Identifying Early Abnormal Signals of Sea-Level Pressure for Continuous Drought Events in Yunnan during Summer and Autumn

Over the past decade, Yunnan Provinces have experienced multiple instances of seasonal continuous drought. In particular, the prolonged drought in summer and autumn has exacerbated the negative effects of the drought in winter and spring, detrimentally impacting the local economic and social activities. As a result, the underlying reasons for the continuous droughts have become a major topic of concern. This paper utilizes precipitation data from 120 Yunnan Meteorological Bureau stations and sea-level pressure data of NCEP spanning the period from 1970 to 2020. This paper aims to analyze the evolution characteristics of continuous drought events in summer and autumn in Yunnan Province using the precipitation persistence anomaly index. Additionally, it investigates the possible relationship between drought events during summer to autumn and sea-level pressure in early April. The findings of this paper indicate that: (1) The primary characteristics of precipitation persistence anomaly in summer and autumn correspond to the consistent positive or negative anomaly in Yunnan. (2) The early stage of the continuous drought events in summer and autumn in Yunnan is the result of a combination of sea-level pressure anomalies in three regions, namely, the North Atlantic Ocean, the North Indian Ocean, and the Central Pacific Ocean. (3) Based on the previous three signals, an index, referred to as the SAP (Summer and Autumn Precipitation) index, can be constructed in the month of April. The SAP index can effectively represent the continuous precipitation anomaly in summer and autumn in Yunnan. This index demonstrates remarkable potential as an early prediction signal for continuous drought events in the region. The results predicted by this study can provide valuable insights for improving the prediction of such extreme events in Yunnan.