Hydrological Processes Of Watershed Research Articles

Hydrological Response to Climate Change: McGAN for Multi-Site Scenario Weather Series Generation and LSTM for Streamflow Modeling

This study focuses on the impacts of climate change on hydrological processes in watersheds and proposes an integrated approach combining a weather generator with a multi-site conditional generative adversarial network (McGAN) model. The weather generator incorporates ensemble GCM predictions to generate regional average synthetic weather series, while McGAN transforms these regional averages into spatially consistent multi-site data. By addressing the spatial consistency problem in generating multi-site synthetic weather series, this approach tackles a key challenge in site-scale climate change impact assessment. Applied to the Jinghe River Basin in west-central China, the approach generated synthetic daily temperature and precipitation data for four stations under different shared socioeconomic pathways (SSP1-26, SSP2-45, SSP3-70, SSP5-85) up to 2100. These data were then used with a long short-term memory (LSTM) network, trained on historical data, to simulate daily river flow from 2021 to 2100. The results show that (1) the approach effectively addresses the spatial correlation problem in multi-site weather data generation; (2) future climate change is likely to increase river flow, particularly under high-emission scenarios; and (3) while the frequency of extreme events may increase, proactive climate policies can mitigate flood and drought risks. This approach offers a new tool for hydrologic–climatic impact assessment in climate change studies.

Enhancing streamflow prediction in the Wujiang River basin: a two-stage decomposition approach with deep learning integration

ABSTRACT Global climate change and human activities have profoundly impacted the geological and hydrological processes in watersheds, increasing the challenges in streamflow prediction. In this study, we propose a streamflow prediction model based on deep learning and dual-mode decomposition specifically tailored for the Wujiang River basin, a significant tributary on the southern bank of the upper Yangtze River. This model effectively addresses the prediction error issue caused by high-frequency components through dual-mode decomposition of time-series data. The results demonstrate that employing the coupled complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN)–variational mode decomposition (VMD)–temporal convolutional network (TCN)–long short-term memory network (LSTM) model reduces prediction errors by at least 35% compared to single decomposition models. Furthermore, compared to individual TCN or LSTM models, the TCN–LSTM coupled model exhibits greater stability and higher prediction accuracy during training, with reductions in mean absolute error and root mean square error by 43.13 and 24.57%, respectively. This model holds promising prospects for application and can provide crucial insights for water resource management.

Metal mobilization from thawing permafrost to aquatic ecosystems is driving rusting of Arctic streams

Climate change in the Arctic is altering watershed hydrologic processes and biogeochemistry. Here, we present an emergent threat to Arctic watersheds based on observations from 75 streams in Alaska’s Brooks Range that recently turned orange, reflecting increased loading of iron and toxic metals. Using remote sensing, we constrain the timing of stream discoloration to the last 10 years, a period of rapid warming and snowfall, suggesting impairment is likely due to permafrost thaw. Thawing permafrost can foster chemical weathering of minerals, microbial reduction of soil iron, and groundwater transport of metals to streams. Compared to clear reference streams, orange streams have lower pH, higher turbidity, and higher sulfate, iron, and trace metal concentrations, supporting sulfide mineral weathering as a primary mobilization process. Stream discoloration was associated with dramatic declines in macroinvertebrate diversity and fish abundance. These findings have considerable implications for drinking water supplies and subsistence fisheries in rural Alaska.

Linking watershed hydrologic processes to connectivity indices on the Loess Plateau, China

Sediment connectivity is an important property influencing landscape evolution. Understanding the link between sediment connectivity and hydrologic processes plays an important role in developing strategies for soil and water conservation measures. Based on 10 years of observations for 30 hydrologically monitored watersheds on the Loess Plateau, measurements for 926 hydrologic events were analyzed and the index of connectivity (IC) was calculated. The high-frequency runoff and sediment data were analyzed, and a normalized hysteresis index (HI) was calculated to assess the dominant hysteresis patterns for each watershed. Correlation analysis was conducted to determine the relationship between IC and HI. The results showed that the watersheds with low IC values were located in regions with dense vegetation and flat terrain and were dominated mainly by a clockwise hysteresis pattern, while the watersheds with high IC values were located in regions with sparse vegetation and steep terrain and were dominated by an anticlockwise hysteresis pattern. The anticlockwise hysteresis pattern was the most frequent and the most efficient type in terms of sediment transport among the 30 watersheds. The anticlockwise hysteresis type was more likely to occur as the IC values increased. A significant negative correlation was observed between the IC values and HI values during small and medium hydrologic events. The link is correlated with the notion that the separation into two components in connectivity indexes are similar to the two sediment sources controlling the hysteresis type. The outcomes from this study are helpful for determining the relationship between sediment connectivity and hydrologic behavior and thus for providing insight into the hydrologic processes that are essential to facilitate sustainable watershed management.

Sensitivity analysis of the flash flood hazard by coupling variable fuzzy method and mutual entropy

AbstractWatershed characteristics are one of the crucial factors affecting watershed hydrologic processes. Watershed hydrologic process regulation has been shown to be an effective tool for flash flood management. This study aims to propose a coupling method to evaluate the flash flood hazard degree of small hilly ungauged watersheds based on their watershed characteristic factors and identify sensitive factors influencing flash flood hazard. In this regard, nine watershed characteristic factors were selected for flash flood hazard sensitivity analysis. The variable fuzzy method (VFM) was proposed to calculate the eigenvalue of flash flood hazard degree for each small hilly watershed, and mutual entropy was proposed to identify sensitive factors influencing hazard degree. As an example, the sensitive factors in Licheng County with 119 small hilly watersheds in China are identified and further verified by stepwise regression analysis, which are mean watershed slope, soil moisture, average width of the mainstream, and watershed shape factor. This study shows that VFM and mutual entropy can be used jointly to identify the sensitive factors associated with the flash flood hazard in small hilly ungauged watersheds. The results can be used for engineering measure management in flash flood hazard control.

Attribution Analysis of Runoff Variation in the Yue River Watershed of the Qinling Mountains

In recent decades, global climate change, especially human activities, has led to profound changes in the hydrological cycle and hydrological processes in watersheds. Taking the Yue River watershed in the Qinling Mountains in China as the study area, the Mann–Kendall test and Pettitt mutation test method were used to analyze the various characteristics of hydrological and climatic elements from 1960 to 2018. Then, the elastic coefficient method based on the Budyko framework was used to estimate the elastic coefficient of runoff change on each influencing factor. The results showed that the annual runoff decreased at a rate of 0.038 × 108 m3/a ( P > 0.05 ), and a significant abrupt change occurred in 1990. The annual precipitation and potential evapotranspiration (ET0) increased and decreased, with change rates of 0.614 mm/a and −0.811 mm/a ( P > 0.05 ), respectively. The elasticity coefficients of precipitation, ET0, and the underlying surface were 1.95, −0.95, and −0.85, respectively, indicating that annual runoff was most sensitive to the change in precipitation, followed by the change in ET0, and had the lowest sensitivity to the change in the underlying surface. Underlying surface change is the main factor of runoff decrease; the contribution is 89.07%. The total contribution of climate change to runoff change is 10.93%, in which the contributions of precipitation and ET0 are 17.59% and −6.66%, respectively. The NDVI reflecting underlying surface change has been increasing since 1990, which is an important reason for the runoff decrease.

Event Based Post-Fire Hydrological Modeling of the Upper Arroyo Seco Watershed in Southern California

Understanding, development and integration of pre-fire and post-fire watershed hydrological processes into a watershed hydrological model in a wild-fire repeating region similar to parts of California is critical for emergency assessments. 95% of the upper Arroyo Seco watershed located in Los Angeles County in southern California was burned by the Station fire that occurred in August 2009, significantly increasing the watershed observed runoff. This watershed was employed to develop the January 2008 rainfall runoff model as a pre-fire event-based watershed hydrological model. This pre-fire watershed model was subsequently employed in the rainfall events of 18 January 2010 and 27 February 2010, a few months after the fire event of August 2009. The pre-fire watershed model when employed in the post-fire rainfall events without considering the fire effects vastly underestimated the simulated discharge. For this reason, in this study of the post-fire catchment runoff modeling the following points are taken into consideration: (a) a realistic distributed initial soil moisture condition; (b) a formulation that includes a reduction factor and a burn severity factor, as multiplying factors to soil hydraulic conductivity in the soil characteristic curve; and (c) runoff routing parameterization under burned conditions. Developing the post-fire Arroyo Seco watershed model by using the above-mentioned points enhanced the Nash–Sutcliffe Efficiency from −24% to 82% for the 18 January 2010 rainfall event and from −47% to 96% for the 27 February 2010 rainfall event.

Sensitivity and Performance Analyses of the Distributed Hydrology–Soil–Vegetation Model Using Geomorphons for Landform Mapping

Landform classification is important for representing soil physical properties varying continuously across the landscape and for understanding many hydrological processes in watersheds. Considering it, this study aims to use a geomorphology map (Geomorphons) as an input to a physically based hydrological model (Distributed Hydrology Soil Vegetation Model (DHSVM)) in a mountainous headwater watershed. A sensitivity analysis of five soil parameters was evaluated for streamflow simulation in each Geomorphons feature. As infiltration and saturation excess overland flow are important mechanisms for streamflow generation in complex terrain watersheds, the model’s input soil parameters were most sensitive in the “slope”, “hollow”, and “valley” features. Thus, the simulated streamflow was compared with observed data for calibration and validation. The model performance was satisfactory and equivalent to previous simulations in the same watershed using pedological survey and moisture zone maps. Therefore, the results from this study indicate that a geomorphologically based map is applicable and representative for spatially distributing hydrological parameters in the DHSVM.

Effects of land-use data resolution on hydrologic modelling, a case study in the upper reach of the Heihe River, Northwest China

Land-use/land-cover (LULC) data represent important inputs in hydrologic models. The LULC data can affect modelled watershed hydrologic processes by altering the rates of interception, infiltration, evapotranspiration and groundwater recharge that govern the timing and volume of surface and river runoff. A thorough understanding of the impacts of LULC resolution on hydrologic modelling is thus essential and important. Generally, differences in the resolution of LULC data in hydrologic modelling can result in different interpretation accuracies, LULC classifications and spatial resolutions for one-year LULC datasets; typically, such models only use one-year LULC datasets in the simulation period to simply the calculation process. But how would the model performance change if multiple years of LULC data were input into hydrologic models? To better understand the impacts of LULC resolution on hydrologic modelling, this study input four LULC datasets into the SWAT (Soil and Water Assessment Tool) model and compared the impacts of the LULC datasets on the hydrologic modelling results for a high-elevation, cold and mountainous watershed in Northwest China. The first three datasets describe the LULC in the year 2000 and are based on different interpretation accuracies, LULC classifications and spatial resolutions. The last dataset is the yearly LULC data over a 20-year period. To incorporate the yearly LULC dataset, we modified the HRU (hydrologic response unit) division method and SWAT computational structure. The main findings were as follows. (1) A yearly LULC dataset may result in a higher simulation complexity in the SWAT model because this involves the most LULC patches. (2) If multiple years of LULC data exist, a LULC dataset with smaller time intervals, e.g. yearly is necessary in streamflow modelling in SWAT to get better model performance, the model performance may improve by 2.2%–13.9% compared to one-year LULC datasets. (3) If only one-year LULC datasets exist, we suggest inputting a dataset with a high resolution and remote sensing interpretation accuracy and reduced numbers of LULC classification types into SWAT to improve the hydrologic model performance; with such an approach, the model performance may improve by 1.1%–6.9% compared to other one-year LULC datasets.

Modeling Tropical Cyclone Induced Stream Flow in Tar Pamlico River of North Carolina

ABSTRACT In order to better understand and simulate large coastal watershed hydrology and hydro-meteorological processes associated with tropical cyclone (TC) induced inland flooding, the Annualized Agricultural Nonpoint source pollution Model (A nn AGNPS) with Muskingum channel routing has been applied to the Tar-pamlico river basin in North Carolina, USA. The study focuses on three major hydro-meteorological processes: 1) large-scale atmospheric environment, 2) watershed hydrological processes and 3) groundwater response. The modeling results indicate that although the AnnAGNPS model can perform well in predicting the total amount of watershed runoff, channel routing is needed to improve the hydrographs of flow discharge during hurricane events. Sensitivity analysis of soil saturated hydrological conductivity ( K s ) indicates that both base flow and event total runoff are sensitive to K s . Base flow increases as K s increases when 0 K s ≤ 15 m/day, but decreases slightly when K s > 15 m/day. Peak runoff exponentially decreases as K s increases. The results also show that without the preceding Hurricane Dennis, the outlet discharge as a result of Hurricane Floyd would have been as much as 37% lower than that caused by the combined Dennis-Floyd effect.

Исследование лесогидрологических процессов на водосборах рек бассейна Амура по данным спутниковых и гидрометеорологических наблюдений

Исследование лесогидрологических процессов на водосборах рек бассейна Амура по данным спутниковых и гидрометеорологических наблюдений

Water Quality Assessment and Application of SWAT Model for Hydrologic Simulations in a Mined Watershed

This paper explored the application of Soil and Water Assessment Tool in modelling hydrological processes of opencast mined affected Olidih watershed of Jharia coalfield region in India. The effect of opencast mines on hydrological processes of watershed was also analysed. Daily streamflow and sediment yield data of years 2005–2006 were used for calibration and 2007–2008 for validation. Model performance was quite satisfactory during calibration and validation. The potential influences of mines were assessed by modelling an alternative scenario assuming nomines (unmined) for the period 2005–2010. Abandoned opencast mines altered the magnitude of hydrological processes of Olidih watershed. Increase in sediment yield by 14.29%, groundwater flow by 13%, evapotranspiration by 4% and decrease in surface runoff by 51.33% and water yield by 6% was observed as compared with no-mines scenario. Water samples from study area were collected and analysed to identify their suitability for domestic uses in pre-monsoon (PRM) and post-monsoon (POM) seasons. The results showed that surface water from 53.6% mineaffected area in PRM and 28.2% mine-affected area in POM season was not suitable for drinking purpose.

Modeling the effects of the streamflow changes of Xinjiang Basin in future climate scenarios on the hydrodynamic conditions in Lake Poyang, China

The responses of lake hydrodynamics to the hydrological processes in watersheds have been associated with the ecological evolution of and the biochemical processes in aquatic ecosystems. This paper investigates how the changes in the streamflow of Xinjiang Basin in different future climate scenarios could affect the hydrodynamic conditions in Lake Poyang. First, the hydrodynamic processes in Lake Poyang (i.e., lake level and water velocity) were simulated based on the environmental fluid dynamics code (EFDC). Error statistics indicated that the hydrodynamic model reasonably reflected the hydrodynamics in Lake Poyang. Second, the future streamflow of Xinjiang Basin from 2016 to 2050, which was projected in two future climate scenarios (Sim_RCP4.5 and Sim_RCP8.5) based on the Xin’anjiang model, was applied to hydrodynamic modeling to investigate the relationship between future discharge and hydrodynamics. Results showed that the streamflow changes of Xinjiang Basin in future climate scenarios considerably affected the seasonal distribution of the flow field in Lake Poyang. The hydrodynamic change region that exceeded the threshold values under these two climate scenarios both demonstrated a fluctuating trend and nearly covered the entire lake until April. In Sim_RCP8.5 a slightly larger area was influenced than in Sim_RCP4.5, except in January, and the eastern channel was always significantly affected by streamflow change. These analyses can enhance the present understanding of the relationships between the hydrodynamics in lakes and the hydrological processes of sub-basins.

Application of run-off model as a contribution to the torrential flood risk management in Topčiderska Reka watershed, Serbia

This paper deals with developing of hydrological flow model for the torrential watershed of the Topciderska River, located in the Belgrade macro-region, in which torrential flood events have had destructive human and material consequences. The aim of the paper was to show that model, developed by hydrological software SHETRAN, is useful tool enabling the simulation of physical properties and hydrological processes in watersheds, having a significant place in decision support system within the torrential flood risk management. Results achievement was enabled through three phases: (1) Sensitivity analysis showed that the closest hydrograph to registered hydrograph is modelled with averaged values of parameters; (2) model calibration was done by calibration of four main parameters with significant influence on flow component (hydraulic conductivity of soil and rock, Strickler roughness coefficient for overland and river network flow) in case of the torrential flood event from 10th July 1999; and (3) model verification was done by input of calibrated values in case of two another torrential flood events (1996, 1999). Statistical analysis of correspondence of modelled and registered discharges showed that due to correlation coefficient (0.95–0.98) and determination coefficient (0.90–0.96) as well as probability of error according to F test, good results are achieved. Considering obtained results, developed model should be a part of torrential flood risk management in watershed of Topciderska River.

Using object oriented technique to extract jujube based on landsat8 OLI image in Jialuhe Basin

Vegetation is a crucial factor that affects watershed hydrological processes. To understand the effect of jujube vegetation variation on streamflow in the Jialuhe River Basin, jujube forest was investigated in this study. Object-oriented classification technique was used to extract jujube characteristics. The primary vegetation types were selected to sample the reflectance, and the spectral response curves were obtained. Then, the rule set of decision tree is constructed based on the comprehensive analysis of the image information and the object type. The classification results show that jujube forest is scattered and mainly distributed in the lower reaches. The area of jujube forest is 8.8 km2, which accounts for about 7.8% of the total area.

Simulation of Green and Blue Water Impacts Caused by Climate Changes in the Apucaraninha River Watershed, Southern Brazil (Simulação dos Impactos da Água Verde e Azul Causados pelas Mudanças Climáticas na Bacia Hidrográfica do Rio Apucaraninha...)

Climate changes may generate significant impacts in the hydrological cycle. It is important to recognize modifications in green water (water stored in soil followed by the consumption of the vegetation) and blue water (water that flows into rivers, lakes, wetlands and shallow aquifers) availability in consequence of climate change modifications. The mathematical modelling is used to simulate the effect of climate change scenarios in hydrological processes in watersheds. This study aimed to evaluate the impacts of climate change in blue and green water in Apucaraninha River Watershed, Southern Brazil, considering the climate scenarios A2 and B2, pessimistic and optimistic, respectively, about greenhouse gases emissions developed by IPCC. SWAT was calibrated and validated using daily streamflow from 1987 to 2012. Climate scenarios A2 and B2 were used to simulate the hydrological conditions for the period 2071-2100. The model presented satisfactory fit compared to the observed data allowing the simulation of the current hydrological conditions, therefore permitting the simulation of future climate change impacts on green and blue water. We found that despite the increase in potential evapotranspiration of 19% and 12% for A2 and B2 scenario respectively, caused by the increase in temperature, the reduction in rainfall amount induced to a reduction in actual evapotranspiration, which correspond to green water, and a reduction of 1% for A2 scenario and 14% for B2 scenario in blue water availability.

Effects of wildfires on peak discharges in watersheds

Wildfires can alter the hydrological processes in watersheds resulting in increases in peak discharge - one of the most important hydrological variables used in water resources applications. It thus follows that the standard methods used to calculate rainfall runoff should be modified in order to model the potential changes in watershed response under post-fire conditions. However, no reliable methodology for quantitatively assessing the effects of wildfires on hydrological parameters, such as curve numbers or runoff coefficients, has been identified to date. The approaches currently used are usually site-specific, mainly based on personal experience or very simple empirical strategies and then affected by a degree of uncertainty. This paper addresses issues regarding the estimation of the Soil Conservation Service Curve Number (SCS-CN or CN) and considers the case study of San Giuliano, L’Aquila (Italy), a small urban basin recently affected by a wildfire that resulted in a significant reduction in forest cover. The effects of the fire on runoff are modelled by adjusting CNs according to existing approaches from the literature in order to perform a sensitivity analysis for post-fire conditions; this allows us to examine the effects of the variability in model input parameters (estimates of post-fire CNs) upon expected peak discharges related to different return period storms. The fire effect ratio, which can be seen as a global parameter for describing alterations in the watershed response due to fire, is calculated by dividing post-fire peak discharge by pre-fire peak discharge. For the present case study, this ratio ranged between 1.1 and 2.3, indicating the urgent need for quantitative research on the effects of wildfires on the hydrological variables affecting runoff calculations.

Integrated climate and land use change scenarios for California rangeland ecosystem services: wildlife habitat, soil carbon, and water supply

Context In addition to biodiversity conservation, California rangelands generate multiple ecosystem services including livestock production, drinking and irrigation water, and carbon sequestration. California rangeland ecosystems have experienced substantial conversion to residential land use and more intensive agriculture. Objectives To understand the potential impacts to rangeland ecosystem services, we developed six spatially explicit (250 m) climate/land use change scenarios for the Central Valley of California and surrounding foothills consistent with three Intergovernmental Panel on Climate Change emission scenario narratives. Methods We quantified baseline and projected change in wildlife habitat, soil organic carbon (SOC), and water supply (recharge and runoff). For six case study watersheds we quantified the interactions of future development and changing climate on recharge, runoff and streamflow, and precipitation thresholds where dominant watershed hydrological processes shift through analysis of covariance. Results The scenarios show that across the region, habitat loss is expected to occur predominantly in grasslands, primarily due to future development (up to a 37 % decline by 2100), however habitat loss in priority conservation errors will likely be due to cropland and hay/pasture expansion (up to 40 % by 2100). Grasslands in the region contain approximately 100 teragrams SOC in the top 20 cm, and up to 39 % of this SOC is subject to conversion by 2100. In dryer periods recharge processes typically dominate runoff. Future development lowers the precipitation value at

鄱阳湖湿地降水氢氧稳定同位素特征分析

大气降水是水文循环的重要环节，对降水氢氧稳定同位素的研究有利于揭示水循环规律、推断水汽来源，进而可深入分析流域水文过程。本文收集2013年11月~2014年5月鄱阳湖湿地降水样品，采用MAT253同位素比质谱仪连接Flash EA/HT对该地区降水氢氧稳定同位素进行测定，分析了其组成特征；并结合研究区气象观测数据，研究了降水中δ18O与氘盈余的变化规律。结果表明，鄱阳湖湿地大气降水线方程δD = 8.99δ18O + 11.52的斜率、截距均大于全球及我国大气降水线的平均水平，符合该地区湿润多雨的气候特点。δ18O与降水量呈显著负相关关系，表现为“降水量效应”，而温度效应在季风气候的影响下受到一定的抑制。氘盈余值受冬夏季风的影响，呈现出冬高夏低的季节性变化规律，与我国东部季风区的变化特征相符；影响氘盈余值的主要因素为相对湿度，两者呈显著负相关关系。 Precipitation is an important part of hydrologic cycle. Study on stable hydrogen and oxygen isotopes is advantageous to reveal the laws of water circulation and infer vapor source for further analysis of wa-tershed hydrological processes. We collected the samples of rainfall in Poyang Lake wetland from No-vember 2013 to May 2014, measured oxygen 18 and deuterium by using MAT253 IRMS connecting with Flash EA/HT and analyzed the characteristics of stable isotopes afterwards. In addition, factors affecting and deuterium excess with the meteorological data of Poyang lake wetland were discussed. The results show that the local meteoric water line is fitting the equation: δD = 8.99δ18O + 11.52, which the slope and intercept are above the average level of the Global and National Meteoric Water Line, is according with the characteristic of humid and rainy climate in the region. A significant negative correlation called “pre-cipitation effect” between oxygen 18 and precipitation is indicated. In contrast, temperature effect is re-strained under the influence of monsoon climate. Deuterium excess shows the obvious seasonal variation: deuterium excess is higher in winter than in summer which conforms to the laws in monsoon area in eastern China. Moreover, the main influencing factor is mean relative humidity which showed a negative correlation with deuterium excess.

Drought variation trends in different subregions of the Chinese Loess Plateau over the past four decades

In this study, we analyzed the drought variation trends in six subregions of the Loess Plateau over the past four decades. To do this, we used a new method wherein we combined the Variable Infiltration Capacity (VIC) Model for simulating watershed hydrological processes and Palmer Drought Severity Index (PDSI) for drought assessment and analysis. A new classified calibration procedure of climate characteristic coefficient, Kj, was introduced in the study to improve the traditional PDSI computation method. The results suggest that the total area affected by drought in subregions 1–3 located in the middle reaches of the Yellow River mainly exhibited downward trends during 1971–2010. As these domains are the principal sediment sources of the Yellow River, the decreasing trends in drought area could benefit to vegetation recover in these regions, which are key sites of “Grain for Green” project, and help to control the severe soil and water losses. However, subregions 4–6 located in the upper reaches of the Yellow River primarily experienced upward trends in the total drought area. These subregions are the main grain producing areas of the study region, and the increase in drought area may cause damage to agricultural production and regional food security. The spatial distribution of drought frequency increased from southeast to northwest on the Loess Plateau. Most areas of the subregions 4–6 of the plateau exhibited an upward trend in drought frequency as indicated by a Mann–Kendall test, and the upward trend will show persistent behavior in the future, according to a Hurst exponent analysis. Generally speaking, the drought hazard in the upper reaches of the Yellow River tended to be increasingly severe, while drought hazard in the middle reaches has relieved to certain extent over the past four decades.