Simulation And Projection Of The Climate Over Southwest China And The Surrounding Regions

Using the high-resolution CRU (Climatic Research Unit) data, the observations at124stations in Yunnan Province, NCEP/NCAR reanalysis wind field and Hadley Centre SeaSurface Temperature (SST) data, this paper analysed the temporal and spatial characteristicsof precipitation over Southwest China surrounding regions, and possible mechanisms causingprecipitation variation were discussed as well. Sensitivity experiments were designed toanalyse the impact of early drought on late climate over Southwest China and discuss thepotential impact of land-atmosphere interaction on consecutive season drought events. Theperformance of7global ocean-atmosphere coupled models CMIP5data to simulate theclimatology over Southwest China e and the surrounding regions had been evaluated, and theprojected change of climate over the regions under different future emissions in2006-2055was also studied.Firstly, this paper analysed the spatial and temporal variation of precipitation overSouthwest China and the surrounding regions, discussing the possible mechanisms causingprecipitation variation in terms of circulation background, the monsoon activity and air-seainteraction. The whole year there could be separated dry and wet seasons apparently. Summerand autumn added up rainfall counting for more than75%of total annual precipitationshowed a significant linear decrease trend during the nearly50a. Precipitation in summer andautumn has obvious interdecadal oscillation characteristic with different cycle characteristics.It was pointed out that continuous drought occur in Southwest China recent years is likelycaused by the decadal-scale periodic negative phase superposition of precipitation in summerand autumn. There were significantly difference between atmospheric circulation duringdrought periods and that during flood periods in summer and autumn. It was found that theintensity of the monsoon activity in Indochina and SST in India-Pacific warm pool had closelinkage with summer and autumn precipitation.Secondly, a series soil moisture sensitivity experiments running by Regional climatemodel RegCM were designed to analyse the possible impact of early drought on consecutivedrought late over Southwest China. Reduction of soil moisture led convective precipitationdecrease, the ground temperature increase, sea level pressure decrease over the forced area, with an anomalous anticyclonic circulation response in the low-troposphere, and vice versa.The above responses to soil moisture had an obvious asymmetry. The impact of reducing soilmoisture on the climate latter was more pronounced. The early shortage of precipitation overSouthwest China made the continues drought prone, with the cumulative effects formation ofland-atmosphere feedback process.Finally, the performance of7global coupled ocean-atmosphere models (Coupled ModelIntercomparison Program5, CMIP5) from IPCC AR5(Intergovernmental Panel on ClimateChange5th Assessment Report) to simulate the climatology over Yunnan Province and thesurrounding regions had been evaluated, the projected change of climate over the regionsunder different scenarios of greenhouse gas emissions in2006-2055was also studied. Globalcoupled ocean-atmosphere models could simulate the spatial structure of temperature andprecipitation climatology, the temperature linear rising trend, and the decadal oscillationcharacteristics of spring precipitation, summer precipitation as well. The multi-modelensemble (MME) showed better skill than single model, and temperature simulation wasbetter than precipitation. Spring precipitation and summer precipitation was superior to otherseasons, making total annual precipitation simulation was better than autumn and winter.Future scenarios projections indicated that temperature over the study regions would appear asignificant linear rising trend, precipitation would keep decadal oscillation characteristics withan increase in the next50years. Some regions including Yunnan Province and its southernregions would undergo a relatively drought period before2020.