Located in the interior of Eurasia, the Mongolian Plateau (MP) is extremely sensitive to global warming and become a critical area for studying precipitation patterns. Based on the monthly data of 135 meteorological stations during 1976–2017, we analyze the spatiotemporal change in precipitation and discuss its response to atmospheric circulation. The results show that: (1) Precipitation shows increasing trends in spring, autumn, and winter, but a decreasing trend at a rate of 5.3 mm/decade in summer. The annual precipitation also shows an overall slight decreasing trend. (2) The spatial distribution is uneven, the annual precipitation in the northern Great Khingan Mountains is more, but it gradually decreases at the rate of 10–30 mm/decade, showing a trend of “wet gets dry”; while there is less in the southwest Gobi Desert region, but it gradually increases with the rate of 10–20 mm/decade, showing a trend of “dry gets wet”. (3) Over decades, the East Asian summer monsoon (EASM) and westerly circulation show a seesaw change in MP. Affected by the weakening of the EASM, the area of arid regions has gradually expanded. The results also demonstrate that the EASM has a higher impact on the annual precipitation change pattern, particularly in the southeastern MP. The conclusion indicated that the variation in the position and orientation between EASM and the westerly circulation may be an explanation for the spatiotemporal precipitation pattern, providing a new viewpoint to the question of circulation mechanisms behind climate change in MP in recent 40 years.

The Huolin River is located in the monsoon marginal zone in Northeast China. It is an important source of the wetland system on the Northeast Plain. Recently, a dramatic reduction in the observed river runoff has resulted in a record high level of dried-up days in the Huolin River catchment (HRC). In this study, we used the hydrological simulation approach of the Soil and Water Assessment Tool (SWAT) model to evaluate the influences of climate change and human activities on runoff in the HRC. The SWAT model effectively simulated the streamflow changes in the HRC with a high accuracy. The R2 values were 0.71 and 0.69 for the calibration and validation periods, respectively. In addition, the Nash-Sutcliffe efficiency (NSE) index reached 0.69 and 0.66 for the calibration and validation periods, respectively. The simulation results demonstrated that the variations in runoff have mostly been caused by combined influence of climate change and land use/land cover (LULC) changes, but the contributions of these factors varied in each period. The climate factors contributed 84.5% of runoff fluctuations before 2000, while the effect of LULC changes gradually grew to 63.6% after 2000. The increase in the influence of LULC changes was mainly apparent in the considerable growth of the areas of the arable land and construction land, which increased by 607 and 113 km2, respectively. This study provides an effective scientific basis for establishing long-term water management in catchment scale and regional social and economic development under the changing environment.