Drought Changes in Southwest China and Its Impacts on Rice Yield of Guizhou Province

Extreme weather and climate events have become more frequent and severe in recent years in the context of global warming. These extreme events bring serious impacts on human survival and sustaining development of society. Drought is one of the major types of extreme climatic events in China, which seriously affects agriculture and social-economic development. The domestic extreme drought events in recent years mostly occur in Southwest China, influencing the agriculture severely. Using the high quality observations from 348 weather stations and the agriculture data of county level in Southwest China, the complicated relationship among droughts, water supply, and rice yields is investigated.The precipitation decreases in Southwest China from 1951 to 2012, with an average decadal decrease of 16.9 mm per 10 years. In particular, the precipitation decreases distinctly from August to October, mainly due to the weak South Asian monsoon. Drought days are counted by using the drought index I_SWAP, and the result shows that the number of drought days generally increases by 3.3 days per 10 years in the past several decades, especially since 2001 due to the less precipitation. Since rice cultivation is irrigated agriculture, drought won't directly affect rice growth. To further understand the complexity, impacts of various drought events on rice yields are investigated using high quality rice yield data collected in 70 counties of Guizhou Province, and the result indicates that the drought has little adverse but favorable impacts on rice yields when annual accumulated number of drought days is less than 40 days. It is because that this kind of drought won't affect the rice irrigation water supply, and the temperature is usually abnormally high with more bright sunshine days during the period of drought which are actually favorable for rice growth. However, when the number of drought days is more than 86 days, rice yields will reduce by 20%-73% due to the drought and the insufficient irrigation. When the number of drought days is between 49-86 days, rice yields usually reduce by less than 20% but with large differences between different regions. This kind of drought has little impact on rice yields in regions of robust drought tolerance but greatly affects rice yields in regions of weak drought tolerance.