Changes in aridity index and reference evapotranspiration over the central and eastern Tibetan Plateau in China during 1960–2012

Based on climate data from 68 meteorological stations over the Tibetan Plateau (TP) observed by the China Meteorological Administration in 1960–2012, temporal and spatial variations in aridity index (AI) and reference evapotranspiration (ET0) were comprehensively investigated. The abrupt change and the period in AI and ET0 were characterized using a comprehensive time series analysis conducted with Mann–Kendall test and Morlet wavelet. The results indicated that the regionally averaged value of AI significantly decreased by 0.04/decade during 1960–2012 period, with the maximum observed in 1972. Similarly, the regional trend for ET0 was at the rate of −9.6 mm/decade with statistically significant at the 0.01 level. Most of these stations with positive value for AI were primarily distributed at the northern southwestern TP. Moreover, a majority of stations with low values of ET0 were substantially distributed at the central and eastern TP, and amounts of the stations with high values of ET0 were mainly located at a lower elevation. Abrupt changes of both AI and ET0 primarily happened in 1980s. The major cycles of AI and ET0 were 15 y and 17 y scale over the study period with apparent periodic oscillation characteristics, respectively, and together with other different scale cycles co-existing. The significant correlations between AI and East Asian Summer Monsoon Index (EASMI) indicated that AI over the TP was related to the EASMI.