Abstract:

The Weihe River Basin is located in the semiarid and semihumid transition region of northern China and experiences frequent drought events; therefore,study of droughts in the Weihe River Basin is of great importance.Based on the precipitation and temperature data from 28 meteorological stations,the spatial and temporal variation characteristics of dryness were analyzed by using the Mann-Kendall（M-K）trend test,empirical orthogonal functions,and wavelet transform analysis.At the same time,the relationship between drought characteristics and six largescale climatic factors was studied,and the potential impact of the main factors on the spatial and temporal characteristics of drought was further discussed.According to the research,we obtained results showing that the Weihe River Basin exhibits a drought trend between 1961 and 2017.Particularly,after 1990,the drought degree and number of drought phenomena in the basin increased greatly and the average Standardized Precipitation Evapotranspiration Index (SPEI) decreased from 0.34 during 1961-1990 to -0.37 during 1991-2017.Empirical orthogonal function analysis shows that there are three typical modes in the wet and dry distribution field of the Weihe River Basin.The global type with corresponding modal eigenvalues of 50.43% is characterized by either drought or humidity and is the main control mode of dry distributions in the Weihe River Basin; northwest-southeast reverse distribution type with corresponding modal eigenvalues of 17.35% shows that the northwest and southeast regions have different drought characteristics; eastwest reverse distribution type with corresponding modal eigenvalues of 5.06% shows that the eastern and western regions have different drought characteristics.Finally,the research reveals that the Southern Oscillation Index (SOI),which represents ENSO events,exhibits the strongest correlation with drought distribution in the Weihe River Basin and from the perspective of phase analysis,abnormal SOI variations will generally bring more drought events to the Weihe River Basin.

Key words: Weihe River Basin, drought, standardized precipitation evapotranspiration index, empirical orthogonal function, wavelet transform analysis