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Long‐term trends in sunshine duration over Yunnan‐Guizhou Plateau in Southwest China for 1961–2005

Yunnan‐Guizhou Plateau (YGP), a low latitude highland region, covers the two provinces of Yunnan and Guizhou in Southwest China, where a cooling trend in the annual mean surface air temperature since the mid‐20th century was reported as a notable phenomenon of regional climate against the global warming. In this study on the regional climate, we applied the data of sunshine duration and cloud amount from 184 stations across the YGP from year 1961 to 2005. It was found that, over this 45 year period, annual sunshine duration decreased mostly north of 24°N on the YGP with the negative trends reaching −11.8% per decade, while during the same period it increased with the positive trends reaching +3.5% per decade at the stations concentrated on the southwestern YGP. An overall decline in annual sunshine duration over the northern YGP dramatically accelerated from the 1970s to 80s with its maximum rate in the 1980s, but has remarkably decelerated since the 1990s so that going into the 21st century the annual sunshine duration has ceased or even reversed its downward tendency. The evolution of annual mean cloud amount on the YGP was shown to be insignificant and even in decline over the 45 years, exerting less of an influence on the decreasing trends in the annual sunshine duration. The consistent patterns of sunshine duration trends and surface temperature changes on the YGP support the hypothesis that aerosol loading in the atmosphere could be involved in the surface cooling trend.