Study capability of Standardized Precipitation Evapotranspiration Index to represent soil moisture variability during winter season over Pakistan for the period 1951–2010

Abstract

Standardized Precipitation Evapotranspiration Index (SPEI) is a drought index, its potential is explored to be used as alternative to soil moisture using singular value decomposition (SVD) analysis. To conduct this study, soil moisture was simulated using Community Land Model version 3.5 with National Centre for Environmental Protection (NCEP) 6-h atmospheric-forcing dataset. Due to non-availability of long time continues observed data, simulated soil moisture (0–10 cm depth), is compared with Global Land Data Assimilation System (GLDAS) dataset. Standardized anomalies of area-averaged soil moisture of simulated and GLDAS soil moisture were compared for four different regions of the country. Simulated soil moisture is in strong agreement with GLDAS data. Mann–Kendall test was applied to find trend in soil moisture in the four selected regions. Except Region-1 all the other three regions show declining and significant (p ≤ 0.05) trend. SVD analysis reveals that the correlation between the expansion coefficients is 0.54 and 0.64 for the first and second dominant mode, respectively. First three modes capture more than 90% of the squared covariance fraction. The homogeneous and heterogeneous patterns of first two modes show that soil moisture (decreases) and drought (increases) in the south, while towards the north it is vice versa. Simulated soil moisture follow the same trend as SPEI. SPEI can explain variance of soil moisture.