Agricultural drought evolution characteristics and driving mechanisms in the Yellow River Basin under climate and land use changes

Agricultural drought has posed a serious threat to the national food security, social, environmental, and economic sustainable development in China over the last 20 years. The average annual disaster area has been accounted for more than 50% of natural disasters against climate warming and intensive human activities. Therefore, it is highly urgent to clarify the drought evolution and driving mechanisms for scientific drought prevention. More importantly, the Yellow River Basin provides the water supply for about 140 million people in the region, where about 15% of the total irrigated land was for agricultural irrigation in the country. However, the Yellow River Basin has historically been frequently experiencing serious droughts. For example, the disaster area caused by agricultural drought after 2000 was nearly six times that before 2000. Therefore, taking the Yellow River Basin as a study area, the main objective of this study is to comprehensively analyze the temporal and spatial evolution characteristics and driving mechanisms of agricultural drought. Six sub-basins were divided according to the climatic and topographic characteristics. The standard soil moisture index (SSMI) and threshold method were used to identify the duration, intensity, and drought events under different drought levels. A systematic analysis was also made on the agricultural drought characteristics and event frequencies in different zones in the study area on the annual and seasonal scales. A SWAT model in a simulation scheme was then selected to quantify the impacts of climate and land use land cover (LULC) change on agricultural drought in the study area. Results showed that: 1) The fewer frequencies occurred for the agricultural drought with longer duration, as the cumulative time was much longer. The duration of the agricultural drought was then remarked by SSMI-1, SSMI-6, and SSMI-18 corresponding to about 1-8, 1-12, and 1-22 months, respectively. The beginning and end time of agricultural drought was mainly concentrated in spring and summer. 2) The most serious agricultural drought occurred in the study area during 1981-1990, where that was greatly alleviated in most zones during 2001-2010. Specifically, Zone C and A were the most vulnerable to severe and extreme agricultural drought in the 1990s and 2000s, respectively. 3) Climate change was the main factor that caused the agricultural drought in the study area with a contribution rate of about 50%-90%, while the impact of LULC change was relatively weak with a contribution rate of about 10%-50%. Consequently, the greatest driving impacts of climate and land use were about 60%-90% and 10%-50%, respectively, on the frequency of agricultural drought in the study area. The findings can provide much more accurate information for actual management and disaster prevention of agricultural drought.