Abstract: Based on the climate data of daily temperature, precipitation, wind speed, sunshine hours as well as relative humidity at nine meteorological stations in Ningxia during 1961-2012, evapotranspiration (ET₀) was estimated by the PenmanMonteith model. Additionally, inverse distance weighting was applied to investigate the temporalspatial variations of ET₀, precipitation and aridity index. The abrupt change and the period in ET₀, precipitation and aridity index were characterized using a time series analysis conducted with moving ttest and Morlet wavelet. The results showed that in recent 52 years, the ET₀ and precipitation presented a decreasing trend on the whole with rates of -8.64 mm·10 a^-1 and -10.04 mm·10 a^-1, respectively; aridity index displayed a slightly increasing trend (0.01 10 a^-1), suggesting a drier climate trend in Ningxia. Moreover, both the ET₀ and precipitation exhibited a unimodal type of distribution with peaks appearing in August (66.82 mm) and July (118.12 mm), respectively, and aridity index showed a valleylike type with minimum (0.42) in August. For spatial distribution of the aridity index, it presented an increasing trend from south to north, suggesting that climate got drier from south to north. Abrupt changes of ET₀, precipitation and aridity index primarily happened in the late 1970s, early and midterm 1980s, and the large time scales of these abrupt changes were same (21 a) and in agreement with the period (22 a) of sunspot activity. Besides, their fluctuations in the short periods of 3, 5 and 7 years were correlated to atmospheric circumfluence and El Nino
events to some extent.

Key words: biochar, adsorption., silk waste, Cd²⁺, pyrolysis temperature