Abstract:

Shanxi Province,China is located between 110.23°-114.55°E and 34.56°-40.73°N and has a total area of approximately 15.67×10⁴ km²;it is located on the eastern Loess Plateau of China,with altitude mostly more than 1 000 m above sea level.Shanxi Province has a temperate continental monsoon climate with distinct seasons and is a semiarid and semihumid zone according to the dryhumid climate zones.Located in the northern margin of the East Asian monsoon,it is greatly affected by the interannual variation of the intensity of the East Asian monsoon,which causes frequent drought disasters and creates a fragile ecological environment.The surface dry/wet conditions exert important effects on local agriculture,forestry,and animal husbandry production.For these reasons,by using statistical methods,the temporal and spatial characteristics of the aridity index (AI),interdecadal changes of dry/wet areas were analyzed,and relationships between surface dryness and meteorological factors were investigated on the basis of AIs calculated by the modified PenmanMonteith model of the Food and Agriculture Organization of the United Nations;this study used meteorological observation data from 67 stations in Shanxi Province from 1961 to 2017.Quality controlled data obtained from the Shanxi Meteorological Information Center were used,including annual precipitation,daily maximum and minimum temperatures,average wind speed,sunshine hours,and relative humidity from 1961 to 2017;the data for the longitudes,latitudes,and altitudes of stations were also used.The statistical methods used mainly include trend analysis,Pearson correlation analysis,and partial correlation analysis.The results can be summarized as follows:(1) Based on an annual AI of 2.0,Shanxi Province can be divided into semiarid and semihumid zones,which are in good agreement with the observed vegetation coverage.(2) The northern and southeastern parts of Shanxi Province show a wetting trend,while most of the southwest shows a drying trend.(3) The AIs show an overall increasing trend from the 1960s to the 1990s,followed by a decreasing trend;precipitation levels exhibit an opposite trend,and the changes in evapotranspiration are divided into three stages,namely an upward trend from the 1960s to the 1970s,almost no trend from the 1980s to 2000,and then an upward trend after 2000.(4) The boundaries of semiarid and semihumid lands move to the southeast from the 1960s to the 1990s and move northwest after the 1990s;the corresponding proportions of the total area of semiarid areas expand from 52% to 73% and then decrease to 23%.(5) Both precipitation and evapotranspiration exhibit prominent effects on aridity,and the correlation of precipitation with dryness is greater than with evapotranspiration. Relative humidity,average wind speed,and sunshine hours affect dryness via evapotranspiration.The correlations between maximum/minimum temperatures and dryness/evapotranspiration are not significant.(6) The interdecadal trend of desertification in northwest Shanxi is consistent with dryness.These changes imply that the dry/wet condition is an important factor affecting desertification.The major difference from previous studies is the shift from drying to wetting.Our conclusions can be used to guide agricultural and animal husbandry production,forestry production planning,desertification control,and ecological environmental construction,especially in northwest Shanxi.A key problem to be solved is the accurate estimation of solar radiation in areas with no radiation observations and a modification of the PenmanMonteith formula for different types of reference crops or land use types to render the calculated evapotranspiration values suitable for different surfaces.In the future,it will be helpful to guide agricultural production,ecological environmental construction,and desertification control to establish an index similar to dryness and to define a threshold that can accurately depict the spatial distribution of the vegetation extent or desertification.

Key words: FAO PenmanMonteith, aridity, climate, Shanxi