Impacts of various types of El Nino-Southern Oscillation (ENSO) and ENSO Modoki on the rainy season over the Huaihe River basin

Precipitation is a significant parameter in many aspects such as agriculture, water management and climate variability. To characterize rainy season variations is important to understand precipitation variability under the effect of climate change. In this study, rainy season features (i.e., onset, retreat and rainy-season precipitation) over the Huaihe River basin (HRB) and the response to different types of El Nino-Southern Oscillation (ENSO), that is, central Pacific warming (CPW), eastern Pacific warming (EPW), eastern Pacific cooling (EPC), conventional ENSO and ENSO Modoki in the developing and decaying phases are evaluated. The multi-scale moving t test was used to capture onset and retreat of rainy season. The possible dynamic causes of ENSO-induced precipitation over the HRB, such as monsoon and atmospheric circulation, were also explored. Results show that (a) onset (retreat) of rainy season progressed northwards (westwards), with rainy-season precipitation increasing from north to south; (b) rainy-season precipitation showed a strong correlation to Sea Surface Temperature (SST) in Nino regions. Dry and wet signals were identified in different regions of the HRB in the developing and decaying phases of CPW, EPC and EPW. Special attention should be paid on decaying EPW, where totally dry signals were found, which can reach down to 25% below average precipitation; (c) developing El Nino Modoki and decaying El Nino showed totally dry signals, with decaying El Nino Modoki and conventional La Nina demonstrating overall increasing precipitation; (d) different performances of ENSO-induced precipitation during rainy season over the HRB are attributable to the combined influences of the monsoon from the India Ocean and the anticyclonic flow in the western North Pacific (WNP). Stronger anticyclone and monsoon are generally associated with increasing rainy-season precipitation. These results can improve predictability of rainy season features and ENSO-induced precipitation over the Huaihe River basin.