Spatio-temporal Variation Characteristics of Extreme Climate Events and Their Teleconnections to Large-scale Ocean-atmospheric Circulation Patterns in Huaihe River Basin,China During 1959–2019

Huaihe River Basin(HRB) is located in China's north-south climatic transition zone, which is very sensitive to global climate change. Based on the daily maximum temperature, minimum temperature, and precipitation data of 40 meteorological stations and nine monthly large-scale ocean-atmospheric circulation indices data during 1959–2019, we present an assessment of the spatial and temporal variations of extreme temperature and precipitation events in the HRB using nine extreme climate indices, and analyze the teleconnection relationship between extreme climate indices and large-scale ocean-atmospheric circulation indices. The results show that warm extreme indices show a significant(P < 0.05) increasing trend, while cold extreme indices(except for cold spell duration) and diurnal temperature range(DTR) show a significant decreasing trend. Furthermore, all extreme temperature indices show significant mutations during 1959-2019. Spatially, a stronger warming trend occurs in eastern HRB than western HRB, while maximum 5-d precipitation(Rx5day) and rainstorm days(R25) show an increasing trend in the southern, central, and northwestern regions of HRB. Arctic oscillation(AO), Atlantic multidecadal oscillation(AMO), and East Atlantic/Western Russia(EA/WR) have a stronger correlation with extreme climate indices compared to other circulation indices. AO and AMO(EA/WR) exhibit a significant(P < 0.05) negative(positive)correlation with frost days and diurnal temperature range. Extreme warm events are strongly correlated with the variability of AMO and EA/WR in most parts of HRB, while extreme cold events are closely related to the variability of AO and AMO in eastern HRB. In contrast, AMO, AO, and EA/WR show limited impacts on extreme precipitation events in most parts of HRB.