宁夏沿黄绿洲参考作物蒸散演变特征及其归因

参考作物蒸散(Reference crop evapotranspiration,ET₀)是生态水文过程中的关键因子,研究ET₀在干旱绿洲区的演变,不仅有助于理解气候变化背景下的绿洲水文过程响应,亦对绿洲水土资源高效配置和生态系统稳定性维持有指导意义。以宁夏沿黄绿洲为例,基于1960-2019年的气象资料和Penman-Monteith模型计算ET₀,利用Mann-kendall突变检验、相对敏感系数和Morlet小波分析等方法,对宁夏沿黄绿洲近60 a的ET₀演变特征及其归因进行研究。结果表明:(1)宁夏沿黄绿洲ET₀年内呈单峰形态,ET₀在5-7月间较高,累积ET₀占年总ET₀的43.6%;近60 a的ET₀年均值为1226.38 mm,并以1.66 mm/a(P ＜ 0.01)幅度上升,但年际波动特征明显,其中在1988年突变之前,ET₀无显著变化趋势,而突变之后则以每10 a左右的周期显著增加或降低。(2)年ET₀主要以20-40 a和50-60 a周期振荡,且有多重时间尺度的复杂嵌套现象,不同季节的周期振荡差异较大,夏、秋季振荡幅度较强,其周期接近于年ET₀规律,而冬、春季振荡幅度较弱。(3)虽然ET₀与6种气象因子均存在显著相关性,但ET₀对不同气象因子的敏感性存在差异,其中对最高温度和相对湿度的敏感性较高,敏感系数分别为11.58%和8.40%。(4)宁夏沿黄绿洲ET₀与区域气候变化特征有较强的耦合性,区域气候的持续升温和相对湿度持续降低、以及由此引发的饱和水汽压亏缺持续增强是推动ET₀上升的重要原因,而气候由湿润向干旱的突变和平均风速的异常波动是诱发ET₀突变的原因。

Change characteristics of reference crop evapotranspiration of the Yellow River Oasis in Ningxia autonomous region and its driving analysis

Reference crop evapotranspiration (ET₀) is a key factor in eco-hydrological processes. The study of ET₀ evolution in arid oasis areas not only helps us to understand the response of hydrological processes of oasis in the context of climate change but also has a guiding significance for the efficient allocation of soil and water resources in oasis and the maintenance of ecosystem stability. In this paper, we took the Yellow River Oasis in Ningxia autonomous region as an example, calculated ET₀ based on meteorological data from 1960 to 2019 and the Penman-Monteith model, and used the Mann-Kendall test, relative sensitivity coefficients, and Morlet wavelet analysis to study the characteristics of ET₀ evolution and its driving mechanism in the oasis over the past 60 years. The results showed that: (1) ET₀ of the Yellow River Oasis in Ningxia presented a single peak pattern within a year. The ET₀ was higher from May to July and its accumulated value accounted for 43.6% of the total annual ET₀. The annual ET₀ from 1960 to 2019 was 1226.38 mm and increased with an amplitude of 1.66 mm/a (P ＜ 0.01). However, the fluctuation characteristics of interannual ET₀ were significant in that the ET₀ had no trend before the mutation year of 1988 while it increased or decreased significantly with a cycle of about every decade after that. (2) The annual ET₀ mainly oscillated with cycles of 20-40 and 50-60 years, while its cycles overlapped complicatedly in multiple time scales. Furthermore, the cycle and magnitude of oscillation in different seasons varied greatly. The oscillation cycles in summer and autumn were close to that of the annual, but the oscillation magnitude was stronger than that in winter and spring. (3) Although there were significant correlations between ET₀ and the six meteorological factors used to calculate ET₀, the sensitivity of ET₀ to different meteorological factors varied. The sensitivity of ET₀ on maximum temperature and relative humidity was higher, and the coefficients were 11.58% and 8.40%. (4) There was a strong coupling between ET₀ and the regional climatic changes of the Yellow River Oasis in Ningxia.air temperature sustained warming, relative humidity sustained decreasing, and their aerodynamic coupling result in vapor pressure deficit increasing were critical to promote the enhancement of ET₀. Meanwhile, the mutation of regional climate from wet to dry and the abnormal fluctuation of average wind speed were the reasons to induce the abrupt change of ET₀.