关键词: 潜在蒸散量, Penman-Monteith公式, 陕西省, 气候变化

Abstract:

The temporal and spatial variations of characteristics of potential evaporation in Shaanxi Province is analyzed by the methods of Mann-Kendall, the trend of Sen, and the wavelet analysis, at the same time, the strength of the impact on climate factors is analyzed by the methods of multiple regression analysis, through the Penman Monteith - the formula to calculate the reference crop evapotranspiration recommended by the United Nations food and agriculture organization(FAO), on the basis of 16 weather stations observation log data in 1981-2010. The results show that, potential evaporation presents a increasing trend in 1981-2010, with the growth rate reaching about 3.1 mm/a, and it does not pass significant level inspection of 0.05. Presenting a volatility trend of"Weak reduction-strong increase-decreases", which appears a turning point in the early 1990s and in the late 1990s.There exists an oscillation cycle showing about 2 a, 5 a, 8 a,22 a,32 a in the study area, the biggest shock energy is 32 a, and the second is 22 a. In the research period, it appears an obvious mutation in 1992, with the match of the biggest shock energy in 32 a of the cycle fluctuation. The interspace of the potential evaporation in Shaanxi province shows an obvious difference owing to the span latitude and complex topography. The average amount of the potential evaporation is between 166.9-1 367.5 mm for many years, among them, the value of the potential evapotranspiration in Qin Bashan area is the highest,the second is in shanbei region, and the lowest area is in the guanzhong plain. The tendency of the variation shows a descending trend from north to south, the areas where the obvious increase trend of the potential evaporation is in southern shaanxi region, so the guanzhong area and the northern shaanxi region showed a trend of decrease. The HURST index distribution presents a decreasing trend from east to west,which accounted for 77.11% of the entire study area with the index between 0.4-0.5. It shows that there is a weak inverse continuous changing of the potential evapotranspiration in the future and in the past. There is an obvious seasonal difference in the potential evaporation,among them, the change in summer and spring is most obvious,followed by autumn and winter. The dominated rate of contribution is in summer, followed by the spring,and autumn and winter is the least. The average temperature, relative humidity and wind speed have a larger influence on the potential evaporation, the average temperature play the biggest role and the effect is positive, followed by the relative humidity, but the effects on the potential evaporation is negative. Average sunshine time and air pressure play a weak positive role on the potential evaporation.

Key words: potential evaporation, Penman Monteith formula, Shaanxi Province, climate change