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Analyzing the future changes in runoff is crucial for efficient water resources management and planning in arid regions with large river systems. This paper investigates the future runoffs of the headwaters of the Tarim River Basin under different emission scenarios by forcing the hydrological model SWAT-Glacier using six regional climate models from the Coordinated Regional Downscaling Experiment (CORDEX) project. Results indicate that compared to the period of 1976~2005, temperatures are projected to increase by 1.22 ± 0.72 °C during 2036~2065 under RCP8.5 scenarios, with a larger increment in the south Tianshan mountains and a lower increment in the north Kunlun Mountains. Precipitation is expected to increase by 3.81 ± 14.72 mm and 20.53 ± 27.65 mm during 2036–2065 and 2066–2095, respectively, under the RCP8.5 scenario. The mountainous runoffs of the four headwaters that directly recharge the mainstream of the Tarim River demonstrate an overall increasing trend in the 21st century. Under the RCP4.5 and RCP8.5 scenarios, the runoff is projected to increase by 3.2% and 3.9% (amounting to 7.84 × 108 m3 and 9.56 × 108 m3) in 2006–2035. Among them, the runoff of the Kaidu River, which is dominated by rainfall and snowmelt, is projected to present slightly decreasing trends of 3~8% under RCP4.5 and RCP8.5 scenarios. For catchments located in the north Kunlun Mountains (e.g., the Yarkant and Hotan Rivers which are mix-recharged by glacier melt, snowmelt, and rainfall), the runoff will increase significantly, especially in summer due to increased glacier melt and precipitation. Seasonally, the Kaidu River shows a forward shift in peak flow. The summer streamflow in the Yarkant and Hotan rivers is expected to increase significantly, which poses challenges in flood risk management. [ABSTRACT FROM AUTHOR]

The impact of climate change on surface runoff and soil moisture in the source region of the Yellow River is analyzed, which will provide a scientific basis for the rational use and protection of water resources in the source area. In this paper, the SWAT hydrological model was coupled with the Coupled Model Intercomparison Project (CMIP) to predict future changes in surface runoff and soil moisture in the source region of the Yellow River. The prediction of surface runoff and soil moisture in the Yellow River Basin was analyzed by a linear regression model. The SWAT model rate had a calibration period R2 of 0.876 and a validation period R2 of 0.972. The trend of surface runoff and annual mean temperature in the source region of the Yellow River from 2011 to 2022 showed an overall increasing trend, and soil moisture showed a general decreasing trend. 2011–2022 trends between surface runoff and annual mean temperature in the source region of the Yellow River showed a highly significant difference, indicating that surface runoff flow was significantly influenced by temperature. The difference between the trends in soil moisture and the annual mean temperature was highly significant. The surface runoff fluctuated greatly in different years, and the surface runoff changed greatly in different scenarios of CMIP5 (RCP2.6, RCP4.5, and RCP8.5). For all three climate change scenarios, the surface runoff displayed a downward trend. The surface runoff showed a similar uneven distribution for all scenarios on a yearly cycle. Under the three climate scenarios, the runoff was highest between May and August, with a slowly increasing trend from January to April and a slightly decreasing trend from September to December. The interannual and interannual distribution of soil water was basically consistent with the distribution of surface runoff, and there was an overall trend in the length of all soil water reduction scenarios. Surface runoff and soil moisture are and will be greatly affected by climate change (mainly temperature and precipitation). Under the three climate scenarios, the precipitation increases to some extent, but the surface runoff and soil moisture will both decrease, which may be attributed to the greater evaporation than the precipitation. [ABSTRACT FROM AUTHOR]

The paper presents a physically based mathematical model of the key hydrophysical processes of runoff formation at a catchment point over a long-term period. The model describes the freezing and thawing of soil, the formation and melting of the snow cover, the migration of moisture to the freezing front and the infiltration of rain and melt moisture, evaporation from snow, soil cover, vegetation, and water surface. Average daily values of meteorological parameters are used as initial information for mathematical modeling. The relevance of the study is caused by a need to reveal the main links between the processes of vertical heat and moisture exchange in soil and the environmental factors that determine their climate-driven nature. Using observational data from water balance stations, numerical experiments and an analysis of the influence of long-term variability of the key meteorological factors on evaporation from the land and water surface and on vertical moisture flows in soil were carried out. [ABSTRACT FROM AUTHOR]

The article considers an approach to evaluating the change in surface, subsurface and groundwater flow on a large river catchment exemplified by the Oka River basin. The study is based on the synthesis of a physical-mathematical model of runoff formation and atmosphere–ocean general circulation models. The paper presents the results of calibration and verification of a hydrological model over a period of history, as well as the assessment of reproduction accuracy of meteorological and hydrological characteristics according to the data of global climate models and observation data. Based on an ensemble of atmosphere–ocean general circulation models, the changes in meteorological (air temperature, precipitation, air humidity deficit) and hydrological (surface runoff, soil moisture content, groundwater flow) characteristics by the middle and the end of the 21st century have been calculated, under the scenarios RCP 2.6 and RCP 6.0 with regard to the historical period. [ABSTRACT FROM AUTHOR]

The natural water cycle in an urban catchment normally results from climate, physical characteristics and natural surface coverage. The hydrological process in urban catchments can drastically change due to urbanization, human activities, modified physiography and climate change. Urbanization typically results in a larger runoff volume, higher peak discharge, faster time of concentration as well as lower infiltration. It also has a significant impact on the precipitation intensity and patterns. Antecedent soil moisture, steep slopes and roughness will lead to uncertain rainfall-runoff behavior as well. Climate change will usually alter temperature, precipitation intensity and duration along with the runoff timing and magnitude. Various number of studies have proved that urbanization and climate change would have stronger effect on urban rainfall- runoff behavior than other factors. We have reviewed and investigated various and the most effective factors influencing urban runoff generation in this paper. Particularly, the anthropogenic, geomorphologic and meteorological impacts on urban surface runoff have been the focus of this review paper. The study gaps and suggestions for further research have also been discussed at the end. Finally, the best measures to be taken into consideration to mitigate urban excess runoff have been suggested in the final section. [ABSTRACT FROM AUTHOR]

Understanding the temporal variability of the nutrient transport from catchments is essential for planning nutrient loss reduction measures related to land use and climate change. Moreover, observations and analysis of nutrient dynamics in streams draining undisturbed catchments are known to represent a reference point by which human-influenced catchments can be compared. In this paper, temporal dynamics of nitrate-nitrogen (NO3-N) flux are investigated on an event basis by analysing observed lag times between data series. More specifically, we studied lag times between the centres of mass of six hydrological and biogeochemical variables, namely discharge, soil moisture at three depths, NO3-N flux, and the precipitation hyetograph centre of mass. Data obtained by high-frequency measurements (20 min time step) from 29 events were analysed. Linear regression and multiple linear regression (MLR) were used to identify relationships between lag times of the above-mentioned processes. We found that discharge lag time (LAGQ) and NO3-N flux lag time (LAGN) are highly correlated indicating similar temporal response to rainfall. Moreover, relatively high correlation between LAGN and soil moisture lag times was also detected. The MLR model showed that the most descriptive variable for both LAGN and LAGQ is amount of precipitation. For LAGN, the change of the soil moisture in the upper two layers was also significant, suggesting that the lag times indicate the primarily role of the forest soils as the main source of the NO3-N flux, whereas the precipitation amount and the runoff formation through the forest soils are the main controlling mechanisms. [ABSTRACT FROM AUTHOR]

Under global warming, according to results obtained from offline drought indices driven by projections of general circulation models (GCMs), future droughts in China will worsen but the results are not consistent. We analyzed changes in droughts covering the entire hydrologic cycle using outputs of GCMs of the 6th Coupled Model Intercomparison Project (CMIP6) for SSP2-4.5 and SSP5-8.5 climate scenarios, and compared the results with that of popular, offline drought indices [the self-calibrating Palmer Drought Severity Index (scPDSI), Standardized Precipitation Evapotranspiration Index (SPEI) and Standardized Precipitation Actual Evapotranspiration Index (SPAEI)]. Among meteorological, agricultural, and hydrological drought indices tested under both SSP scenarios, the results obtained from SPAEI and scPDSI agree better with univariate drought indices than SPEI. scPDSI generally agrees well with agricultural droughts (Standardized Soil Moisture Index with the surface soil moisture content; SSIS). Future droughts estimated using soil moisture analysis are more widespread than that from precipitation and runoff analysis in humid regions of South China by the end of the twenty-first century. In arid northwestern China and Inner Mongolia, drought areas and severity based on scPDSI and SSIS forced with the SSP scenarios show obvious decreasing trends, in contrast to increasing trends projected in South China. Trends projected using SPEI contradict those projected by other drought indices in non-humid regions. Therefore, selecting appropriate drought indices is crucial in project representative future droughts and provides meaningful information needed to achieve effective regional drought mitigation strategies under climate warming impact. [ABSTRACT FROM AUTHOR]

Earth System Models' complex land components simulate a patchwork of increases and decreases in surface water availability when driven by projected future climate changes. Yet, commonly‐used simple theories for surface water availability, such as the Aridity Index (P/E0) and Palmer Drought Severity Index (PDSI), obtain severe, globally dominant drying when driven by those same climate changes, leading to disagreement among published studies. In this work, we use a common modeling framework to show that Earth System Model (ESM) simulated runoff‐ratio and soil‐moisture responses become much more consistent with the P/E0 and PDSI responses when several previously known factors that the latter do not account for are cut out of the simulations. This reconciles the disagreement and makes the full ESM responses more understandable. For ESM runoff ratio, the most important factor causing the more positive global response compared to P/E0 is the concentration of precipitation in time with greenhouse warming. For ESM soil moisture, the most important factor causing the more positive global response compared to PDSI is the effect of increasing carbon dioxide on plant physiology, which also drives most of the spatial variation in the runoff ratio enhancement. The effect of increasing vapor‐pressure deficit on plant physiology is a key secondary factor for both. Future work will assess the utility of both the ESMs and the simple indices for understanding observed, historical trends. Plain Language Summary: Rivers and groundwater provide almost all water used by humans, and soil moisture is critical for vegetation and crops worldwide. Supercomputer model simulations of rivers, groundwater and soil moisture under future global warming routinely project that some world regions will experience increases in the availability of these resources, while others will experience decreases. Yet the simple formulas that scientists have traditionally relied on to measure climatic "drought" and "aridity" obtain large future decreases in water availability (drying) almost everywhere. This has led to confusion in prior studies and reports. In this study, we resolve this apparent paradox by pinpointing exactly why the supercomputer simulations are less pessimistic than the simple formulas. For rivers and groundwater, the most important reason is that precipitation gets "flashier" and more intense with global warming. For soil moisture, the most important reason is that increasing carbon dioxide allows vegetation to use less water, keeping more water in the soil. Both of these processes are included in the computer models, but not in the simple formulas. This new understanding gives us greater confidence that the computer models are behaving reasonably. Key Points: Community Land Model 5 runoff ratio and soil moisture responses to climate change closely follow the Aridity Index (P/E0) and Palmer Drought Severity Index (PDSI) in a simplified simulationRunoff ratio increases much more than P/E0 in full simulations primarily due to changes in the temporal pattern of precipitationSoil moisture increases more than PDSI in full simulations primarily due to CO2 and vapor pressure deficit effects on plant physiology [ABSTRACT FROM AUTHOR]

Landuse/landcover change (LULCC) and climate change (CC) impacts on streamflow in high elevated catchments are very important for sustainable management of water resources and ecological developments. In this research, a statistical technique was used in combination with the Soil and Water Assessment Tool (SWAT) to the Upstream Area of the Yangtze River (UAYR). Different performance criteria (e.g., R2, NSE, and PBIAS) were used to evaluate the acceptability of the model simulation results. The model provided satisfactory results for monthly simulations in the calibration (R2; 0.80, NSE; 0.78 and PBIAS; 22.3%) and the validation period (R2; 0.89, NSE; 0.75 and PBIAS; 19.1%). Major landuse/landcover transformations from 1990 to 2005 have occurred from low grassland to medium grassland (2%) and wetlands (0.9%), bare land to medium grassland (0.2%), glaciers to wetland (16.8%), and high grassland to medium grassland (5.8%). The results show that there is an increase in average annual runoff at the Zhimenda station in UAYR by 15 mm of, which approximately 98% is caused by climate change and only 2% by landuse/landcover change. The changes evapotranspiration are larger due to climate change as compared to landuse/landcover change, particularly from August to October. Precipitation and temperature have increased during these months. On the contrary, there has been a decrease in evapotranspiration and runoff from October to March which depicts the intra-annual variations in the vegetation in the study area. [ABSTRACT FROM AUTHOR]

Summary: The objective of this research is to investigate the effect of land‐use and climate change on the volume of runoff produced and its impact on water resources. It is clear that the more accurate the assessment of runoff in the future, the better the evaluation of the impact of land‐use and climate changes on water resources. Thus, to more accurately predict water sources in the future, runoff is estimated using two Soil and Water Assessment Tool (SWAT) and SWAT‐DEEP‐IFSO models. The results showed that the SWAT‐DEEP‐IFSO model has a better estimation than the SWAT method. Because Deep Belief Network and an improved optimization algorithm called Improved Fluid Search Optimization (IFSO) algorithm have been utilized in optimizing the hybrid SWAT model that can reduce the error of runoff simulation. After selecting the best model for estimating runoff, the effect of land‐use and climate change is evaluated using different scenarios. Results show that the simulated runoff under the influence of climate and land‐use changes can impact on the average yearly and monthly runoff. These factors have a significant effect on the average yearly runoff changes and are predicted an increasing trend for average yearly runoff. But climate and land‐use changes have a different impact on the different months and for some months of the year the runoff has an increasing trend and for some months the runoff has a decreasing trend. Based on land‐use scenarios, it is found that due to the decrease in rangelands and increase in agricultural lands, there is a possibility of severe floods and drought periods in the region, which reduces the water resources of the study area. [ABSTRACT FROM AUTHOR]

Rainwater harvesting has been known and widely practiced for many centuries, especially during the dry season for a different purpose. The increase of agricultural economy of the country is extremely exposed to weather and climate effects. Decrease of crop production in dry areas is linked to the water (runoff, evaporation and overindulgence use). The objective of this manuscript is to review the status of rainwater harvesting (RWH) technology and practices in sustaining agricultural production in Ethiopia. The in-situ and ex-situ RWH techniques have shown a significant impact on improved soil moisture, runoff and ground water recharge and increased agricultural production, which, in turn, reduce risks and deliver positive impacts on other ecosystems. The implementation of thousands of indicated above structures has been also confined with a range of problems and challenges. In the eastern part of Ethiopia, water shortage and lack of improved technology were the main problems, therefore practicing water harvesting and supplying improved water harvesting technologies providing extended service regularly for farmers should be practiced in the future. Therefore, from the point of view of water conservation, both internal and external catchment-based RWH had the eminent potential of mitigating rainfall-related crop production risks. [ABSTRACT FROM AUTHOR]

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The possibility ofassessing changes in river runofftill 2100 for a number oflarge river basins of the world for a wide range of natural conditions is investigated. The assessment is based on the SWAP (Soil Water-Atmosphere-Plants) model using meteorological data as inputs which were simulated with different general atmosphere-ocean circulation models in accordance with the RCP climate change scenarios. The possible climatic changes in annual runoff for some rivers by the end of the 21st century are compared with the natural interannual variability of river runoff caused by weather noise. [ABSTRACT FROM AUTHOR]

Studies using Drought Hazard Indices (DHIs) have been performed at various scales, but few studies associated DHIs of different drought types with climate change scenarios. To highlight the regional differences in droughts at meteorological, hydrological, and agricultural levels, we utilized historic and future DHIs derived from the Standardized Precipitation Index (SPI), Standardized Runoff Index (SRI), and Standardized SoilWater Index (SSWI), respectively. To calculate SPI, SRI, and SSWI, we used a calibrated Soil andWater Assessment Tool (SWAT) for the Karkheh River Basin (KRB) in Iran. Five bias-corrected Global Circulation Models (GCMs) under two Intergovernmental Panel on Climate Change (IPCC) scenarios projected future climate. For each drought type, we aggregated drought severity and occurrence probability rate of each index into a unique DHI. Five historic droughts were identified with different characteristics in each type. Future projections indicated a higher probability of severe and extreme drought intensities for all three types. The duration and frequency of droughts were predicted to decrease in precipitation-based SPI. However, due to the impact of rising temperature, the duration and frequency of SRI and SSWI were predicted to intensify. The DHI maps of KRB illustrated the highest agricultural drought exposures. Our analyses provide a comprehensive way to monitor multilevel droughts complementing the existing approaches. [ABSTRACT FROM AUTHOR]

In the context of changing climate, this study assessed the effects of global warming on water resources in Tanzania for the mid- 21st century. Climate projections from six global circulation models under the most extreme emission scenario (RCP 8.5) were used as inputs to the soil and water assessment tool (SWAT) to examine the effects. The results were analyzed both at spatial (country-level, watershed-level, and subbasin-level) and temporal (annual and seasonal) scales concerning potential and actual evapotranspiration, surface runoff, water yield, and soil moisture. At the country level, the results showed a 0.8-27.4% increase in annual precipitation, which led to a general increase in evapotranspiration (-2.2-7.3%), surface runoff (12.6-94.1%), water yield (7.5-73.4%), and soil moisture (2.9-20.7%). Watershed-level analysis showed 2.4-31.5%, -2.6-6.8%, 18.4-159.7%, and 3.2-22.8% changes in average precipitation, evapotranspiration, surface runoff, and soil moisture, respectively. While no distinct spatial trend was identified for evapotranspiration and surface runoff, soil moisture was projected to increase in the majority of the areas during both the wet and dry seasons. Probability analysis at the subbasin level showed that less than 15% of the area, during the wet season, experienced decline in precipitation, soil moisture, potential and actual evapotranspiration, surface runoff and water yield, while less than 86% of the country experienced decline during the dry season. Overall, the climate change was found to create a more favorable condition for agricultural production during the wet season by increasing the supply of water, but in the dry season, less favorable conditions were projected. [ABSTRACT FROM AUTHOR]

The factors affecting soil erosion processes are complex and various, comprises two phases: detachment and transport by water. Previous studies indicated that initial moisture content, slope and soil crusts are playing an important role in soil erosion. The primary objectives of this study were to examine the sediment concentration and aggregate size distribution of the washed sediment. Aims were also to create different season specifically modelled situations in order to check runoff rates on bare soils under heavy rainfall. The experiments were conducted with a laboratory-scale rainfall simulator using a 1/2 HH 40 WSQ fulljet nozzle on eutric calcaric Cambisol loamic. Altogether, 72 soil loss samples were collected (6 separate precipitations, 3 time periods, 4 particle size fractions). The experiments indicated that the runoff rate was not increased by the presence of soil crusts, and even less sediment occurs on crusted surfaces. This sediment contained smaller fractions compared to recently tilled surface. The sediment concentration increased with the slope angle, but the runoff rates probably depend rather on the micro-morphology and initial moisture content of the surface. The main erosion process is the raindrop erosion after inland inundation and drought in gentle slopes, while the intermediate period of the precipitation is the most erosive. In general, the ratio of the macro aggregates in soil losses decrease and the ratio of the smaller fractions increase with the time during a precipitation event. Changing climate conditions are shown to have an effect on agricultural production through the temporal and spatial distribution of the erosion rates. [ABSTRACT FROM AUTHOR]

Results from 10 global climate change models are synthesized to investigate changes in extremes, defined as wettest and driest deciles in precipitation, soil moisture and runoff based on each model's historical 20th century simulated climatology. Under a moderate warming scenario, regional increases in drought frequency are found with little increase in floods. For more severe warming, both drought and flood become much more prevalent, with nearly the entire globe significantly affected. Soil moisture changes tend toward drying, while runoff trends toward flood. To determine how different sectors of society dependent on various components of the surface water cycle may be affected, changes in monthly means and interannual variability are compared to data sets of crop distribution and river basin boundaries. For precipitation, changes in interannual variability can be important even when there is little change in the long-term mean. Over 20% of the globe is projected to experience a combination of reduced precipitation and increased variability under severe warming. There are large differences in the vulnerability of different types of crops, depending on their spatial distributions. Increases in soil moisture variability are again found to be a threat even where soil moisture is not projected to decrease. The combination of increased variability and greater annual discharge over many basins portends increased risk of river flooding, although a number of basins are projected to suffer surface water shortages. [ABSTRACT FROM AUTHOR]

Climate change is expected to increase the frequency of flooding events and, thus, the risks of flood‐related mortality and infrastructure damage. Global‐scale assessments of future flooding from Earth system models based only on precipitation changes neglect important processes that occur within the land surface, particularly plant physiological responses to rising CO2. Higher CO2 can reduce stomatal conductance and transpiration, which may lead to increased soil moisture and runoff in some regions, promoting flooding even without changes in precipitation. Here we assess the relative impacts of plant physiological and radiative greenhouse effects on changes in daily runoff intensity over tropical continents using the Community Earth System Model. We find that extreme percentile rates increase significantly more than mean runoff in response to higher CO2. Plant physiological effects have a small impact on precipitation intensity but are a dominant driver of runoff intensification, contributing to one half of the 99th and one third of the 99.9th percentile runoff intensity changes. Plain Language Summary: Floods are one of the most devastating natural disasters in the world, contributing to thousands of deaths and billions of dollars in damages annually. Climate change is expected to increase flood exposure considerably through the 21st century. However, recent studies assessing future flood risk on global scales by downscaling precipitation from Earth system models often neglect important plant physiological responses to rising CO2. In particular, higher CO2 concentrations may lower stomatal conductance and, in the absence of significant plant growth, reduce water loss through transpiration, increasing soil moisture in many regions. For a given precipitation rate, higher soil moisture can decrease the amount of rain that infiltrates the soil and increase runoff. Here we apply a simulation design that isolates the independent effects of higher CO2 on radiatively driven precipitation intensification from plant‐driven soil moisture changes. We show that plant‐physiological responses to increasing CO2 are major drivers of the runoff intensity change in the tropics. Land surface changes contribute to one half of the 99th percentile runoff change and one third of the 99.9th percentile change. Our results suggest that comprehensive flood assessments should account for plant physiology as well as radiative impacts of higher CO2 in order to better inform flood prediction and mitigation practice. Key Points: Plant physiological responses drive a larger increase in the daily intensity of runoff than the annual mean in simulations with rising CO2Plant physiological responses to rising CO2 contribute as much as radiative greenhouse effects to changes in the 99th percentile daily runoffAssessments of future flood risk on global scales should include both atmosphere and land‐driven impacts on rainfall and runoff intensity [ABSTRACT FROM AUTHOR]