Publications

Abdi, O; Shirvani, Z; Buchroithner, MF (2018). Spatiotemporal drought evaluation of Hyrcanian deciduous forests and semi-steppe rangelands using moderate resolution imaging spectroradiometer time series in Northeast Iran. LAND DEGRADATION & DEVELOPMENT, 29(8), 2525-2541.

Abstract
Advanced MODIS data have provided diverse products for assessing and monitoring natural vegetation affected by droughts. Between 2000 and 2016, we estimated monthly precipitation anomalies in the deciduous forests and semi-steppe rangelands of northeastern Iran using kriging models, and analyzed 16-day vegetation anomalies using vegetation greenness and water content indicesincluding the enhanced vegetation index, the normalized difference vegetation index (NDVI), and the normalized difference water index (NDWI). Vegetation anomalies showed high positive responses to interseasonal precipitation anomalies over the 17-year period, and low positive responses to monthly precipitation deficits during critical droughts. Forest and rangeland anomalies recorded higher Moran's coefficients based on the NDVI (I=0.253 +/- 0.102) and NDWI (I=0.284 +/- 0.087) with interseasonal precipitation anomalies, respectively. Throughout critical droughts, the NDWI anomalies showed higher coefficients with monthly precipitation deficits for both forests (I=0.0716 +/- 0.059) and rangelands (I=0.125 +/- 0.0615). Nevertheless, there were only significant differences between the Moran's coefficients of the three vegetation indices for rangelands (F=2.873; p<0.05). BiLISA maps indicated that sparse forests show higher spatial associations with drought conditions (High-high cluster), whereas dense forests experienced lower stresses by severe droughts (High-low outlier) during drought periods. Meanwhile, some severe vegetation stresses occurred at locations with low droughts (Low-high outlier), which indicate the impact of other significant climate-induced disturbances on vegetation anomalies.

DOI:
10.1002/ldr.3025

ISSN:
1085-3278