Abstract: To master the characteristics of irrigation requirement during the whole growth period of double cropping rice in Yazhou district, Sanya city, Hainan province and provide a reference basis for irrigation water allocation in planting area, this study analyzed the changes of local reference crop evapotranspiration（ET₀）, crop water requirement（ET_c）, effective precipitation（P_e）, net irrigation water requirement（IR）, irrigation requirement index（IRI）based on the daily meteorological data of Sanya city and the statistics of crop growth in local early and late rice planting areas for the period of 2002—2022 by using the Penman-Monteith formula and the single-crop coefficient method and combining with the trend rate as well as Mann-Kendall trend test. The results showed that: the ET₀ in Sanya city ranged from 1 115.8 to 1 213.5 mm, and showed a not significant increasing trend with trend rate of 0.72 mm/a and the mean value of ET₀ 1 152.9 mm from 2002 to 2022. The ET_c, P_e, and IR during the whole growth period of early rice ranged from 399.5 to 448.3 mm, from 94.4 to 200.9 mm, and from 205.5 to 353.0 mm respectively. ET_c showed a not significant increasing trend with trend rate of 0.28 mm/a, and IR showed a not significant decreasing trend with trend rate of -0.18 mm/a. The ET_c, P_e, and IR during the whole growth period of late rice ranged from 357.1 mm to 402.9 mm, from 266.1 to 422.7 mm, and from -65.7 mm to 126.2 mm respectively. ET_c showed a significant increasing trend with trend rate of 0.78 mm/a, and IR showed a not significant increasing trend with trend rate of 2.04 mm/a. The crop water requirement of early rice at each fertility stage showed a trend of “jointing-booting stage”>“late tillering stage” >“tillering stage”>“milky ripening stage”>“heading and flowering stage”>“yellow maturity stage”>“transplanting and returning green stage”. The crop water requirement of late rice at each fertility stage showed a trend of “jointing-booting stage”>“tillering stage”>“milky ripening stage”>“late tillering stage”>“heading and flowering stage”>“yellow maturity stage”>“transplanting and returning green stage”. The irrigation requirement index of early and late rice in Yazhou district ranged from 0.51 to 0.79 and from -0.18 to 0.32 respectively, and a mean value of IRI were 0.67 and 0.09 respectively. It showed that early rice in Yazhou district relied on irrigation to a much greater extent than late rice, and that relying only on effective rainfall could not meet the needs of crop growth, and was prone to drought and water shortages, which required supplemental irrigation during the growth period.

Key words: double cropping rice, reference crop evapotranspiration, effective precipitation, crop water requirement, net irrigation water requirement, irrigation requirement index