Spatial and Temporal Variation of Evapotranspiration of Soil Water across Guangdong Province during Past 40 Years

Potential evapotranspiration values of 12 weather stations in 1971 ~ 2010 in Guangdong province were calculated and compared by Peman-Monteith formula. The characters of spatial and temporal variation were analyzed.The results showed that the potential evapotranspiration values declined with the increasing latitudes and ranged680-1800 mm a-1, which being mainly controlled by temperature and precipitation. The potential evapotranspiration values increased with climate warming. The minimum was in 1980 s, and the maximum was in 2000 s, and the mutation point appeared in 2004. The highest potential evapotranspiration values separately existed in the summer Middle subtropical zone and spring South subtropical zone and North tropic zone, while the lowest ones always occurred in winter. Surface wetness index was highest in May and June and lowest in November; it values seasonally decreased as spring summer autumn winter. The moist index declined significantly with the decrease of latitude, especially in spring and winter. The wetness degree was highest in the 1980 s, and lowest in the 2000 s, and decreased greatest in spring. Soil moisture content wasn't maintained in a suitable condition during crop growth. And soil water deficit led to droughts at different levels in different seasons, including the autumn drought in all areas, spring drought in the south areas and winter drought in the middle and south areas. The spring drought was more serious in the south than in the north of Guangdong province, while the autumn drought was more serious in the north than in the south of Guangdong province. One of the most effective ways for sustainable development of local agricultural industry is to take effective and specific measure for the individual drought area.