Long-term trends of dust events over Tibetan Plateau during 1961-2010

In this study we analyzed dust events records of surface meteorological stations on Tibetan Plateau (TP) during 1961-2010 and provided the spatial and temporal distribution of dust events. The occurrence of dust events has significantly decreased since the 1970s. We defined the Tibetan Plateau Dust Index (TPDI) for the most dust active periods, spring and winter, to characterize the large scale variability of dust events over TP. Mann-Kendall test suggested the decreasing trend was possibly an abrupt change in the 1990s. The decline of surface wind speeds could partly explain the decrease of dust events over TP. TPDI is positively correlated to the surface winds, with correlation coefficients of 0.42 for spring and 0.46 for winter, respectively. The averaged number days with strong winds (wind speed greater than 6.5 ms(-1)) for the 4 selected stations, which were chosen to define TPDI, are significantly correlated with TPDI for both spring (correlation coefficient = 0.69) and winter (correlation coefficient = 0.76) and also showed a deceasing trend. The upward trend of vegetation cover was indicated by the normalized difference vegetation index (NDVI), which can be attributed as another factor driving the decrease of dust events over TP. TPDI is negatively correlated to the NDVI, with correlation coefficients of -0.48 for spring and -0.29 for winter. Additionally, analysis of geopotential height fields and wind fields indicate an enhanced ridge in the north of TP and weakened westerly jet in the low-frequency years of dust events, which also drive the decline of dust events over TP. (C) 2015 The Authors. Published by Elsevier Ltd.