Abstract
The impact of global climate change on agroecosystems is growing, affecting reference crop evapotranspiration (ET0) and subsequent agricultural water management. In this study, the climate factors temporal trends, the spatiotemporal variation, and the climate driving factors of ET0 at different time scales were evaluated across the Northern Yellow River Irrigation Area (NYR), Central Arid Zone (CAZ), and Southern Mountain Area (SMA) of Ningxia based on 20 climatic stations’ daily data from 1957 to 2018. The results showed that the Tmean (daily mean air temperature), Tmax (daily maximum air temperature), and Tmin (daily minimum air temperature) all had increased significantly over the past 62 years, whilst RH (relative humidity), U2 (wind speed at 2 m height), and SD (sunshine duration) had significantly decreasing trends across all climatic zones. At monthly scale, the ET0 was mainly concentrated from April to September. And at annual and seasonal scales, the overall increasing trends were more pronounced in NX, NYR, and SMA, while CAZ was the opposite. For the spatial distribution, ET0 presented a trend of rising first and then falling at all time scales. The abrupt change point for climatic factors and ET0 series was obtained at approximately 1990 across all climatic zones, and the ET0 had a long period of 25a and a short period of 10a at annual scale, while it was 15a and 5a at seasonal scale. RH and Tmax were the most sensitive climatic factors at the annual and seasonal scales, while the largest contribution rates were Tmax and SD. This study not only is important for the understanding of ET0 changes but also provides the preliminary and elementary reference for agriculture water management in Ningxia.
Highlights
Evapotranspiration (ET) is an important component of the hydrological cycle and essential for understanding land surface processes in climatology [1]
Study Area and Climate Data. e Ningxia Hui Autonomous Region (NX) (35°14′∼39°23′N, 104°17′∼107°39′E) is part of the Yellow River basin and is located among the Alxa Plateau, the North China Plateau, and the Qilian Mountains folds. e area consists of Northern Yellow River irrigation area (NYR), Central Arid Zone (CAZ), and Southern Mountain Area (SMA) and has a total area of 6.6 × 104 km2 [28] (Figure 2). is region faces a serious shortage of water resources and a huge contradiction between water supply and demand
Across the three different regions (NYR, CAZ, and SMA), Tmean, Tmax, and Tmin had significantly increased with similar variation. e increasing rates of Tmean (0.38°C/10a), Tmax (0.36°C/ 10a), and Tmin (0.54°C/10a) were the largest in the Northern Yellow River Irrigation Area (NYR), while the CAZ was the smallest (0.31°C/10a, 0.24°C/10a, and 0.48°C/ 10a, respectively)
Summary
Evapotranspiration (ET) is an important component of the hydrological cycle and essential for understanding land surface processes in climatology [1]. The productivity is closely related to actual ET in agricultural research; ET has important implications for improving local agricultural water management [2]. E reference evapotranspiration (ET0), which is defined as the potential ET of grass, can be used to prepare input data for hydrology models (e.g., SWAT model), schedule irrigation systems, and calculate the actual evapotranspiration (ET) in a basin or a region [3]. In order to revise the reference evapotranspiration (ET0) calculation criteria, the Penman–Monteith method has been recommended by Food and Agriculture Organization (FAO) Irrigation and Drainage Paper No 56 [4]. Due to the easy calculation and ease of data access, the FAO56 has become one of the Advances in Meteorology bestselling and most cited publications in the field of water resources management up to now [5]
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