Document Type : Research Paper
Authors
1 Assistant Professor, Soil Conservation and Watershed Management Research Department, Khorasan Razavi Agricultural and Natural ResourcesResearch and Education Center, AREEO, Mashhad, Iran
2 Associate Professor, Soil Conservation and Watershed Management Research Department, Khorasan Razavi Agricultural and Natural ResourcesResearch and Education Center, AREEO, Mashhad, Iran
Abstract
Introduction
Drought propagation, defined as the transfer of moisture deficits from meteorological to hydrological drought, represents a central topic in water resources management, particularly in arid and semi-arid regions. Understanding the spatial patterns of drought propagation and identifying the controlling factors are essential for designing risk-reduction strategies and achieving sustainable management of aquifers and surface runoff. Considering the sensitivity of catchments to climatic stress in eastern Iran, this study aims to analyze the spatial dynamics of drought propagation and assess the influence of catchment environmental characteristics in Khorasan Razavi Province.
Materials and methods
This study utilized data from 46 catchments over a 29-year period (April 1988 to September 2016). Meteorological and hydrological droughts were identified using the standardized precipitation index (SPI) and the standardized streamflow index (SSI), respectively. Drought events were extracted using a threshold of SPI or SSI ≤ –1, and paired events were determined. For each event, the intensity and severity of both meteorological and hydrological droughts were calculated, followed by the derivation of drought propagation ratios and their normalized forms. A set of physiographic and climatic catchment variables-including slope, normalized difference vegetation index (NDVI), precipitation seasonality index (Ps), snow fraction (fₛ), aridity index (Ai), and available water capacity (AWC)—were averaged at the catchment scale and analyzed using Pearson correlation to assess their relationships with drought propagation ratios.
Results and discussion
Spatial analyses indicated that the mean meteorological drought intensity ranged from 0.23 to 2.17, with an average of approximately 2.1, whereas hydrological drought intensity ranged from 0.14 to 1.16, with a mean of 0.65. The coefficient of variation (CV) was 63% for hydrological drought intensity and 37.7% for meteorological drought, indicating greater spatial variability in hydrological drought. At the catchment level, 54% of the catchments exhibited a reduction in propagation intensity, and 67% showed a decrease in propagation severity. The mean propagation intensity and severity ratios were –0.03 and –0.1, respectively, suggesting a general attenuation of drought effects during the transfer from meteorological to hydrological systems. Significant negative correlations between meteorological drought characteristics and propagation ratios (r = –0.48 for intensity and r = –0.67 for severity) indicate that stronger meteorological drought events tend to experience greater attenuation during propagation; that is, high-intensity meteorological drought does not always translate into equally severe hydrological drought. Among environmental factors, NDVI showed a significant negative relationship with both propagation ratios, and AWC was negatively correlated with the severity propagation ratio. In contrast, precipitation seasonality (Ps) and aridity index (Ai) did not exhibit significant correlations with propagation ratios, while snow fraction (fₛ) showed only a weak negative correlation with propagation intensity. Catchment slope also showed no significant relationship with propagation ratios. These patterns suggest that, in Khorasan Razavi, intrinsic catchment characteristics—particularly vegetation cover and soil water storage capacity—play a key role in attenuating drought propagation.
Conclusions
The results of this study indicate that drought propagation in the 46 catchments of Khorasan Razavi is predominantly characterized by a reduction in both intensity and severity, with 54% of catchments showing decreased propagation intensity and 67% exhibiting reduced severity. The mean propagation ratios for intensity and severity were –0.03 and –0.1, respectively. Meteorological drought intensity and severity emerged as the strongest controls on drought propagation, showing significant negative correlations with propagation ratios. Among environmental factors, vegetation cover (NDVI) and soil water storage capacity were the most influential in mitigating drought propagation, whereas climatic indices had no significant impact.
Keywords
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