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Six global climate models (GCMs) from Coupled Model Intercomparison Project Phase 5 under three Respectively Concentration Pathways (RCP2.6, RCP4.5 and RCP8.5) were used to assess the impact of climate change on streamflow for the Huangnizhuang catchment (HNZ) in China. Change factor method was used for bias correction between GCM outputs and observations and the SWAT model was used to simulate the hydrological processes. The results indicated that the SWAT model performed well in the study catchment with a monthly Nash-Sutcliffe efficiency (NS) of 0.93 and 0.91 and daily NS of 0.63 and 0.68 for calibration and validation periods respectively. Their corresponding relative errors were -2.2 and 8.9, and -2.6 and 8.5 % respectively. The ensemble of multi-GCMs projected an increase of precipitation in the middle and end of twenty-first century over the HNZ, ranging from -2.4 to 9 %. However, streamflow is likely to decline in the future, ranging -6.9 to 0.8 %, mainly due to an increase of evapotranspiration in a warming world, as air temperature shows steadily increases for all the GCMs and RCPs. Average monthly streamflow from six GCMs are likely to increase in August and September but decline from October to June. The associated uncertainties of the reported results were also discussed. It includes, but is not limit to, different GCMs, emissions scenarios, downscaling techniques as well as hydrological simulations. The results of this study can inform planning of long-term basin water management strategies taking into account global change scenarios.

Ecohydrological processes in a water-limited environment are sensitive to both climate conditions and human activities, but the response mechanisms have rarely been explored for large endorheic river basins via an integrated modeling approach. This study established an integrated surface watergroundwater model for the Heihe River Basin (HRB), China's second largest endorheic river basin, using GSFLOW as the modeling platform. Evapotranspiration (ET) and Leaf Area Index (LAI) data independently derived from remote sensing products were compared and correlated, respectively, with the modeling results. Scale-dependent interrelationships among ecological, hydrological, and human-impact (i.e., diversion and pumping) variables were revealed through multiple regression analyses. Major study findings include: (1) the independent ET and LAI data enabled the modeler to crosscheck the modeling results from a unique angle not possible with conventional groundwater and streamflow observations; (2) controlling factors for the temporal variability of ET and LAI exhibit notable scale-dependence, reflecting distinctive climate, and human impacts on different land covers; and (3) there exists an intricate linkage between the hydrological regimes in the lower HRB and the middle HRB, essentially equivalent to a tradeoff between the ecosystem health of the lower HRB and the sustainable development of the middle HRB. Overall, the integrated modeling assisted by the independent ET and LAI data has provided a coherent understanding on the regional water cycle, and led to new insights on tackling the existing water conflicts in HRB.

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.