Abstract: Crop water requirement is an important basis for irrigation scheduling and water resources planning. Based on the daily meteorological data from 38 stations in Southwest of China during 1951-2012, the rice water requirement was estimated by using FAO Penman-Monteith equation, and the change of reference crop evapotranspiration trend was analyzed for rice. Meanwhile, the variation of rice water requirement in the growth period and the spatial distribution characteristics of reference crop evapotranspiration and irrigation requirement index for rice in Southwest of China were analyzed. The results showed that in recent 62 years, the reference crop evapotranspiration in the southwest area changed insignificantly over time and decreased with-increasing the latitude, which in the growth period accounted for 47.6% of the yearly average value. The water requirements in different growth stages showed a moderate variability, and the tillering and heading stages were the critical period. In Southwest of China, the averages of rice water- requirement and irrigation water requirement were 304.5 mm and 76.9 mm per year, respectively. The rice irrigation requirement index was averaged as 0.24, and increased from the west to the east but was generally less than 0.5. As a result, the degree of dependence of rice on irrigation water requirement was low in the study area.

Key words: urban forest, cooling effect, community structure