Monthly and annual temperature extremes and their changes on the Tibetan Plateau and its surroundings during 1963-2015

In this study, the spatiotemporal distributions of monthly and annual temperature minima (T-min) and maxima (T-max), extreme T-min and T-max, the highest (lowest) T-min (T-max), frost day (FD), icing day (ID), summer day (SD) and tropical night (TR) at 112 stations and over the ten large river basins on the Tibetan Plateau and its surroundings (TPS) during 1963-2015 are examined. Mann-Kendall test is applied for the trends. The analyses show: the northwest experiences the hottest summer while the central TPS has the coldest winter and most frequent frost and icing days. The northwest (southeast) features the highest (lowest) monthly extreme temperature ranges. The northwest has the most frequent hot summer days, whereas the southeast has the least frequent frost and icing days. The entire TPS displays few tropical nights. Most stations show positive trends for all monthly and annual T-min and T-max variables. February displays the most positive trends for both monthly T-min and T-max variables while April shows the highest number of stations with decreasing trends in monthly T-max. The trends of FD and ID are negative, whereas the trends of SU and TR are positive. Over river basins, the trends of monthly T-min are all positive and statistically significant and the trends of monthly T-max are all positive except for one negative trend and around 1/3 of the positive trends are statistically significant. Relatively larger increases in monthly T-min and T-max are noted for the cold season than the warm. The monthly and annual T-min variables increase more than T-max variables.