Influence of large-scale irrigation and irrigation water sources on pan evaporation

Using monthly 20 cm pan evaporation data, annual precipitation at six typical meteorological stations in Jining city of Shandong province, and the corresponding irrigated areas data in the same areas, the influence of large-scale irrigation on pan evaporation in mid-latitude region of China was investigated, for revealing the intrinsic relationship between the development of artificial irrigation and the decrease of pan evaporation. The results showed that there was highly significant correlation between pan evaporation data and irrigated areas data at different stages. The correlation in irrigation stage was higher than that in non-irrigation stage or over the whole year. At the same time, the decrease of pan evaporation in irrigated regions using groundwater irrigation was greater than that using surface water irrigation. These results suggest that large-scale, high-intensity irrigation has caused strong influence on the meteorological factors of the near-surface atmosphere, which plays an important role in the decrease of pan evaporation.