Validating the Modified Perpendicular Drought Index in the North China Region Using In Situ Soil Moisture Measurement

Soil moisture content is one of the most important variables for monitoring and assessing the drought condition. In this letter, a modified perpendicular drought index (MPDI) derived from the Moderate Resolution Imaging Spectroradiometer satellite data was validated using in situ soil moisture measurements in Henan province of North China. The soil moisture at different depths of a soil layer and time lag on usefulness of the MPDI for estimating soil moisture content was analyzed; the effectiveness of the MPDI was evaluated with the observed soil moisture content and the comprehensive drought index K for different soil types. The results showed that the MPDI was significantly correlated with soil moisture content for the top soil layer with 10 cm depth. For a time lag ranging from 0 to 4 days, the correlation of MPDI to soil moisture was significant with no time lag in the depth of top 10 cm (r = -0.867). For the stations of the same soil texture type of loam, the correlation coefficient between MPDI and soil moisture is higher than that of all soil texture types. In a regional scale, the MPDI reflected an obvious spatial pattern of drought under different growing stages in the drought years over the study area.