The few studies that examined actual evapotranspiration reported that actual

evapotranspiration would increase over the TP generally but with spatial variations (Yang et al., 2011, Zhang et al., 2007a and Zhang et al., 2007b), and the result would be less available water for streamflow. Cuo et Dabrafenib al. (2013a) looked at the impacts of actual evapotranspiration change on streamflow and found that increases in actual evapotranspiration were larger during May–October when compared to the other months. The same authors noted that actual evapotranspiration change was the second most important factor besides precipitation change in causing the annual and seasonal streamflow decreases in YLR. The difficulty in obtaining existing MS-275 chemical structure hydrological observations collected and maintained by the Chinese Ministry of Water Resources and the local bureaus of water resources due to their data policies and the harsh environment unfavorable for setting up and maintaining hydrological observational sites on the

TP pose great challenges for hydrological research in the region. Overcoming these challenges requires sustained and coordinated efforts from all levels of agencies and researchers alike. In addition, there are other hydrological research topics on the TP that need to be addressed. Among them, three most important scientific issues are discussed below. Climate systems dictate precipitation and temperature on the TP, which in turn regulate streamflow. Large-scale atmospheric systems such as the mid-latitude westerlies, East Asia and Indian monsoons, North Atlantic Oscillation, mafosfamide Arctic Oscillation, ENSO and local circulations all play roles in affecting the weather and climate of the TP (Tian et al., 2007, Cuo et al., 2013b, Yao et al., 2013 and Gao

et al., 2014). As an example, Wang et al. (2006) showed that above-average annual precipitation in YLR and YTR is caused by enhanced moisture transport by the Indian monsoon when Mongolian low pressure and the westerlies are weak. Li et al. (2007) reported that above normal precipitable water vapor is transported to TRB by the intensifying westerlies as the northerlies become weakened. Any changes in precipitation would have strong implications for streamflow in the basins. Relating streamflow to climate system indices could potentially reveal the impacts of the climate systems on streamflow and help understand the spatial and temporal changes of streamflow over the TP. Ding et al. (2007) compared the annual streamflow changes among YLR, YTR and BPR and found that the changes were out of phase between YLR and BPR, and they attributed that to the differences in the prevailing systems.