Spatio-Temporal Characteristics of Drought and Its Effect on Wheat Yield in Southwestern China.

The global climate was changing featured with the temperature rising and large variability of precipitation, which resulted in more meteorological disasters and vulnerability of agricultural production. Southwestern China, featured with complex topography, was one of the major wheat production zones in China, but it was vulnerable to drought disaster, especially in recent years. To quantify the drought intensity during the wheat growing season and the impact of drought on yield, the APSIM-wheat model was selected to simulate the wheat growing process during 1961-2010 in Southwestern China. Based on the drought index relating to crop photosynthesis in APSIM model, a new drought index (SWDP) was developed to quantify the drought for three growing phases (sowing to floral initiation, S-FI; floral initiation to flowering, FI-F; flowering to maturity, F-M) and the whole growing season, and to indicate the effect of drought on yield loss. The relationship between drought intensity in different growing phase and the yield reduction rate was analyzed. The results indicated that drought mostly occurred in Yunnan province, south of Sichuan and west of Guizhou, with the high drought intensity areas centered in Yunnan, suffering from moderate to severe drought. The slight drought mainly distributed in west of Guizhou and middle of Sichuan, severe drought concentrated in south of Sichuan. Drought intensity was lightened from 1960s-1990s, but aggravated since the beginning of 2000s, with the drought affected area first shrieked and then enlarged, prevailing to the east part of Guizhou and Sichuan, while drought in central part of Yunnan became obviously heavier. The frequency of severe drought was above 40% mainly in Yunnan, while that was around 10% in west of Guizhou for the whole growing season. The yield reduction rate decreased from southwest to northeast, which was consistent with drought intensity distribution.