JIA-2018-09

2115 WANG Qian-feng et al. Journal of Integrative Agriculture 2018, 17(9): 2107–2117 water-consuming crops for farmland can help reduce soil salinization in the region. An increasing trend in ET in the areas covered by forest and grass is likely to increase higher water consumption by growing roots and above-ground biomass. 4.4. Correlations between environmental factors and ET A spatial correlation analysis measures the influences and responses between two spatial elements. In this study, to determine how environmental factors influence the ET in Hebei Province, we investigated the correlations of ET with two environmental factors including vegetation coverage and precipitation for 2000–2014. The correlation coefficient and significant level between vegetation coverage and ET are illustrated in Fig. 7-A, the correlation coefficient is positive in the whole study area, which showed that vegetation coverage is higher and the ET is higher, because the plant canopies with vegetation coverage can lead to plant transpiration. However, only very few areas which sparsely distributed in the farmland show the significant negative correlation ( P <0.05), this may be caused by the coarse spatial resolution with mixed pixels and irrigation. The correlation coefficient and significant level between precipitation and ET are illustrated in Fig. 7-B, the correlation coefficient is positive in the whole study area, which showed that precipitation is higher, the ET is higher, and precipitation is a key factor to impact ET. The absolute values of the correlation coefficient are great than 0.51 ( P <0.05) for most of the north areas, it indicates that precipitation influences the ET in broadleaved deciduous forest. 5. Conclusion Vegetation ET is an important component of hydrologic and climatic changes in the biosphere and insights into ET are vital to address issues of water resource shortage. We selected a typical salinized region as the study area in Hebei to explore the spatial-temporal evolution of vegetation ET, the following conclusions can be drawn: (1) Inter- and intra- annual variations of ET for each type of vegetation are consistent with the variation characteristics in the whole study area, the cultivated areas have a greater degree of spatial heterogeneity. (2) The area covered by broadleaved deciduous forests indicates higher ET levels and generally higher ET rates; and the area covered by grass shows lower ET levels and generally lower ET rates; vegetation coverage and precipitation are key factors influencing the ET with positive effects in the whole study area. (3) A widespread decline of ET was found only in cultivated areas, which can help relieve soil salinization in the region and ET displays an uptrend trend in other areas of vegetation. This study can provide a scientific understanding for the management of water resources management on a regional scale. However, it may be more productive to 140°E 42°N 41°N 40°N 39°N 38°N 37°N 42°N 41°N 40°N 39°N 38°N 37°N 42°N 41°N 40°N 39°N 38°N 37°N 42°N 41°N 40°N 39°N 38°N 37°N 115°E 116°E 117°E 118°E 119°E 140°E 115°E 116°E 117°E 118°E 119°E 140°E P <0.01 P <0.05 –0.64 0.64 –0.51 0.51 0 –0.64 0.64 R A B R –0.51 0.51 0 P >0.05 P >0.05 P <0.05 P <0.01 P -value P -value P <0.01 P <0.05 P >0.05 P >0.05 P <0.05 P <0.01 115°E 116°E 117°E 118°E 119°E 140°E 115°E 116°E 117°E 118°E 119°E Fig. 7 Spatial correlation coefficient ( R ) during 2000–2014. A, R between vegetation coverage and evaportranspiration. B, R between precipitation and evaportranspiration.