*5.1. Recycled Moisture in Inland River Basins*

5.1.1. Differences between Mountainous Areas in Inland River Basins

The XYR Basin is located in the east of the Qilian Mountains and is a marginal area of the summer monsoon. Its moisture source is significantly different from that in most arid regions. The portion of moisture from the southeast and southwest in the monsoon period (June to September) is higher than in most inland river basins [6]. The sum of *fTr* and *fEv* recirculated moisture in the XYR Basin is about 10.34%, which is lower than that in Yeniugou, Hulugou, and Pailigou, which are located in the central Qilian Mountains [4], and higher than the Tianshan Mountains [21]. The main reason for the difference in the contribution of recirculated moisture in different regions is *fTr*. The *fTr* values calculated in various studies vary greatly, while the proportion of *fEv* is close to other stations. For XYR basin *fEv* is 4.81%, for bison ditch 3.6%, for Hulu ditch 5.9%, and for the dew ditch 0.9%. Controlled by meteorological factors, there are also obvious differences in recycled moisture at different elevations in the same watershed. In high elevation areas, *fTr* and *fEv* will be higher due to summer plant growth and frozen soil melting. At sampling point A (Foothill), *fTr* is relatively higher in spring and autumn, but soil moisture is lower due to less precipitation, resulting in a lower *fEv*.

In terms of spatial distribution, the vegetation cover is higher in site B and C than D. However, the recycling ratio in D is the highest in all four seasons. A possible reason accounting for this spatial pattern is that recycling ratio is scale-dependence [41]. We used site A as the unique upwind site for all sites B–D. As a result, the recycling ratio in D is the accumulated recycled moisture from site A to D and accumulated from site A to B for recycling ratio in site B. That is why recycling ratio increases with elevation rise, while vegetation and evapotranspiration are actually low in high-elevation regions due to the low air temperature. Scale-dependence is an important issue in recycling research but often is overlooked in isotope-based studies. This is also the reason why the isotope-based result is much smaller than model-based results.

#### 5.1.2. Recycled Moisture Contribution in Mountainous, Oasis, and Desert Areas

The average contribution of *fTr*, *fEv*, and *fAdv* to precipitation was 5.53%, 4.8%, 90.89% in the mountains area, 21.9%, 7%, and 72% in the oasis region and 10%, 5% and 85% in the desert and gobi region [6]. In Heihe River Basin, the average contributions of *fTr*, *fEv*, and *fAdv* vapor to precipitation were 24.15%, 26.9%, and 51.05% in the oasis region, 15.1%, 6.3%, and 21.4% in the desert region [4]. In the Urumqi River Basin, the average contribution of oasis *fTr* and *fEv* to precipitation was 15.09% [21]. Our study mainly studies the Xiying River Basin in the eastern part of the Qilian Mountains, this area is mountainous, the *fTr* (proportion of plant transpiration water vapor in precipitation) and *fEv* (proportion of surface evaporation water vapor in precipitation) is less than 10% throughout the year. It is in line with the local water cycle characteristics of the mountain areas in arid inland river basins. In general, the proportion of recycled water in the mountain areas of arid inland river basins are lower than those in the oasis and desert areas.

With the increase in population and utilization of the oasis area, the land use has changed. The cultivated land and ecological land must be maintained by artificial irrigation in the oasis area. Since canals and flooding can affect local evaporation, the growth of crops and forests can affect *fTr,* which will change the contribution of recycled moisture rates in oasis areas, and this is different from the characteristics of moisture recirculation in the mountainous area.

#### *5.2. Recycled Moisture in Precipitation in Different Regions*

The contribution of recycled moisture is lowest in the North and South poles, while the highest values are found in the Tibetan Plateau, the Patagonia Plateau, and the Andes Mountains. The vast ocean provides a large amount of moisture for the moisture cycle in various regions in the world. At the same time, the latent heat from condensation absorbed and released by the vapor phase transition also promotes the flow of global energy. There is a continuous high-value area in the mid-latitudes regions [42]. In tropical coastal areas, the contribution of recirculating moisture in different landscapes is only marginally different, with a contribution around 31~37% [19]. In the marginal zone of the temperate monsoon, the source of water is complex, and the climate is changeable. The contribution of circulating water in mountainous areas, oasis and deserts, and its temporal and spatial changes are quite large [6]. In addition, lakes have a significant impact on recycled moisture, contributing 5–16% in temperate continental monsoon climate zones [13], and 10–20% in temperate marine climate zones [43], 16–50% in tropical islands [17], and 3~37.9% are in the Qinghai-Tibet Plateau [16]. Our study area is the eastern part of the Qilian Mountains. This area is on the edge of the East Asian monsoon. The temporal and spatial changes of the local water cycle are complex. The proportion of local circulating water in precipitation is smaller than that in mid-latitude regions and tropical coastal regions. However, for small areas, the circulating water in mountain areas is greater than in oasis and desert areas.

The δ2H was used in the ice core to estimate that the contribution of recycled moisture in the Qinghai-Tibet Plateau has increased in the past few decades [44,45]. It is believed that the increase in the global temperature leads to strong local surface moisture evaporation and local moisture recycling [46]. Secondly, any increase in the vegetation coverage on the land surface and the evapotranspiration associated with this increase also has a particularly strengthening effect on local moisture recycling [6]. When we study the local water cycle, we should also consider the effects of long-term climate change and local human activities.
