Northwest China (NWC) experiences arid and semi-arid climates and is highly vulnerable to climate change. 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 (U 2 ), and sunshine duration (SSD) were further quantitatively analyzed. This study reveals a shift in pan evaporation drivers in NWC around 1990, from U 2 -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 U 2 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. • Continuous daily D20 and E601 pan evaporation datasets (1961–2020) across northwest China were developed. • Persistent warming and declining relative humidity drove increasing pan evaporation after 1990 in Northwest China. • After 1990, pan evaporation increased in Xinjiang and Gansu, while Qinghai and Northern Shaanxi declined. • D20 was more temperature-sensitive while E601 responded more to wind speed and sunshine duration.
Jiang et al. (Fri,) studied this question.