Modulating meteorological effects and optimization strategies of irrigation during compound drought-heatwave event in various oasis ecosystems of Northwest China

The arid regions of Northwest China (NWC) frequently experience compound drought-heatwave (CDHW) events during summer, where irrigated oases play a key role in mitigating extremes and sustaining agricultural productivity. However, the response of various oases to irrigation, irrigated water allocation strategy under CDHW remain insufficiently understood. Using convection-permitting and irrigation-diversified regional climate simulations, we evaluate climatic effects of different irrigated oases in NWC during CDHW. Results show that oasis irrigation significantly mitigates drought and heatwave, leading to reduction in 2 m air temperature ( T ) by 0.21 °C and an increase in 2 m relative humidity (RH) by 0.75%, accompanied by enhanced latent heat flux (LH) by 3.41 W m −2 , reduced sensible heat flux (HFX) by 1.42 W m −2 . Ranking of oasis effects about cooling and humidification efficiency due to irrigation is alluvial plain oases (APO) > mountain fan oases (MFO) > river valley oases (RVO) > intermontane corridor oases (ICO). Irrigation induces diurnally asymmetric circulation pattern characterized by a daytime "cold suction" mechanism and a nocturnal "cold discharge" process. In addition, a nonlinear response is identified, with optimal range of 40 (± 1.6) – 68.8 (± 1.6) mm and theoretically maximum oasis area 5000–8000 km 2 , within which the oasis effects are most efficient to resist a 10-day CDHW event. These results further support irrigation supply that prioritizes APO and MFO, then guarantees the basic agricultural production of RVO and ICO if facing constrained water resources. This study provides guidance for optimizing irrigation and water allocation to maintain oasis effects and agricultural development in arid regions under extreme climate conditions.