Study region: Northwest China (NWC) experiences arid and semi-arid climates and is highly vulnerable to climate change. Study focus: Global warming has intensified evaporation and exacerbated water scarcity in the (semi-)arid regions of NWC, where sparse meteorological stations and significant data deficiencies pose additional challenges. This study developed a continuous daily pan evaporation dataset of both D20 and E601 from 374 meteorological stations across NWC (1961-2020), and systematically analyzed the spatiotemporal patterns and driving factors of D20 and E601 pan evaporation across annual, freezing and non-freezing periods. The sensitivity of different pan types to key climatic variables including temperature, relative humidity, wind speed (U2), and sunshine duration (SSD) were further quantitatively analyzed. New hydrological insights for the region: This study reveals a shift in pan evaporation drivers in NWC around 1990, from U2-dominated decline to temperature/humidity-driven increase, elucidating the "evaporation paradox". Xinjiang and Gansu show increasing evaporation after 1990, while Qinghai and Northern Shaanxi show declines. D20 is more temperature-sensitive, whereas E601 responds more to U2 and SSD, explaining their divergence. These changes have direct implications for water resources management: increasing evaporation in Xinjiang and Gansu indicates higher atmospheric evaporative demand and irrigation water requirements, while declining or redistributed evaporation in Qinghai and Northern Shaanxi highlights the need for improved soil moisture conservation and optimized irrigation and water allocation.