Decadal Variation Of Droughts In China And Its Prediction

From the angle of drought's key impact factors, objective method of detection and predictability of extreme drought events, and its decadal variations we study the spatio-temporal characteristics of drought's formation and variation in China. Based on homogeneous temperature, precipitation and the Palmer Drought Severity Index (PDSI) data between 1958 and 2007 of 194 stations in China, quantitatively measured the impact of global warming and precipitation variations on the formation of drought in China through a statistical model. Under the background of global warming, the trend of drought in north China still persists. The most probable region of drought in the next five years shows a tendendy of expansion, especially in the direction of south. Decreased precipitation is still the key factors in drought formation for most regions. However, in North, Northeast and eastern Northwest China, global warming plays a bigger role in drought's formation.During the period of late 1990s to early of the 21st century, the percentage of severe drought (PDSI<-3.0) is unprecedented under the background of global warming and the variation of the distributions of area coverage of droughts in different seasons is uneven. The distribution of spatial extent and durations of severe droughts follows a power-law, e.g. the spatio-temporal characteristics of severe droughts appear to be scale free. In general the area of severe droughts is closely correlated with its duration, while the deviations of the linear fit of correlation is also high.We investigate precursors and predictability of extreme events of Lorenz system with different percentile, the precursors and predictability of PDSI extremes in China are analyzed, and obtained how the quality of the predictions depends on the size of the extreme events and on the correlation strength. Results indicate that for extreme events of Lorenz system and PDSI series, the more extreme, the better predictable. Moreover, we analyzed precursors and predictability of eight regions in China and provide certain scientific basis for flood and drought predictions.Furthermore, we studied the key factors of climate system on the decadal scale and its influence on the variation of characteristics of drought over China. Results indicate that in the middle and lower reaches of Yangtze River and South China, the coirrelation coefficient between Pacific Decadal Oscillation (PDO) and PDSI exhibit periodic variation of half year scale. Meanwhile, the relationship of inverse correlation between PDO and northern China is not only limited to North China, but also include eastern Northwest, southern Northeast and Huang-huai.In order to predict the turning points in long-term trends of droughts over China it is proposed to construct nonlinear dynamics model only from turning points' magnitudes and intervals. Utilizing PDSI datasets of 569 stations in China in last 50 years, we obtained the possible long-term upward or downward trends and turning points in droughts of the next five years. Results indicate that the aridication of North and Northeast China will be continued while the droughts of eastern Northwest China would be eased.Aiming at overcoming the shortage of sample volume in the prediction of turning points, basic ideas of the spatio-temporal series analysis method are introduced, and the prediction roles of this method are given. Furthermore, we perform hindcast test on the modified predictive model of turning points. The preliminary results show that spatio-temporal series analysis can efficiently improve the ergodicity to enhance the predictive skill of turning points model effectively compared with the single point time series analysis.