The spatiotemporal variation of reference evapotranspiration and the contribution of its climatic factors in the Loess Plateau, China

Abstract

Reference evapotranspiration (ET 0 ) is an important parameter of agricultural activity and hydrometeorological studies. In this study, we used the Food and Agriculture Organization Penman-Monteith equation to evaluate ET 0 , and to investigate the change point of ET 0 in the Loess Plateau region from 1960 to 2013. The results showed that a change point was detected at approximately the year 1990 for annual ET 0 series from 108 meteorological stations using Cramer's statistical test. The annual ET 0 decreased significantly (p \ 0.05) by -1.22 mm year -1 from 1960 to 1990, especially during the summer months, which contributed the most to the total annual reduction, while it increased significantly (p \ 0.001) by 1.15 mm year -1 from 1991 to 2013, with the spring months contributing the most. The ET 0 and its trend in the five integrated management divisions of the Loess Plateau have significant spatial heterogeneity. The highest and lowest ET 0 were found in the third and fifth divisions from 1960 to 2013. The ET 0 decreased significantly in the first division and increased in the fourth divisions (1960-1990 and 1991-2013, respectively). Using differential equations to quantitatively evaluate the contribution of various factors, the wind speed was mostly responsible for the variability in the ET 0 trend from 1960 to 1990, followed by solar radiation and vapor pressure. The positive effect of air temperature on ET 0 trend was offset by the other three factors, and the combined effects of the four climatic variables led to the decrease in the ET 0 trend. However, the rapidly increasing air temperature became the predominant factor in the change in the ET 0 trend after 1990. A spatiotemporal variation of predominant contribution to the ET 0 trend was identified. The temperature dominant region changed from the third to the first division for 1960-1990 and 1991-2013. Radiation did not change. Vapor pressure changed from the first to the fourth and the wind speed changed from the forth to the third. This study could contribute to a better understanding of the response of the spatial and temporal variation of ET 0 to increased climate change. Additionally, this research also provides scientific support to regional planning and management.

Reduced Runoff Due to Anthropogenic Intervention in the Loess Plateau, China

“…Critical Z values of ±1.64, ±2.58, and ±3.29 were used for the probabilities of p = 0.1, 0.01, and 0.001, respectively. Spatial interpolation with the Kriging method and zonal statistical method in the ArcGIS 10.2 spatial analysis toolbox [34] was used to obtain the spatial distribution of the monthly and annual precipitation and the LAI and NDVI information in each basin.…”

“…The rainy season, from June to September, accounts for approximately 65% of the total precipitation, most of which is in the form of frequent high-intensity storms [34]. Vegetation cover consists of forest, forest steppe, typical steppe, and desert steppe zones from southeast to northwest, and the land use is predominantly cultivated croplands and improved grassland.…”

“…This implies that a larger absolute ε ET0 has caused the considerable decrease in runoff since 2000. However, researchers have documented that the ET 0 increased significantly in China [56] and the Loess Plateau [34] since the 1990s. Additionally, Zhang et al [57] predicted ET 0 with three GCMs in China and found ET 0 will increase by 2.13%-10.77%, 4.42%-16.21%, and 8.67%-21.27% during the 2020s, 2050s, and 2080s compared with the average annual ET 0 during 1960-1990, respectively.…”

Changes in reference evapotranspiration over China during 1960–2012: Attributions and relationships with atmospheric circulation

“…To attribute ET 0 changes over China and its subregions, various methods have been proposed and used (e.g., the differential equation method (Zhang et al, ), multiple linear regression technique (Zhang et al, ), and sensitivity analysis [Gao, He, Dong, & Bian, ]). Nevertheless, due to complex interactions among various meteorological factors for ET 0 (Paparrizos, Maris, & Matzarakis, ; Zhang et al, ; Zhang et al, ), it remains difficult to identify the impact of each driving factor alone, which consequently results in uncertainties and even errors in the conclusions (Li et al, ; Liu et al, ; Zhang et al, ). Recently, to overcome this issue (at least partially) and enhance the confidence level of the conclusions, Sun, Chen, Ju, et al () developed a new separation method to attribute ET 0 changes over Southwest China and stated that this method has a better performance (e.g., accuracy) compared with other methods.…”

Variation of Aridity Index and the Role of Climate Variables in the Southwest China

“…The Mann-Kendall statistical test is a commonly used approach in detecting the trend in hydro-meteorological variables due to its robustness for non-normally distributed data [25,27,29,[40][41][42][43]. It presumes a steady time series (x 1 , x 2 .…”