.5 and 8.5 may be expected, respectively.

Finding strategies to reduce soil erosion using modelling tools: a case study in olive orchards of Cordoba (Spain) including sheet and rill erosion, ephemeral and permanent gullies

<p>Agricultural activity can have a significant effect on the environment. Often, the lack of experimental data leaves simulation models as the only alternative for understanding and assessing such effects and they can be useful for exploring the response of agricultural systems to different scenarios, in order, for example, to minimize soil erosion or the pollution of watercourses by agrochemicals.</p><p>In this work we present a simulation exercise of the runoff and erosion in two typical olive groves of the Cordoba countryside with contrasting characteristics during the 2009-19 period. The model used is AnnAGNPS, widely tested and very well suited for use in agricultural environments. The specific objectives are: to analyze the applicability of the model confronting its results with data from other nearby areas; to determine the controlling factors of runoff and erosion, such as seasonality; to quantify the importance of the main types of erosion; to explore the response to two different management scenarios.</p><p>The study areas were two, Matasanos (189.4 ha of intensive olive groves on vertisols) and Morente (4.2 ha of traditional olive groves on degraded and poor vertisols). The first scenario (TC) consists of maintaining the soil bare by means of continuous conventional tillage. The second (CC) considers a temporary vegetation cover (around 70 %) on the lanes. All the possible types of erosion in those areas are considered: sheet and rill, ephemeral gullies (EG) and permanent gullies (PG). For the purposes of the simulations, the EGs are tilled while the PGs are not. The latter show more constant characteristics over time (although they also evolve), and are larger in size (i.e., they were assigned a greater depth).</p><p>The results show a significant decrease in average annual runoff in CC with respect to TC (38% in Matasanos and 55% in Morente), which is concentrated in the late autumn and winter months. Thus, according to our simulations, still preliminary, the implementation of covers would have achieved one of its objectives, which is to reduce the runoff generated in the watersheds.</p><p>The sediment yields in both watershed outlets also suffered a significant decrease in CC with respect to TC, going from 4.75 to 1.66 Mg/ha/year and from 16.2 to 6.9 Mg/ha/year in Matasanos and Morente respectively. The simulated erosion rates are consistent with observations made in the area and with other previous simulation exercises. Both sediment export and runoff show a marked seasonality, although erosion occurs somewhat more distributed throughout the year. The different types of erosion take on different importance in each watershed. For example, permanent gullies play a very important role in Morente (46% in TC and 44% in CC), despite they are active at very specific times, probably with extreme events, which is reasonable according to the observations made in the area. The results show that the model is apparently useful with respect to the proposed objectives, allowing the effect of different uses and management on the environment to be contrasted in the medium and long term.</p>

An Attempt to Decompose the Impact of Land Use and Climate Change on Annual Runoff in a Small Agricultural Catchment

The aims of this study are: i) to better understand the coupled interactions between land use changes, climate change and the aquatic ecosystem in a small agricultural catchment (<100 km2) with a long observation history (1963–2018) and a known land use history, and ii) to test available approaches to separate land use and climate change impacts on water resources in such a small catchment. The pre- and post-change periods have been separated based on change points and the known land use history. Next, conceptual and analytical approaches were applied to quantify and to distinguish between the impacts of climate and land use changes on annual runoff for these two periods. Over the observation period, both land use changes (increase in forest areas) as well as climate change (a temperature rise and a decrease in annual precipitation) occurred. These changes contributed to a decrease in the average annual runoff by 51.9 mm (49% of the long-term average) during the observation period. The quantified contributions of climate and land use changes to the decrease in the mean annual runoff amount to between 60% and 80% and between 40% and 20%, respectively. (i) The results obtained from different methods were consistent - a change in runoff was primarily caused by shifts in climatic variables. (ii) However, the quantified contributions varied depending on the method applied and the form of the Budyko curve. (iii) Thus, special care should be taken in relation to the selection of the Budyko curve for quantifying these changes. (iv) Knowledge of the water deficit sources can result in better planning of water resources management in such small catchments.

Changes in Runoff and Sediment Load and Potential Causes in the Malian River Basin on the Loess Plateau

The loessial tableland is a unique landform type on the Loess Plateau in China. Long-term soil erosion has led to the retreat of gullies and the rapid reduction of fertile arable land, which has further decreased agricultural production. In this study, we chose the Malian River basin to analyze the temporal and spatial variation of its runoff and sediment load, as well as the potential causes. The annual runoff and sediment load at six hydrological stations in the study area were collected for the period between 1960 and 2016. The Mann−Kendall and Pettitt tests were respectively applied to detect temporal variations and abrupt changes in the runoff and sediment loads. The results showed that an abrupt change in the runoff and sediment loads occurred in 2003. The average annual runoff in the Malian River was 4.42 × 108 m3 yr−1 from 1960 to 2002, and decreased to 3.32 × 108 m3 yr−1 in 2003–2016. The average annual sediment load was 1.27 × 108 t yr−1 in 1960–2002, and decreased to 0.65 × 108 t yr−1 in 2003–2016. The spatial patterns in the sediment load suggested that the Hongde sub-basin contributed a higher sediment count to the Malian River, which may require additional attention for soil and water conservation in the future. Anthropogenic activities significantly affected runoff and sediment load reduction according to the double-mass curve method, accounting for 90.7% and 78.7%, respectively, whereas rainfall changes were 9.3% and 21.3%, respectively. As such, the present study analyzed the loessial tableland runoff and sediment load characteristics of the Malian River basin for soil and water erosion management.

River Lan discharge: current state and forecast

The results of the study of the water regime of the Lan River, a typical small river of the Belarusian Polesye, are presented. The Lan River is represented by three monitoring sites (Lognovichi, Loktyshi and Mokrovo) with drainage areas A = 480 km2, A = 909 km2 and A = 2550 km2, respectively, with different observation periods and the degree of anthropogenic impact. In addition to large-scale reclamation in the river basin, carried out in the middle of the last century, in 1977, a reservoir was built in the river bed for fish farming and agricultural use. Using the method of analogies, the series of observations of annual, maximum, minimum summer-autumn and winter water discharges are reduced to a single calculated period of 68 years from 1948 to 2015. Assessment of the influence of anthropogenic impacts and natural factors on the runoff, the initial time series, the averaging intervals were analyzed: from 1948 to 2015. (the entire observation period length is 68 years); from 1948 to 1977 (29 years period before the commissioning of the Loktyshi reservoir); from 1978 to 2015 (38 years of reservoir operation period); from 1978 to 1987 (10 years period of the reservoir functioning before the beginning of the modern climate warming,); from 1988 to 2015 (27 years period of the reservoir functioning under the current climate warming). Statistical heterogeneity was found as a result of intensive economic activity, which significantly disrupts the natural hydrological regime. It was revealed that for the average annual runoff there is a decrease along the Lognovichi site and an increase along the Loktyshi site; for the maximum runoff, a decrease is observed along all the stations under consideration; for the minimum summer-autumn discharge, an increase is observed along the Loktyshi site; for the minimum winter runoff, an increase is observed along all stations. Based on the hydrological and climatic hypothesis, predictive estimates of the average discharge values for the period of 2050 are given, which are expressed in a certain decrease in it and a shift in the peak of spring flood to earlier dates.

Assessment of Surface Runoff using ArcSWAT for Rela Watershed, Rajasthan, India

The current study based on SWAT (Soil and Water Assessment Tool) Model which coordinates the GIS data with attribute database set to assess the runoff of Rela Watershed. Soil and Water Assessment Tool (SWAT) is based on distributed parameter model which has been created to forecast runoff, sediment, erosion and nutrient transport from agrarian watersheds under various management practices. The SWAT Model works related to Arc GIS. In the current study the catchment region has been delineated utilizing the DEM (Digital Elevation Model) and afterward partitioned into 29 sub-watersheds or sub-basins. For planning of landuse map, the LANDSAT images are downloaded from earth explorer and the soil mapis obtained from NBSS (National Bureau of Soil Survey, Udaipur). The sub basins are partitioned into 29 HRUs which represents Hydrological Response Unit. At that point by utilizing 30 years of every day precipitation information and daily minimum and maximum temperature information SWAT simulation is accomplished for consistent schedule to estimate Runoff. The insights indicated diverse runoff framework esteem during the time 19.5 mm being the most minimal and 527.3 mm being the maximum runoff for Rela Watershed. The average annual runoff is 162.6 mm i.e. 28% of total rainfall in Rela Watershed.

Runoff sensitivity to climate and land-use changes: A case study in the Longtan basin, Southwestern China

Based on the scenario hypothesis method, this paper applied a Soil and Water Assessment Tool (SWAT) to analyze the sensitivity of runoff to climate and land-use changes in the Longtan basin, China. Results indicated that (1) for every 1 °C increase in temperature, the average annual runoff decreased by 9.9 mm, and the average annual evaporation increased by 9.3 mm. However, for every 10% increase in rainfall, the average annual runoff and evapotranspiration increased by 96.3 mm and 11.53 mm, respectively. Obviously, runoff was more sensitive to the change in rainfall than temperature in the Longtan basin. Meanwhile, (2) forestland could conserve water resources, but its water consumption was larger. Although grassland played a relatively small role in water conservation, it consumed less water. At the same time, increasing the area of forestland and grassland could weaken peak floods, and the water retention function of vegetation could prevent runoff from increasing and decreasing steeply. Therefore, it is worth improving vegetation coverage.