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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]

• 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]

• 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]