Abstract:Daily temperature and precipitation data from 136 stations of Southwest China (SWC) during the last five decades, from 1960 to 2007, were analysed to determine the spatial and temporal trends by using the Mann-Kendall trend test. Results show that SWC has become warmer over the last five decades, especially in the recent 20-25 years. The increasing trends in winter months are more significant than those in the months of other seasons, and spatially Tibet, Hengduan mountains area and west Sichuan Plateau have larger temperature trend in magnitude than the other regions have. A downward trend was detected in Sichuan Basin also, but the region with cooler temperature was shrinking due to the statistically significant increasing trend of temperature after 1990s. Both annual and seasonal means of daily maximum and minimum temperatures show an increasing trend, but trend magnitude of minimum temperature was larger than that of maximum temperature, resulting in the decrease of diurnal temperature range for SWC in the last 50 years. Annual precipitation showed slightly and statistically insignificant increasing trend, but statistically significant increasing trend has been detected in winter season while autumn witnessed a statistically significant decreasing trend. The results could be a reference for the planning and management of water resources under climate change.

Background: Extreme climate events leading to tremendous life and property losses, environmental degradation, have recently received increased attention. It is applied to a data set consisting of 116 weather station records ) covering the Southwest China, and measured the spatial and temporal characteristics of precipitation and temperature extreme and their long-term trend have been analyzed, the possible reason for the recent 2009 SWC severe drought is briefly discussed too. Results: The most remarkable result is, compared with the base year, significant decreasing trend has been measured for the precipitation amount and the rainy days while regardless the mean temperature, maximum temperature or minimum temperature is clear warming in 2009 over SWC, particularly in the 9-12 month, less precipitation combined with unreasonable high temperature may be the major contributor to the mega-drought crippling into SWC in 2009-2010. Although no significant trend has been indentified for annual precipitation, great sub-seasonality and regional difference has been detected over SWC. Statistical significant decreasing trend has been examined for rainy days over SWC and the downward prevail in the second half of a year, especially in the autumn month while the first half of a year is characterized by positive trend of maximum precipitation, rainy day intensity and annual precipitation. Maximum temperature and minimum temperature showed significant warming trend in every month, in particular the upward trend of the minimum temperature is stronger than that of the maximum temperature.

Background: The impacts of climate change on streamflow in the Wujiang River watershed of Guizhou Province, Southwest China, were investigated by using a monthly distributed hydrological model and the two-parameter climate elasticity of streamflow approach. Results: Results showed two different approaches obtained almost identical results in term of precipitation elasticity of streamflow, which is about 1.42 across different emission scenarios. Precipitation is the primary factor controlling runoff generation. However, the effects of temperature on the streamflow cannot be neglected with evidences of opposite signs of future precipitation and streamflow; the slight decline of streamflow is associated with an increase of precipitation and a higher temperature. Conclusion: While the magnitudes of annual mean streamflow responses are minor, there would be a seasonal shift: drier spring and wetter summer would potentially result in the increasing frequency of spring drought events and summer flooding, and would produce serious challenge for water resources planning and management for Southwest China.

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