Search

Steady glacier runoff is related to the security and resilience of water resources in meltwater recharge basins, so the status and change of glaciers and their response to climate change in the upper reaches have received widespread concerns. Here, the spatiotemporal characteristics of glacier wastage in the Upper Reaches of Shule River Basin (URSRB) driven by climate change were analyzed based on multi-source and multi-temporal remotely sensed images. Firstly, we extracted multi-temporal glacier outlines from the Landsat time series data using Google Earth Engine (GEE) for seven different periods every approximately 5 years from 1990 to 2020. The spatiotemporal analysis of URSRB glaciers demonstrates a sustained reduction in glacier area from 481.07 ± 24.24 km 2 in 1990 to 384.05 ± 22.71 km 2 in 2020, corresponding to a glacier shrinkage rate of - 0.67 ± 0.23%/year, characterized by considerable temporal variability. Secondly, multi-temporal DEMs derived from ASTER stereo imagery spanning from 2000 to 2020 were used to compute the glacier surface elevation changes and determine the glacier mass loss. The overall glacier surface elevation change rate was - 0.32 ± 0.14 m/year, equivalent to a mass balance of - 0.28 ± 0.12 m w.e./year. Lastly, to better apprehend the long-term response of URSRB glaciers to climate change, studies on climate change were carried out based on the EAR5-Land reanalysis dataset. The long-term trend of glacier wastage is attributed to the increase in summer temperature, and the negative effects of increased summer temperature on glaciers exceeded the positive effects of increased annual precipitation. In summary, glaciers in the URSRB have experienced a significant area reduction and accelerated mass loss against the backdrop of climatic warming and humidification., (© 2024. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

As the hydrologic buffering capacity of glaciers diminishes on climate warming, groundwater stored in the glaciated alpine watersheds becomes an important source of streamflow, quantifying the groundwater contribution to this streamflow is significant for better predictions of the impact of rapidly disappearing glaciers on regional water resources. However, the role of groundwater in sustaining streams remains unclear. Here, we selected the upper Shule River Basin (USRB) on the northeast Tibetan Plateau (NETP) as a case to address this knowledge gap through a comprehensive study of geochemistry and stable isotopes data, the application of an end member mixing model and the baseflow hydrograph separation program (HYSEP). Our results indicate that even though the potential sources of streamflow exhibited distinct monthly differences during December 2012-December 2013, the groundwater was the dominant contributor to streamflow generation in the USRB. The groundwater contributed 45% to 100% of the monthly mean streamflow, and the annual mean value of 70%. By contrast, the glacier-snow meltwater and precipitation only contributed 12% and 18% of the annual discharge. The volume contributed by groundwater was calculated as 9.93 × 10 8 m 3 , approximately six times higher than the input of the glacier-snow meltwater (i.e., 1.63 × 10 8 m 3 ). From 1954 to 2018, the volume of the groundwater discharge to the streamflow in the USRB continuously increased from 4.83 × 10 8 m 3 /a (65% of total streamflow) in the 1950s to 10.34 × 10 8 m 3 /a (71% of total streamflow) in the 2010s, an increase of 2.14 times. The retreating glacier, as well as increasing precipitation and temperature, were determined to be the main reasons for the increase in groundwater discharge to the streamflow. Our findings suggest that groundwater contribution is more important than was previously thought in the glaciated alpine watersheds on the NETP., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Terrestrial evapotranspiration (ET a ) reflects the complex interactions of climate, vegetation, soil and terrain and is a critical component in water and energy cycles. However, the manner in which climate change and vegetation greening influence ET a remains poorly understood, especially in alpine regions. Drawing on the Global Land Evaporation Amsterdam Model (GLEAM) ET a data, the interannual variability of ET a and its ties to precipitation (P), potential evaporation (ET p ) and vegetation (NDVI) were analysed. The Budyko framework was implemented over the period of 1982 to 2015 to quantify the response of ET a to climate change's direct (P and ET p ) and indirect (NDVI) impacts. The ET a , P, ET p and NDVI all showed significant increasing trends from 1981 to 2015 with rates of 1.52 mm yr -1 , 3.18 mm yr -1 , 0.89 mm yr -1 and 4.0 × 10 -4  yr -1 , respectively. At the regional level, the positive contribution of increases in P and NDVI offset the negative contribution of ET p to the change in ET a (∆ET a ). The positive ∆ET a between 1982 and 2001 was strongly linked with the concomitant increase in NDVI. Increases in vegetation contributing to a positive ∆ET a differed among landscape types: for shrub, meadow and steppe they occurred during both periods, for alpine vegetation between 1982 and 2001, and for desert between 2002 and 2015. Climate change directly contributed to a rise in ET a, with P as the dominant factor affecting forested lands during both periods, and alpine vegetation between 2002 and 2015. Moreover, ET p was a dominant factor for the desert between 1982 and 2001, where the variation of P was not significant. The contributions of factors having an impact on ∆ET a are modulated by both the sensitivity of impact factors acting on ET a as well as the magnitudes of factor changes. The greening of vegetation can influence ET a by increasing vegetation transpiration and rainfall interception in forest, brush and meadow landscapes. These findings can help in developing a better understanding of the interaction of ecosystems and hydrology in alpine regions., Competing Interests: Declaration of competing interest The authors declare no competing financial interests., (Crown Copyright © 2020. Published by Elsevier B.V. All rights reserved.)

Under the influence of climate change, the hydrological processes of glaciers have undergone significant changes, a fact which is seriously affecting agricultural production in the downstream region of the Tianshan Mountains, China. In order to explore the intrinsic relationship between climate change and hydrological elements, we proposed an "evaluation-driving-prediction" system to study it. First, we constructed a glacier-enhanced soil and water assessment tool model (GE-SWAT) and used a two-stage calibration method to optimize the model parameters. Next, a scenario analysis was used to evaluate the driving factors of historical runoff changes. Finally, we projected future runoff changes using bias-corrected regional climate model (RCM) outputs. The results of the case study on the Jinghe River Basin in the Tianshan Mountains show that from 1963 to 2016, total runoff increased by 13.3%, 17.7% of which was due to increasing precipitation and 1.8% of which was negated by rising temperatures. The glacier runoff increased by 14.5%, mainly due to the rising temperatures. A 3.4% reduction in snowmelt was caused by a lower snowfall/precipitation ratio, which significantly reduced the snowfall from June to August. The RCM projection indicated that the warming and humidification phenomenon in the study area will continue at least through to the mid-21st century. A consistent increase in glacier runoff and total runoff is projected, but the contribution rate of the glacier runoff will have little to no change under the RCP4.5 and RCP8.5 emission scenarios. Our research demonstrates the simulation performance of the GE-SWAT model in a basin with moderate glacier cover. This method is shown to be efficient in quantifying the impact of climate change on glacier hydrological processes and predicting future streamflow changes, providing a good research reference for similar regions. [ABSTRACT FROM AUTHOR]

Derived from realistic global warming scenarios, long‐term projections of spatial patterns in precipitation and temperature in hydrology and climatology can serve to evaluate climate risk, explore sources of renewable energies and allow local‐scale data to inform decisions regarding agricultural, ecosystem, social, recreational and economic activities. Under the CORDEX‐EA project, the precipitation and temperature projections (2020–2045) for the economically and socially important region of Northwestern China were derived from high‐resolution regional climate model (RCM) simulations for RCP 4.5 and 8.5 scenarios, and compared against a historical period or baseline of 1980–2005. Drawing data from four key RCMs [Weather Research and Forecasting (WRF); Regional Spectral Model (RSM); Regional Climate Model version 4.0 (RegCM4); Mesoscale Model version 5 (MM5)], reliable local‐scale projections were generated by applying suitable bias correction that accords with the multivariate bias correction (MBC) approach. To validate this approach and then evaluate climate change impacts, the adjusted precipitation and temperature estimated from bias‐corrected models for the historical period were compared to the observed data. The results showed that the simulated spatiotemporal distribution of multiyear average precipitation and temperature appear to fit relatively well with the observations, however, the wet‐cold and dry‐warm climate‐related biases were still evident for the high altitude regions. Bias‐corrected future projections of RCMs indicated spatially averaged annual precipitation is expected to rise by about 23.6 and 35.3 mm under the RCP 4.5 and 8.5 scenarios, respectively, while spatially averaged annual temperature is expected to rise by about 1.95 and 1.10°C. Precipitation is projected to increase in all seasons, albeit, more so in the cold season (i.e., boreal winter and spring) than the warm season (i.e., boreal summer and autumn). The annual increase is expected to be about 56.7% under the RCP 4.5 scenario, compared to 67.6% under the RCP 8.5 scenario. The changes of mean temperature in winter are expected to be significant, −37.8% under both RCP scenarios. For spring, the mean temperature will rise by 23.1% (28.9%) under the RCP 4.5 (8.5) scenario. A MBC approach was found to be effective in yielding reliable projected changes in precipitation and temperature variables. The proposed approach has important implications for climatological studies and evaluation of climate change impacts on localized regions, not only in China, but also in other similar areas of the world, where decisions for managing climate risk must be implemented by policy makers, government, industry and stakeholders. [ABSTRACT FROM AUTHOR]

Assessment of the effects of climate change and land use/cover change (LUCC) on the flow regimes in watershed regions is a fundamental research need in terms of the sustainable water resources management and ecosocial developments. In this study, a statistical and modeling integrated method utilizing the Soil and Water Assessment Tool (SWAT) has been adopted in two watersheds of northeastern Tibetan Plateau to separate the individual impacts of climate and LUCC on the flow regime metrics. The integrated effects of both LUCC and climate change have led to an increase in the annual streamflow in the Yingluoxia catchment (YLC) region and a decline in the Minxian catchment (MXC) region by 3.2% and 4.3% of their total streamflow, respectively. Climate change has shown an increase in streamflow in YLC and a decline in MXC region, occupying 107.3% and 93.75% of the total streamflow changes, respectively, a reflection of climatic latitude effect on streamflow. It is thus construed that the climatic factors contribute to more significant influence than LUCC on the magnitude, variability, duration, and component of the flow regimes, implying that the climate certainly dominates the flow regime changes in northeastern Tibetan Plateau. [ABSTRACT FROM AUTHOR]

Climate change and land use/cover change (LUCC) are two factors that produce major impacts on hydrological processes. Understanding and quantifying their respective influence is of great importance for water resources management and socioeconomic activities as well as policy and planning for sustainable development. In this study, the Soil and Water Assessment Tool (SWAT) was calibrated and validated in upper stream of the Heihe River in Northwest China. The reliability of the SWAT model was corroborated in terms of the Nash-Sutcliffe efficiency (NSE), the correlation coefficient (R), and the relative bias error (BIAS). The findings proposed a new method employing statistical separation procedures using a physically based modeling system for identifying the individual impacts of climate change and LUCC on hydrology processes, in particular on the aspects of runoff and evapotranspiration (ET). The results confirmed that SWAT was a powerful and accurate model for diagnosis of a key challenge facing the Heihe River Basin. The model assessment metrics, NSE, R, and BIAS, in the data were 0.91%, 0.95%, and 1.14%, respectively, for the calibration period and 0.90%, 0.96%, and −0.15%, respectively, for the validation period. An assessment of climate change possibility showed that precipitation, runoff, and air temperature exhibited upward trends with a rate of 15.7 mm, 6.1 mm, and 0.38 °C per decade for the 1980 to 2010 period, respectively. Evaluation of LUCC showed that the changes in growth of vegetation, including forestland, grassland, and the shrub area have increased gradually while the barren area has decreased. The integrated effects of LUCC and climate change increased runoff and ET values by 3.2% and 6.6% of the total runoff and ET, respectively. Climate change outweighed the impact of LUCC, thus showing respective increases in runoff and ET of about 107.3% and 81.2% of the total changes. The LUCC influence appeared to be modest by comparison and showed about −7.3% and 18.8% changes relative to the totals, respectively. The increase in runoff caused by climate change factors is more than the offsetting decreases resulting from LUCC. The outcomes of this study show that the climate factors accounted for the notable effects more significantly than LUCC on hydrological processes in the upper stream of the Heihe River. [ABSTRACT FROM AUTHOR]

This paper presents a detailed analysis of how future climate change may affect water availability in a typical arid endorheic river basin, the Heihe River basin (HRB), in northwest China. The analysis is based on the improved Soil Water Assessment Tool (SWAT), which is calibrated and validated with historical streamflow data from the upper HRB and is used to predict future hydrological responses. Six general circulation models (GCMs), under two emission scenarios (RCP4.5 and RCP8.5), are downscaled to construct future climate change scenarios. The results suggest that the climate of the upper HRB will likely become warmer and wetter in the near future (2021-50), with the largest increase in precipitation occurring in the summer. Correspondingly, the basinwide evapotranspiration, snowmelt, and runoff are projected to increase over the same period. The mean temperature in the near future is projected to rise, relative to the recent 30 years (1981-2010), by 1.2°-1.7°C under scenario RCP4.5 and by 1.4°-2.1°C under scenario RCP8.5. The mean precipitation is projected to increase by 10.0%-16.6% under scenario RCP4.5, and by 10.5%-22.0% under scenario RCP8.5. The mean values of evapotranspiration, snowmelt, and runoff are expected to increase by 14.2%, 4.3%, and 11.4%, respectively, under scenario RCP4.5 and to increase by 18.7%, 5.8%, and 12.8%, respectively, under scenario RCP8.5. Though the model simulations forecast an increase in streamflows in the headwater region of the HRB, future water availability varies significantly over space and time. The findings of this study will help to frame more effective water management strategies for the HRB under changing climatic conditions. [ABSTRACT FROM AUTHOR]

Through its effects on water and energy cycles, elevation plays an important role in modulating the spatial distribution of climatic changes in mountainous regions. A key hydrological indicator, reference evapotranspiration (ET0) reflects the maximum amount of water transferred to the atmosphere from the land surface. The current scarcity of information regarding elevation's impact on variation in ET0 under climate change limits our understanding of the extent to which elevation modulates interactions between ET0 and climate change and of the attendant processes involved. Drawing upon long-term (1960–2017) meteorological observations from 84 stations in Northwest China (NWC), we examined (i) spatial and temporal variations in ET0; (ii) the sensitivity and contribution of air temperature (T), sunshine duration (SD), relative humidity (RH), and wind speed (WS) to ET0; (iii) the existence of a relationship between elevation and ET0 trends; and (iv) the major factor in controlling this relationship by using attribution analysis. Overall, annual ET0 in NWC showed a declining trend between 1960 and 2017, though at a change point in 1993, the trend shifted from a decline to a rise. A significant correlation between temporal change in ET0 and elevation confirmed the existence of a relationship between elevation and ET0 variation. The effect of elevation on changes in ET0 depended mainly on the elevation-based tradeoff between the contributions of T and WS: WS was the primary factor contributing to the decrease in ET0 below 2000 m, and T was the dominant factor contributing to the increase of ET0 above 2000 m. The rate of reduction in WS declined as elevation increased, thereby diminishing its contribution to variation in ET0. The present study's results can serve to guide agricultural irrigation in different elevation zones under NWC's evolving climatic conditions. [ABSTRACT FROM AUTHOR]

• The GPP-Budyko framework was improved by considering basin water storage change at growing season scale. • The attribution method of GPP change was proposed under this framework. • The increasing growing season GPP was primarily controlled by human activities in the IRB-NWC. The Budyko framework has been successfully used to evaluate variations in hydrological processes and their responses to climate change and human activity. Recently, this framework was extended to estimate the mean annual terrestrial gross primary productivity (GPP) by defining two GPP potentials and a control parameter (n). However, the feasibility of the GPP–Budyko framework at the growing season scale has not been validated and an attribution analysis of GPP changes under this framework has not been conducted. Therefore, focusing on 18 inland river basins of Northwestern China (IRB–NWC), the GPP–Budyko framework was improved by considering basin water storage change, and its adaptability was validated at the growing season scale. Furthermore, the impacts of climate change and human activity on the growing season GPP were quantified using an elasticity analysis approach. The results showed that the improved Budyko framework effectively captured the effect of vital climatic constraints on the growing season GPP. The control parameter n increased in most basins from 1982 to 2018. Additionally, the mean growing season GPP was 88.46 gC m −2 with an increasing rate of 1.36 gC m−2 a–1. The increasing growing season GPP was dominated by human activities, with a relative contribution rate of 59.84 %, ranging from 37.54 % to 89.21 %. The climate change was also an important factor affecting the growing season GPP with a median relative contribution of 40.16 %, ranging from 10.79 % to 62.46 %. This study provided a practical tool for estimating GPP at the growing season scale and offered opportunities to evaluate the effects of ecological projects and management on vegetation restoration. [ABSTRACT FROM AUTHOR]

• The hydrology changes is sensitive to energy in high-altitude. • The hydrology changes is controlled by water limitation in low-altitude area. • The water-energy coupling relation highly relies on altitudinal gradient. • Climate change dominate the hydrological shifts in alpine region. Hydrology heterogeneity refers to the different water regimes or hydrological processes in response to heterogeneous in topography, landscapes, land cover, soil properties, geology and meteorology reflecting as the spatial variation of precipitation, evapotranspiration and water yield along with landscape, elevation, terrain and climate variation. However, the hydrology heterogeneity in the alpine region of inland river basin has remained unclear to date, which limits the understanding of the hydrology and landscape interaction mechanism and affects the rational utilization of regional water resources. In this study, we combined the soil and water assessment tool (SWAT) and water-energy coupling framework to detect the hydrology heterogeneity in the arid alpine region of Heihe River Basin (HRB). We applied SWAT model to present the hydrological processes and regimes at different landscapes and elevation bands by using field measured parameters, and investigate the hydrology heterogeneity as well as the response to the changes in recent climate and land surface in the perspective of water-energy coupling framework. The results indicate that SWAT is indeed a robust tool in representing the streamflow process in alpine region with accurate performance. The distribution of landscapes reflect the comprehensive effect of regional water-energy coupling, which highly rely on the altitudinal gradient. The hydrology heterogeneity in high-altitude area is sensitive to energy and in low-altitude area is sensitive to water limitation (drought stress). Climate change is the dominate factor that driving the hydrology heterogeneity shifts in alpine region of HRB, while, the effect of land surface change is gradually strengthening over the past 50 years, reflecting with the contribution of land surface change on hydrology shifts is gradually increasing. [ABSTRACT FROM AUTHOR]

• WUE showed a significant increasing trend with a break point in 2002 in NWC. • A robust coupled attribution analysis with elasticity method was employed. • GPP contributed 88%, while ET a contributed 12%, to variation in WUE. • Precipitation was the primary factor driving the 66% increase in WUE. • A structure diagram was developed to present the driving mechanism of WUE variation. Besides contributing to a broader understanding of ecosystem-hydrology interactions, ecosystem water use efficiency (WUE) is a key factor operating in an ecosystem's balance between carbon assimilation and water transpiration. However, the effects of climate, elevated atmospheric CO 2 concentration and land surface changes on variation in regional WUE are sparsely documented. To elucidate the driving mechanisms of spatiotemporal variation in WUE in northwest China (NWC) between 1982 and 2015, the contribution of a changing environment — represented by the WUE's sensitivity to Gross Primary Productivity (GPP) and evapotranspiration (ET a) — was examined under different landscape types. Annual WUE series for NWC showed a significant increasing trend and a break point in 2002 with an increasing rate (7.40 mg C kg−1 H 2 O yr−1) prior to the break, and a slightly increasing rate (1.1 mg C kg−1 H 2 O yr−1) thereafter in NWC. A robust (Bias = 2.6%) attribution analysis revealed that GPP was the dominant factor contributing 88% variation in WUE, while ET a contributed 12%. Precipitation was the principal indirect driving factor that affected WUE variation in NWC, while the secondary factor was different among different landscapes. Regionally, precipitation drove 66% of the increase in WUE, wind speed contributed −15% of variation in WUE, and temperature contributed 12% of increase in WUE, while the remaining four factors contributed <3%. Compared to energy-related factors, water-related factors were the more sensitive drivers to WUE variation. The results can guide agricultural irrigation, integrated water resources management and ecological restoration under the changes in climate coming to Northwest China. [ABSTRACT FROM AUTHOR]

• A significant rise in ET a occurred over 75% of the vegetated area in NWC. • Results of ET a variation attribution by different methods were compared. • Partial correlation coefficient-based elasticity method was robust in capturing ET a variation. • Precipitation was the dominant variable driving the variation in ET a in NWC. Actual evapotranspiration ( ET a) has significantly increased under recent climate and vegetation changes. Discriminating the primary driver of ET a variation would improve our knowledge of the interaction between regional hydrological and ecological systems. In this study, a reliable ET a dataset was obtained by validating three ET a products from different sources with in-situ observations. We modified the elasticity-coefficient method using partial correlation, and compared it with the traditional regression-based method in estimating ET a variation in northwest China (NWC). On the basis of the magnitude and the sensitivity of ET a variation, results revealed that annual ET a significantly increased (2.32 mm/yr, p ≤ 0.05) in NWC over 1982–2015 with over 75% of the vegetated area showing an increasing trend. Robust in capturing spatial variation patterns in ET a , the partial correlation coefficient-based elasticity method was able to explain 83% of the annual variation in ET a. Precipitation, temperature, and NDVI were the most important factors controlling the increase in annual ET a from 1982 to 2015. Regionally, precipitation was the dominant factor and contributed 73% to the variation of annual ET a in the vegetated NWC. However, the contribution rates of precipitation varied across the different land cover types and ranged from 31% in irrigated cropland to 81% in the steppe. Potential uncertainty in the attribution of causative factors could arise in selecting the separation method and potential driving factors. Establishing a reliable relationship between ET a and potential driving factors should be confirmed with observations. The present study's results can guide sustainable water resources management and ecological restoration in water limited regions. [ABSTRACT FROM AUTHOR]