Change of drought and its impact on potential yield of wheat in agricultural region of Shan-Gan-Ning region in 1961－2010

Abstract: As a typical meteorological disaster, drought has made serious impacts on human being. Especially during the recent decades, the frequency of drought has increased along with climate change. Researches on the change in the drought occurrence and its impacts will become more important to reduce the negative impacts of climate change. In this study, the agricultural region of Shan-Gan-Ning region, which was located in the eastern part of the Northwestern China and belonged to arid and semi-arid region, was chosen as the study area due to its vulnerability to climate change. Spring wheat and winter wheat were 2 main crops in this region and selected as the research crops. The trends in agricultural drought and its impact of crop yield were analyzed by drought index and crop growth simulation. Palmer drought severity index (PDSI), was used to analyze the change of agricultural drought in different periods and regions. It was based on the water balance in soil and considered the previous soil moisture, which had been widely used to analyze the temporal and spatial distribution of agricultural drought. The trends of precipitation, temperature and PDSI in different months from 1961 to 2010 were investigated. Then the impact of drought on crop growth of wheat was analyzed by the crop growth simulation. Crop growth model, which was built based on the crop growth mechanism, could simulate the change of soil water deficit and crop growth in a long period. It had become an important method to the research on the impact of climate change on the crop yield. The crop growth under rainfed and efficient irrigation scenarios was simulated by the environmental policy integrated climate (EPIC) model. The crop yield under the efficient irrigation scenario could eliminate the negative impact of water deficit and reflect the impact of local condition on crop growth such as solar radiation and temperature. The rainfed condition showed the synthesized effect of local condition. The crop yield gap between those 2 scenarios was recognized as the impact of water deficit by lower precipitation. Over the past 50 years, it showed a significant increasing trend in temperature in this region, especially in January and February. There were significant decreasing trend in the precipitation in April, July and September. Increasing temperature and decreasing precipitation would result in more serious water deficit condition. PDSI had a significant decreasing trend in the eastern part of Northwest China in 1961－2010. The number of months with severe drought (PDSI was less than -3.0) showed a significant increasing trend. Both of them indicated that drought had become more severe and more frequent. Especially in April, July and September, PDSI was much less than before because of the decreasing trend of precipitation in these months. Since many important crop growth stages were in those months, drought during this period would have more serious impact on the crop yield. Those stations that were distributed in the central part of this region had a larger negative trend in PDSI, because of the more reduction in precipitation. Based on the crop growth simulation, almost all the stations had an increasing trend on crop yield reduction caused by water deficit over the past 50 years. The situations in the central part of study area, especially for the northwestern stations in winter wheat growth region, had larger change range in the yield reduction. All of those stations had more serious water deficit condition because of the decreasing trend in precipitation, especially in April, which was jointing and heading stage and key to crop growth. The PDSI in those stations also had decreasing trend. The central parts of the study region should be more concerned by the agriculture and water resource managers, especially in April, July and September.